How to get a gene of interest?

GENE CLONING:

"The cloning in which identical copies of genes are produced is called gene cloning".

PCR (Polymerase Chain Reaction):

"The reaction which is used for production of lesser number of gene copies within test tube".

While, in case of formation of large gene copies recombinant DNA technology is used.

RECOMBINANT DNA TECHNOLOGY:

Recombinant DNA means a DNA with two different combination of genetic materials. (It is also called Chimeric DNA).

Method for Production of Recombinant DNA:

(i) Interest: Gene of interest (OR) selection, which is used to be cloned.

(ii) Cut out: Scissors enzymes (restriction endonuclease) to cut out the gene of interest.

(iii) Placement: Molecular carrier or VECTOR, on which gene of interest could be placed

(iv) Introduction: The gene of interest along with the vector is then introduced into an expression system, as a result of which a specific product is made.

Three ways to get the gene of interest:

(i) Isolation of gene from the chromosomes.

(ii) Synthesis of gene chemically.

(iii) Making of gene from mRNA.

Procedure:

(i) Isolation by restriction enzyme: The gene of interest can be isolated from the chromosomes by cutting restriction endonuclease is used to cut on the flanking sites of the gene.

(ii) Synthesis of small genes: In case of small genes they can also be synthesized in the laboratory.

(iii) Use of reverse transcriptase: Genes may be synthesized from mRNA by using the reverse transcriptase (an enzyme). This kind of DNA is called complementary DNA i.e, cDNA 

Differentiate between Restriction endonuclease and ligase?

DEFINITIONS

Cloning: 
A technique for developing large numbers of genetically identical cells or organisms is known as cloning.

Recombination:
Formation of a new association of DNA molecules or part of DNA molecules is termed as recombination.

Vector:
A plasmid that carries an inserted pieces of DNA into a host cell in recombinant DNA technology

(OR)

Any DNA molecule, such as plasmid, which serves to carry foreign DNA into host cells, where it may be replicated and expressed.

Gene:
An unit of inheritance is called gene.

Genome:
The total genetic constitution of an organism is known as genome.


Q No.2 Differentiate between restriction endonuclease and ligase?

Restriction Endonuclease (Scissor):
(i) It is the enzyme which can cut a DNA molecule within the strand.
(ii) It is also termed as "scissor".
(iii) "Restriction endonuclease" recognizes specific nucleotide sequence in DNA and then cut both strands in specific manner.

Ligase (Glue):
(i) The enzyme which has ability to seal up the DNA molecule.
(ii) Is is also termed as "glue".
(iii) "Enzyme that creates bonds between the ends of DNA molecules and form a large polynucleotide".

Biotechnology and Gene Therapy

BIOTECHNOLOGY:

"The molecular genetics which enables us to manipulate genetic materials for the welfare of mankind".

Desired varieties are formed by gene recombinations. These recombinant genes are made for the production of substance such as enzymes, antibiotics, and hormones needed for human use.

GENE THERAPY:

"The process by which faulty genes are replaced by normal genes is known as gene therapy".

Genotype and then Phenotype of organisms may be changed for important and good results by gene therapy. "Genetic engineering means manipulation of genes by man"


★ Gene Therapy in Bacteria

Many kinds of useful bacteria have been reproduced by genetic engineering:

(i) Clean up Pollutants: Some genetically engineered bacteria are used to clean up environmental pollutants.

(ii) Increase the Fertility of Soil: Certain bacteria have been engineered which increase the fertility of soil.

(iii) Kill Insects Pests: Bacteria are also used to kill insect pests.

★ Gene Therapy in Man

(i) Medical Applications: These include the production of hormones, vaccines, enzymes, antibodies, antibiotics and vitamins, and the gene therapy for some hereditary diseases.

(ii) Human insulin has been prepared by this method. It plays an important role in treating the diabetic patients.

Genetic engineering is also playing excellent role in industrial applications, environmental applications, agricultural applications and biological researches.

Continuous Variation, Molecular Basis Of Allelic Variation

CONTINUOUS VARIATION A character showing continuous variation has an unbroken range of phenotypes in a population (see Figure 1-10b). Measurable characters such as height, weight, and skin or hair color are good examples of such variation. Intermediate phenotypes are

generally more common than extreme phenotypes. In some cases, all the variation is environmental and has no genetic basis, as in the case of the different languages spoken by different human groups. In other cases, such as that of the various shades of human eye color, the differences are caused by allelic variation in one or many genes. For most continuously variable characters, both genetic and environmental variation contribute to differences in phenotype. In continuous variation, there is no one-to-one correspondence of genotype and phenotype. For this reason, little is known about the types of genes underlying continuous variation, and only recently have techniques become available for identifying and characterizing them.

Continuous variation is encountered more commonly than discontinuous variation in everyday life. We can all identify examples of continuous variation, such as variation in size or shape, in plant or animal populations that we have observed—many examples exist in human populations. One area of genetics in which continuous variation is important is in plant and animal breeding. Many of the characters that are under selection in breeding programs, such as seed weight or milk production, arise from many gene differences interacting with environmental variation, and the phenotypes show continuous variation in populations. We shall return to the specialized techniques for analyzing continuous variation in Chapter 20, but for the greater part of the book, we shall be dealing with the genes underlying discontinuous variation.

Molecular basis of allelic variation

Consider the difference between the pigmented and the albino phenotypes in humans. The dark pigment

melanin has a complex structure that is the end product of a biochemical synthetic pathway. Each step in the pathway is a conversion of one molecule into another, with the progressive formation of melanin in a step-by-step manner. Each step is catalyzed by a separate enzyme protein encoded by a specific gene. Most cases of albinism result from changes in one of these enzymes—tyrosinase. The enzyme tyrosinase catalyzes the last step of the pathway, the conversion of tyrosine into melanin.

To perform this task, tyrosinase binds to its substrate, a molecule of tyrosine, and facilitates the molecular changes necessary to produce the pigment melanin. There is a specific “lock-and-key” fit between tyrosine and the active site of the enzyme. The active site is a pocket formed by several crucial amino acids in the polypeptide. If the DNA of the tyrosinase-encoding gene changes in such a way that one of these crucial amino acids is replaced by another amino acid or is lost, then there are several possible consequences. First, the enzyme might still be able to perform its functions but in a less efficient manner. Such a change may have only a small effect at the phenotypic level, so small as to be difficult to observe, but it might lead to a reduction in the amount of melanin formed and, consequently, a lighter skin coloration. Note that the protein is still present more or less intact, but its ability to convert tyrosine into melanin has been compromised. Second, the enzyme might be incapable of any function, in which case the mutational event in the DNA of the gene would have produced an albinism allele, referred to earlier as an a allele. Hence a person of genotype a/a is an albino.

The genotype A/a is interesting. It results in normal pigmentation because transcription of one copy of the wild type allele (A) can provide enough tyrosinase for synthesis of normal amounts of melanin. Genes are termed haplosufficient if roughly normal function is obtained when there is only a single copy of the normal gene. Wild-type alleles commonly appear to be haplosufficient, in part because small reductions in function are not vital to the organism. Alleles that fail to code for a functional protein are called null (“nothing”) alleles and are generally not expressed in combination with func-

tional alleles (in individuals of genotype A/a). The molecular basis of albinism is represented in Figure 1-13. Third, more rarely, the altered protein may perform its function more efficiently and thus be the basis for future evolution by natural selection.

The mutational site in the DNA can be of a number of types. The simplest and most common type is

nucleotide-pair substitution, which can lead to amino acid substitution or to premature stop codons. Small deletions and duplications also are common. Even a single base deletion or insertion produces widespread damage at the protein level; because mRNA is read from one end “in frame” in groups of three, a loss or gain of one nucleotide pair shifts the reading frame, and all the amino acids translationally downstream will be incorrect. Such mutations are called frameshift mutations.

At the protein level, mutation changes the amino acid composition of the protein. The most important

outcomes are change in protein shape and size. Such change in shape or size can result in an absence of biological function (which would be the basis of a null allele) or reduced function. More rarely, mutation can lead to new function of the protein product.

Genetic Variation, Types of Variation

1.2 Genetic variation

If all members of a species have the same set of genes, how can there be genetic variation? As indicated earlier, the answer is that genes come in different forms called alleles. In a population, for any given gene there can be from one to many different alleles; however, because most organisms carry only one or two chromosome sets per cell, any individual organism can carry only one or two alleles per gene. The alleles of one gene will always be found in the same position along the chromosome. Allelic variation is the basis for hereditary variation.

Types of variation

Because a great deal of genetics concerns the analysis of variants, it is important to understand the types of variation found in populations. A useful classification is into discontinuous and continuous variation (Figure 1-10). Allelic variation contributes to both.

DISCONTINUOUS VARIATION Most of the research in genetics in the past century has been on discontinuous variation because it is a simpler type of variation, and it is easier to analyze. In discontinuous variation, a character is found in a population in two or more distinct and separate forms called phenotypes. “Blue eyes” and “brown eyes” are phenotypes, as is “blood type A” or “blood type O.” Such alternative phenotypes are often found to be encoded by the alleles of one gene. A good example is albinism in humans, which concerns phenotypes of the character of skin pigmentation. In most people, the cells of the skin can make a dark-brown or black pigment called melanin, the substance that gives our skin its color ranging from tan color in people of European ancestry to brown or black in those of tropical and sub-tropical ancestry. Although always rare, albinos, who completely lack pigment in their skin and hair, are found in all races (Figure 1-11). The difference between pigmented and unpigmented skin is caused by different alleles of a gene that encodes an enzyme involved in melanin synthesis.

The alleles of a gene are conventionally designated by letters. The allele that codes for the normal form of the enzyme involved in making melanin is called A, and the allele that codes for an inactive form of that enzyme (resulting in albinism) is designated a, to show that they

are related. The allelic constitution of an organism is its genotype, which is the hereditary underpinning of the phenotype. Because humans have two sets of chromosomes in each cell, genotypes can be either A/A, A/a, or a/a (the slash shows that the two alleles are a pair). The phenotype of A/A is pigmented, that of a/a is albino, and that of A/a is pigmented. The ability to make pigment is expressed over inability (A is said to be dominant, as we shall see in Chapter 2).

Although allelic differences cause phenotypic differences such as pigmented and albino coloration, this does not mean that only one gene affects skin color. It is known that there are several, although the identity and number of these genes are currently unknown. However, the difference between pigmented, of whatever shade, and albinism is caused by the difference in the alleles of one gene—the gene that determines the ability to make melanin; the allelic composition of other genes is irrelevant.

In some cases of discontinuous variation, there is a predictable one-to-one relation between genotype and phenotype under most conditions. In other words, the two phenotypes (and their underlying genotypes) can almost always be distinguished. In the albinism example, the A allele always allows some pigment formation, whereas the a allele always results in albinism when present in two copies. For this reason, discontinuous variation has been successfully used by geneticists to identify the underlying alleles and their role in cellular functions.

Geneticists distinguish two categories of discontinuous variation. In a natural population, the existence of two or more common discontinuous variants is called polymorphism (Greek; many forms). The various forms are called morphs. It is often found that different morphs are determined by different alleles of a single gene. Why do populations show genetic polymorphism? Special types of natural selection can explain a few cases, but, in other cases, the morphs seem to be selectively neutral.

Rare, exceptional discontinuous variants are called mutants, whereas the more common “normal” phenotype is called the wild type. Figure 1-12 shows an example of a mutant phenotype. Again, in many cases, the wild-type and mutant phenotypes are determined by different alleles of one gene. Both mutants and polymorphisms originally arise from rare changes in DNA (mutations), but somehow the mutant alleles of a polymorphism become common. These rare changes in DNA may be nucleotide-pair substitutions or small deletions or duplications. Such mutations change the amino acid composition of the protein. In the case of albinism, for example, the DNA of a gene that encodes an enzyme involved in melanin synthesis is changed, such that a crucial amino acid is replaced by another amino acid or lost, yielding a nonfunctioning enzyme. Mutants (such as those that produce albinism) can occur spontaneously in nature, or they can be produced by treatment with mutagenic chemicals or radiation.

Geneticists regularly induce mutations artificially to carry out genetic analysis because mutations that affect some specific biological function under study identify the various genes that interact in that function.

Transcription, Translation And Gene Regulation

TRANSCRIPTION The first step taken by the cell to make a protein is to copy, or transcribe, the nucleotide sequence in one strand of the gene into a complementary single-stranded molecule called ribonucleic acid (RNA). Like DNA, RNA is composed of nucleotides, but these nucleotides contain the sugar ribose instead of deoxyribose. Furthermore, in place of thymine, RNA contains uracil (U), which like thymine, pairs with adenine. Hence the RNA bases are A, G, C, and U. The transcription process, which occurs in the cell nucleus, is very similar to the process for replication of DNA because the DNA strand serves as the template for making the RNA copy, which is called a transcript. The RNA transcript, which in many species undergoes some structural modifications, becomes a “working copy” of the in-formation in the gene, a kind of “message” molecule called messenger RNA (mRNA). The mRNA then enters the cytoplasm, where it is used by the cellular machinery to direct the manufacture of a protein. Fig-ure 1-6 summarizes the process of transcription.

TRANSLATION The process of producing a chain of amino acids based on the sequence of nucleotides in the mRNA is called translation. The nucleotide sequence of an mRNA molecule is “read” from one end of the mRNA to the other, in groups of three successive bases. These groups of three are called codons.

          AUU       CCG      UAC       GUA       AAU       UUG

         codon      codon     codon     codon     codon     codon

Because there are four different nucleotides, there are 4 x 4 x 4 = 64 different codons possible, each one coding for an amino acid or a signal to terminate translation. Because only 20 kinds of amino acids are used in the polypeptides that make up proteins, more than one codon may correspond to the same amino acid. For instance, AUU, AUC, and AUA all encode isoleucine, while UUU and UUC code for phenylalanine, and UAG is a translation termination (“stop”) codon.

Protein synthesis takes place on cytoplasmic organelles called ribosomes. A ribosome attaches to one end of an mRNA molecule and moves along the mRNA, catalyzing the assembly of the string of amino acids that will constitute the primary polypeptide chain of the protein. Each kind of amino acid is brought to the assembly process by a small RNA molecule called transfer RNA (tRNA), which is complementary to the mRNA codon that is being read by the ribosome at that point in the assembly.

Trains of ribosomes pass along an mRNA molecule, each member of a train making the same type of polypeptide. At the end of the mRNA, a termination codon causes the ribosome to detach and recycle to another mRNA. The process of translation is shown in Figure 1-7.

GENE REGULATION Let’s take a closer look at the structure of a gene, which determines the final form of the RNA “working copy” as well as the timing of transcription in a particular tissue. Figure 1-8 shows the general structure of a gene. At one end, there is a regulatory region to which various proteins involved in the regulation of the gene’s transcription bind, causing the gene to be transcribed at the right time and in the right amount. A region at the other end of the gene signals the end point of the gene’s transcription. Between these two end regions lies the DNA sequence that will be transcribed to specify the amino acid sequence of a polypeptide.

Gene structure is more complex in eukaryotes than in prokaryotes. Eukaryotes, which include all the multicellular plants and animals, are those organisms whose cells have a membrane-bound nucleus. Prokaryotes are organisms with a simpler cellular structure lacking a nucleus, such as bacteria. In the genes of many eukaryotes, the protein-encoding sequence is interrupted by one or more stretches of DNA called introns. The origin and functions of introns are still unclear. They are excised from the primary transcript during the formation of mRNA. The segments of coding sequence between the introns are called exons.

Some protein-encoding genes are transcribed more or less constantly; these are the “housekeeping” genes that are always needed for basic reactions. Other genes may be rendered unreadable or readable to suit the functions of the organism at particular times and under particular external conditions. The signal that masks or unmasks a gene may come from outside the cell, for example, from a steroid hormone or a nutrient. Alternatively, the signal may come from within the cell as the result of the reading of other genes. In either case, special regulatory sequences in the DNA are directly affected by the signal, and they in turn affect the transcription of the protein-encoding gene. The regulatory substances that serve as signals bind to the regulatory region of the target gene to control the synthesis of transcripts.

Figure 1-9 illustrates the essentials of gene action in a generalized eukaryotic cell. Outside the nucleus of the cell is a complex array of membranous structures, including the endoplasmic reticulum and Golgi apparatus, and organelles such as mitochondria and chloroplasts. The nucleus contains most of the DNA, but note that mitochondria and chloroplasts also contain small chromosomes.

Each gene encodes a separate protein, each with specific functions either within the cell (for example, the purple-rectangle proteins in Figure 1-9) or for export to other parts of the organism (the purple circle proteins). The synthesis of proteins for export (secretory proteins) takes place on ribosomes that are located on the surface of the rough endoplasmic reticulum, a system of large, flattened membrane vesicles. The completed amino acid chains are passed into the lumen of the endoplasmic reticulum, where they fold up spontaneously to take on their three-dimensional structure. The proteins may be modified at this stage, but they eventually enter the chambers of the Golgi apparatus and from there, the secretory vessels, which eventually fuse with the cell membrane and release their contents to the outside.

Proteins destined to function in the cytoplasm and most of the proteins that function in mitochondria and chloroplasts are synthesized in the cytoplasm on ribosomes not bound to membranes. For example, proteins that function as enzymes in the glycolysis pathway follow this route. The proteins destined for organelles are specially tagged to target their insertion into specific organelles. In addition, mitochondria and chloroplasts have their own small circular DNA molecules. The synthesis of proteins encoded by genes on mitochondrial or chloroplast DNA takes place on ribosomes inside the organelles themselves. Therefore the proteins in mitochondria and chloroplasts are of two different origins: either encoded in the nucleus and imported into the organelle or encoded in the organelle and synthesized within the organelle compartment.

Figure 1-9 Simplified view of gene action in a eukaryotic cell.

The basic flow of genetic information is from DNA to RNA to protein. Four types of genes are shown. Gene 1 responds to external regulatory signals and makes a protein for export; gene 2 responds to internal signals and makes a protein for use in the cytoplasm; gene 3 makes a protein to be transported into an organelle; gene 4 is part of the organelle DNA and makes a protein for use inside its own organelle. Most eukaryotic genes contain introns, regions (generally noncoding) that are cut out in the preparation of functional messenger RNA. Note that many organelle genes have introns and that an RNA-synthesizing enzyme is needed for organelle mRNA synthesis. These details have been omitted from the diagram of the organelle for clarity. (Introns will be explained in detail in subsequent chapters.)

Genes as determinants of the inherent properties of species

1.1 Genes as determinants of the inherent properties of species

What is the nature of genes, and how do they perform their biological roles? Three fundamental properties

are required of genes and the DNA of which they are composed.

1. Replication. Hereditary molecules must be capable of being copied at two key stages of the life cycle

(Figure 1-2). The first stage is the production of the cell type that will ensure the continuation of a

species from one generation to the next. In plants and animals, these cells are the gametes: egg and

sperm. The other stage is when the first cell of a new organism undergoes multiple rounds of division

to produce a multicellular organism. In plants and animals, this is the stage at which the fertilized egg,

the zygote, divides repeatedly to produce the complex organismal appearance that we recognize.

2. Generation of form. The working structures that make up an organism can be thought of as form or substance, and DNA has the essential “information” needed to create form.

3. Mutation. A gene that has changed from one allelic form into another has undergone mutation—an event that happens rarely but regularly. Mutation is not only a basis for variation within a species, but also, over the long term, the raw material for evolution.

We will examine replication and the generation of

form in this section and mutation in the next.

DNA and its replication

An organism’s basic complement of DNA is called its genome. The somatic cells of most plants and animals contain two copies of their genome (Figure 1-3); these

organisms are diploid. The cells of most fungi, algae, and bacteria contain just one copy of the genome; these organisms are haploid. The genome itself is made up of one or more extremely long molecules of DNA that are organized into chromosomes. Genes are simply the regions of chromosomal DNA that are involved in the cell’s production of proteins. Each chromosome in the genome carries a different array of genes. In diploid cells, each chromosome and its component genes are present twice. For example, human somatic cells contain two sets of 23 chromosomes, for a total of 46 chromosomes. Two chromosomes with the same gene array are said to be homologous. When a cell divides, all its chromosomes

(its one or two copies of the genome) are replicated and then separated, so that each daughter cell receives the full complement of chromosomes. 

To understand replication, we need to understand the basic nature of DNA. DNA is a linear, double-helical structure that looks rather like a molecular spiral staircase. The double helix is composed of two intertwined chains made up of building blocks called nucleotides. Each nucleotide consists of a phosphate group, a deoxyribose sugar molecule, and one of four different nitrogenous bases: adenine, guanine, cytosine, or thymine. Each of the four nucleotides is usually designated by the first letter of the base it contains: A, G, C, or T. Each nucleotide chain is held together by bonds between the sugar and phosphate portions of the consecutive nucleotides, which form the “backbone” of the chain. The two intertwined chains are held together by weak bonds between bases on opposite chains (Figure 1-4).

There is a “lock-and-key” fit between the bases on the opposite strands, such that adenine pairs only with thymine and guanine pairs only with cytosine. The bases that form base pairs are said to be complementary. Hence a short segment of DNA drawn with arbitrary nucleotide sequence might be

· · · ·CAGT· · · ·

· · · ·GTCA· · · ·

For replication of DNA to take place, the two strands of the double helix must come apart, rather like

the opening of a zipper. The two exposed nucleotide chains then act as alignment guides, or templates, for the deposition of free nucleotides, which are then joined together by the enzyme DNA polymerase to form a new strand. The crucial point illustrated in Figure 1-5 is that because of base complementarity, the two daughter DNA molecules are identical with each other and with the original molecule.

Generation of form

If DNA represents information, what constitutes form at the cellular level? The simple answer is “protein” because the great majority of structures in a cell are protein or have been made by protein. In this section, we trace the steps through which information becomes form.

The biological role of most genes is to carry information specifying the chemical composition of proteins or the regulatory signals that will govern their production by the cell. This information is encoded by the sequence of nucleotides. A typical gene contains the information for one specific protein. The collection of proteins an organism can synthesize, as well as the timing and amount of production of each protein, is an extremely important determinant of the structure and physiology of organisms.

A protein generally has one of two basic functions, depending on the gene. First, the protein may be a structural component, contributing to the physical properties of cells or organisms. Examples of structural proteins are microtubule, muscle, and hair proteins. Second, the protein may be an active agent in cellular processes—such as an active-transport protein or an enzyme that catalyzes one of the chemical reactions of the cell.

The primary structure of a protein is a linear chain of amino acids, called a polypeptide. The sequence of amino acids in the primary chain is specified by the sequence of nucleotides in the gene. The completed primary chain is coiled and folded—and in some cases, associated with other chains or small molecules—to form a functional protein. A given amino acid sequence may fold in a large number of stable ways. The final folded state of a protein depends both on the sequence of amino acids specified by its gene and on the physiology of the cell during folding.

GENETICS AND THE ORGANISM

Why study genetics? There are two basic reasons. First, genetics occupies a pivotal position in the entire subject of biology. Therefore, for any serious student of plant, animal, or microbial life, an understanding of genetics is essential. Second, genetics, like no other scientific discipline, is central to numerous aspects of human affairs. It touches our humanity in many different ways. Indeed, genetic issues seem to surface daily in our lives, and no thinking person can afford to be ignorant of its discoveries. In this chapter, we take an overview of the science of genetics, showing how it has come to occupy its crucial position. In addition, we provide a perspective from which to view the subsequent chapters.

First, we need to define what genetics is. Some define it as the “study of heredity,” but hereditary phenomena were of interest to humans long before biology or genetics existed as the scientific disciplines that we know today. Ancient peoples were improving plant crops and domesticated animals by selecting desirable individuals for breeding. They also must have puzzled about the inheritance of individuality in humans and asked such questions as “Why do children resemble their parents?”

and “How can various diseases run in families?” But these people could not be called “geneticists.” Genetics as a set of principles and analytical procedures did not begin until the 1860s, when an Augustinian monk named Gregor Mendel (Figure 1-1) performed a set of experiments that pointed to the existence of biological elements that we now call genes. The word genetics comes from the word “gene,” and genes are the focus of the subject. Whether geneticists study at the molecular, cellular, organismal, family, population, or evolutionary level, genes are always central in their studies. Simply stated, genetics is the study of genes.

What is a gene? A gene is a section of a threadlike double-helical molecule called deoxyribonucleic acid, abbreviated DNA. The discovery of genes and the understanding of their molecular structure and function have been sources of profound insight into two of the biggest mysteries of biology:

1. What makes a species what it is? We know that cats always have kittens and people always have babies. This commonsense observation naturally leads to questions about the determination of the properties of a species. The determination must be hereditary

because, for example, the ability to have kittens is inherited by every generation of cats.

2. What causes variation within a species? We can distinguish one another as well as our own pet cat from other cats. Such differences within a species require explanation. Some of these distinguishing features are clearly familial; for example, animals of a certain unique color often have offspring with the same color, and in human families, certain features, such as the shape of the nose, definitely “run in the family.” Hence we might suspect that a hereditary component explains at least some of the variation

within a species.

The answer to the first question is that genes dictate the inherent properties of a species. The products of most genes are specific proteins. Proteins are the main macromolecules of an organism. When you look at an organism, what you see is either a protein or something that has been made by a protein. The amino acid sequence of a protein is encoded in a gene. The timing and rate of production of proteins and other cellular components are a function both of the genes within the cells and of the environment in which the organism is developing and functioning.

The answer to the second question is that any one gene can exist in several forms that differ from one another, generally in small ways. These forms of a gene are called alleles. Allelic variation causes hereditary variation within a species. At the protein level, allelic variation becomes protein variation.

The next sections of this chapter show how genes influence the inherent properties of a species and how

allelic variation contributes to variation within a species. These sections are an overview; most of the details will be presented in later chapters.

جتنی دیر میں آپ یہ تحریر پڑھیں گے اتنی دیر میں فیسبک

جتنی دیر میں آپ یہ تحریر پڑھیں گے اتنی دیر میں فیسبک کے ڈیٹا سینٹرز میں 33 ہزار گیگا بائٹس پر مشتمل ڈیٹا کا اضافہ ہو چکا ہو گا۔ جن میں سے دو میگا بائیٹس آپ کے بھی ہوں گے۔ فیسبک پر روزانہ تقریباً چار پیٹا بائٹس ڈیٹا جمع ہوتا ہے۔ یہ جاننے کے لیے کہ ایک پیٹا بائٹ میں کتنا ڈیٹا ہوتا ہے یوں سمجھ لیجیے کہ اگر آپ ایک مکمل ایچ ڈی ویڈیو چوبیس گھنٹے ریکارڈ کریں اور یہ ریکارڈنگ مسلسل ساڑھے تین سال تک جاری رہے تب جا کر ایک پیٹا بائٹ ڈیٹا بنے گا۔

قارئین گیگا بائٹس سے تو ضرور واقف ہوں گے۔ ایک پیٹا بائٹس میں دس لاکھ گیگا بائٹس ہوتے ہیں۔ اتنے بڑے پیمانے پر پیدا ہونے والے ڈیٹا کو محفوظ رکھنے کے لیے فیسبک کے پاس سینکڑوں ایکڑ پر محیط چھ سے زائد بڑی عمارات ہیں۔ جنہیں ڈیٹا سینٹرز کہا جاتا ہے۔ ان عمارتوں میں بے شمار بڑے بڑے ریک ہیں۔ اور ہر ریک میں بیسیوں ڈیٹا سرورز ہیں۔ ایک اندازے کے مطابق اب تک فیسبک کے پاس تقریباً تیس ہزار سے زائد ڈیٹا سرورز ہیں۔ اور ہر گذرتے دن کے ساتھ ان کی تعداد میں اضافہ ہو رہا ہے۔ یہ سرورز چوبیس گھنٹے انٹرنیٹ سے جڑے رہتے ہیں۔ انہیں توانائی فراہم کے لیے بڑے بڑے جنریٹرز اور ٹھنڈا رکھنے کے لیے باقاعدہ کولنگ کے نظاموں کی تنصیب کی گئی ہے۔ سینکڑوں ایکڑ پر محیط ان عمارتوں کا سلسلہ اب دراز ہوتا جا رہا ہے۔ یہ مراکز اب امریکہ سے باہر دیگر ممالک میں بھی قائم کیے جا رہے ہیں۔ اور ان میں ہر روز پیٹا بائٹس کا اضافہ ہو رہا ہے۔

مجھے یقین ہے کہ اس سب کے سامنے آپ کو اپنے دو میگا بائیٹس بہت حقیر معلوم ہو رہے ہوں گے۔ لیکن یہ دو ایم بی آپ کا سب کچھ ہیں۔ آپ کا دماغ ہیں۔ وہ دماغ جو آپ خود اپنے ہاتھوں سے گروی رکھوا رہے ہیں۔ آپ کی شناخت، آپ کی شخصیت، آپ کی نفسیات، حتی کہ آپ کے خیالات بھی۔ بات اگر ڈیٹا محفوظ رکھنے کی حد تک ہوتی تو اور بات تھی لیکن ان بڑے بڑے جناتی ڈیٹا سینٹرز میں پچیدہ ترین الگورتھز بھی کام کر رہے ہیں۔ جو آپ کی جانب سے پیدا کیے گئے ڈیٹا کی جانچ کرتے ہیں اور پھر اسی کی مناسبت سے آپ کی شخصیت کا تعین کرتے ہیں۔ آپ کے دو ایم بی میں آپ کے لائیک، کمنٹ، سرچ اور جو کام آپ فیسبک پر کر رہے ہیں وہ سب شامل ہوتا ہے۔

ہو سکتا ہے آپ کہیں کہ میں تو فیسبک پر لائیک کمنٹ کرتا ہی نہیں۔ میرے بارے میں کیسے جان لے گی؟ تو حضرت آپ اکاؤنٹ بنانے کے بعد پورا سال فیسبک پر کسی ایک پوسٹ کو بھی لائیک، کمنٹ نہ کیجیے۔ تب بھی یہ ایپ جانتی ہے کہ آپ اس دوران کیا کیا کرتے رہے۔ آپ کیا شوق سے پڑھتے ہیں۔ آپ کو کیا پسند ہے کیا نہیں۔ یہاں تک کہ آپ فیسبک کے علاوہ کیا کیا کچھ دیکھتے رہتے ہیں۔ نہیں یقین آ رہا؟ تو ابھی فیسبک اکاؤنٹ سیٹنگز میں جا کر فیسبک سے باہر کی سرگرمی یعنی
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پر کلک کیجیے۔ اور دیکھیے کہ آپ فیسبک کے علاوہ اپنے موبائل سے کیا کرتے رہتے ہیں۔ اگر ایسے پتہ نہ چلے تو آپ ڈاؤنلوڈ مائی ایکٹیویٹی کے ذریعے تمام معلومات کو ایک فائل کہ صورت ڈاؤنلوڈ کر کے بھی دیکھ سکتے ہیں۔ یاد رہے یہ تو محض ایک جھلک ہے کہ فیسبک ایپ سے ہٹ کر آپ کے بارے میں کیا جانتی ہے۔ اصل میں کیا کچھ جانتی ہے ہم سوچ بھی نہیں سکتے۔

آپ گوگل سرچ کا استعمال نہیں کرتے۔ کوئی گیم نہیں کھیلتے۔ کچھ بھی نہیں کرتے۔ بس موبائل کو انٹرنیٹ آف کیے گھومتے رہتے ہیں کہ کبھی کبھار آن کر کے کوئی پوسٹ دیکھ لیں گے تب بھی آپ کی لوکیشن سمیت بہت سارا ڈیٹا اس کے ڈیٹا سینٹر میں اپڈیٹ ہو چکا ہو گا۔ حال اور مستقبل کو چھوڑیے، میں نے جن عمارتوں کا اوپر تذکرہ کیا ہے ان میں ایک ایسی عمارت ہے جسے ڈیٹا کا کولڈ اسٹور بھی کہا جاتا ہے۔ یہ وہ جگہ ہے جہاں آپ کا اور ہمارا ماضی پڑا ہے۔ دس سال پرانی معلومات بھی موجود ہیں۔ یہاں کے سرور عموماً سوئے رہتے ہیں۔ اور تب جاگتے ہیں جب ہم ماضی میں دیکھنا چاہیں۔ لیکن الگورتھم یہاں بھی کام کرتے رہتے ہیں۔ وہ نہیں سوتے۔ کیونکہ وہ ہمیں ٹریک کر رہے ہیں۔

فیسبک کو ایک طرف رکھیں گوگل، مائیکروسافٹ، ایپل تمام بڑے ادارے ہمیں ہمہ وقت ٹریک کر رہے ہیں۔ ہماری آن اور آف لائن ایکٹیویٹی ان کی نظر میں۔۔۔۔۔ میگا چھوڑ گیگا بائٹس کی شکل میں ہمارا ڈیٹا ان کے پاس پڑا ہے۔ اور مسلسل بڑھ رہا ہے۔
روندے چِپاں نوں۔۔۔۔۔

حضرات آپ کی شخصیت، خیالات اور رجحانات جاننے کے لیے بل گیٹس کو آ کر آپ کے اندر چِپ منتقل کرنے کی کوئی ضرورت نہیں۔ نہ ہی عالمی سطح کا ڈرامہ کھڑا کرنے کی ضرورت۔۔۔۔ وہ یہ کام پہلے ہی کر رہے ہیں۔ اور جہاں تک کنٹرول کرنے کی بات ہے تو یہ آپ کی بھول ہے کہ آپ آزادی سے سوچتے ہیں۔ بھیڑچال، ٹرینڈنگ اور میڈیا پروپیگنڈے کے اس دور میں آپ وہی سوچتے ہیں جو وہ چاہتے ہیں۔ اور وہی کرتے ہیں جو وہ کروانا چاہتے ہیں۔ یہ بات مبالغہ آرائی لگتی ہو گی۔ لیکن میرا مشورہ ہے کہ ایک بار حالیہ تاریخ میں سامنے آنے والے کیمرج اینالاٹیکا سمیت دیگر فیسبک اسکینڈلز کا مطالعہ کر لیں۔ ہلکا سا اندازہ ہو جائے گا کہ میری بات میں کتنی مبالغہ آرائی ہے۔ یہ جو سازشی نظریات گھڑے جاتے ہیں یہ بھی وہیں سے درآمد شدہ اور جان بوجھ کر پھیلائے جاتے ہیں۔ نہ یقین آئے تو بل گیٹس کے حوالے سے حالیہ افواہوں کے بعد اس کی فاؤنڈیشن کی پہلے سے بڑھتی اہمیت پر سرچ کر لیجیے۔ آٹے دال کا بھاؤ معلوم ہو جائے گا۔ ان اداروں کا وہی حال ہے کہ بدنام ہوں گے تو کیا نام نہ ہو گا؟
اور بدقسمتی سے ہم اپنی دانست میں انہیں بدنام کرنے کے چکر میں مزید نام دے رہے ہیں۔

اب یہاں سوال پیدا ہوتا ہے۔ کہ ہم کیا کریں۔ ہمیں باہر سے آنے والے سازشی نظریات پر آنکھیں بند کر کے یقین کرنے کی بجائے حقیقت کو سمجھنا ہو گا۔ اور حقیقت یہ ہے کہ جدید دور میں ہماری حیثیت ایک "ڈیجیٹل اینٹٹی" سے بڑھ کر نہیں ہے۔ اس حقیقت کو تسلیم کرتے ہوئے ہمیں اپنے مقام کو منوانا ہو گا۔ ہائے ہائے کرنے کی بجائے اپنے آپ کو اپگریڈ کریں۔ اس قابل کریں کہ آپ جدید دور کے جدید تقاضوں سے ہم آہنگ ہو سکیں۔ یہی وقت کی ضرورت ہے۔ جان رکھیں کہ آپ کے اندر سے ایمان کی جین نکالنے کے لیے کسی کو چِپ ڈالنے کی کوئی ضرورت نہیں۔ چند لائیکس اور کمنٹس کی خاطر اپنا ایمان بیچ ڈالنے والوں کے لیے کرونا جیسی عالمی وباء پیدا کرنے کی کسے ضرورت ہے؟

شتر مرغ کی طرح ریت میں سر دبا لینے سے کچھ نہیں ہو گا۔ اپنے اندر ہمت پیدا کیجیے۔ اپنے آپ کو اس قابل کیجیے کہ دنیا آپ کی چوکھٹ پر دستک دے۔ ایک دن فیسبک بند ہو جائے تو لوگ ٹکریں مارتے پائے جاتے ہیں۔ ہم خود کیوں نہیں اس قابل ہو جاتے کہ اپنے آپ کو ڈیجیٹل دور کے مطابق ڈھال لیں۔ خود میں جدت لا کر، تحقیق و دریافت کے ذریعے ڈرائیونگ سیٹ سنبھال لیں۔ ہم اکیسویں صدی کے تیسرے عشرے میں داخل ہو چکے ہیں۔ بغیر ڈرائیور ہائبرڈ اور اڑتی کاریں چند قدم کے فاصلے پر ہیں۔ فائیو جی، اشیائی انٹرنیٹ اور ورچول ریالٹی (مجازی حقیقت) دروازے پر دستک دے رہی ہے۔ ریموٹ ورکنگ اور ٹیلی تفریح کا رجحان فروغ پا رہا ہے۔ مصنوعی ذہانت انقلاب برپا کرنے کو ہے۔ جلد یا بدیر ان چیزوں کو اپنانا ہی پڑے گا۔ تو پھر کیوں نہ آج اور ابھی سے اس کی یوں ابتداء کی جائے کہ سائنس و ٹیکنالوجی پر تحقیق کا میدان ہمارے تصرف میں ہو؟

طویل تحریر کے لیے معذرت کیونکہ ہمیں حقیقت سے روشناس کرواتی طویل تحریریں پڑھنے کی عادت نہیں جبکہ سازشی نظریات پر لکھی لمبی لمبی تحریریں پڑھنے کا شوق ہے۔ حالانکہ سازشی نظریات گھڑنے والوں کی مثال اس شخص کی سی ہے جو سارا سال نشہ کیے سوتا رہے اور جب بھی کوئی اہم معاملہ ہو تو اسے سازشِ اغیار کے کھاتے میں ڈال کر پھر سے آنکھیں موند لے۔

آخر میں یہی کہوں گا کہ زمانے کی چال سے آگے نہیں بڑھ سکتے تو آنکھیں موند کر پیچھے بھی نہ رہیے۔ ساتھ چلنے کی ہمت پیدا کیجیے۔ اپنا اور اپنوں کا خیال رکھیے۔

(اعدادوشمار کئی ویب سائٹس اور آفیشل ذرائع سے حاصل کرنے کے بعد اندازاً اور مجموعی اوسط میں پیش کیے گئے ہیں۔ اس سے کم یا کہیں زیادہ بھی ہو سکتے ہیں۔)
منقول

اس دنیا میں ہر شخص اپنےٹائم زون کی بنیاد پر کام کر رہا ہے

پریشان نہ ہوں ۔۔

کچھ لوگ اپنی تعلیم 22 سال کی عمر میں مکمل کر لیتے ہیں۔ مگر ان کو پانچ پانچ سال تک کوئی اچھی نوکری نہیں ملتی۔

کچھ لوگ 25 سال کی عمر میں کسی کپمنی کے CEO بن جاتے ہیں اور 50 سال کی عمر میں ہمیں پتہ چلتا ہے انکا انتقال ہو گیا ہے۔

جبکہ کچھ لوگ 50 سال کی عمر میں CEO بنتے ہیں اور نوے سال تک حیات رہتے ہیں۔

بہترین روزگار ہونے کے باوجود کچھ لوگ ابھی تک غیر شادی شدہ ہیں اور کچھ لوگ بغیر روزگار کے بھی شادی کر چکے ہیں اور روزگار والوں سے زیادہ خوش ہیں۔

اوبامہ 55 سال کی عمر میں ریٹائر ہو گیا جبکہ ٹرمپ 70 سال کی عمر میں شروعات کرتا ہے۔۔۔

کچھ لیجنڈ امتحان میں فیل ہونے پر بھی مسکرا دیتے ہیں اور کچھ لوگ 1 نمبر کم آنے پر بھی رو دیتے ہیں۔۔۔۔

Time zone اس دنیا میں ہر شخص اپنے

کی بنیاد پر کام کر رہا ہے۔ ظاہری طور پر ہمیں ایسا لگتا ہے کچھ لوگ ہم سے بہت آگے نکل چکے ہیں اور شاید

ایسا بھی لگتا ہو کچھ ہم سے ابھی تک پیچھے ہیں لیکن ہر شخص اپنی اپنی جگہ ٹھیک ہے اپنے اپنے وقت کے مطابق۔ ان سے حسد مت کیجئے۔ اپنے اپنے میں رہیں۔۔ Time zone

کسی کو بغیر کوشش کے بھی بہت کچھ مل گیا اور کچھ ساری زندگی بس ایڑیاں ہی رگڑتے رہے۔۔

انتظار کیجئے اور اطمینان رکھیئے۔

نہ ہی آپ کو دیر ہوئی ہے اور نہ ہی جلدی۔

اللہ رب العزت جو کائنات کا سب سے عظیم الشان ہے اس نے ہم سب کو اپنے حساب سے ڈیزائن کیا ہے وہ جانتا ہے کون کتنا بوجھ اٹھا سکتا . کس کو کس وقت کیا دینا ہے. اپنے آپ کو رب کی رضا کے ساتھ باندھ دیجئے اور یقین رکھیئے کہ اللہ کی طرف سے آسمان سے ہمارے لیے جو فیصلہ اتارا جاتا ہے وہ ہی بہترین ہے۔۔۔

❤️❤️ سو اچھی اچھی باتیں ❤️❤️

❤️❤️ سو اچھی اچھی باتیں  ❤️❤️

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دوسروں کی غلطیاں معاف کر دیا کرو⧭

لوگوں کے ساتھ آہستہ بولا کرو⧭

اپنی آواز نیچی رکھا کرو⧭

دوسروں کا مذاق نہ اڑایا کرو⧭

والدین کی خدمت کیا کرو⧭

منہ سے والدین کی توہین کا ایک لفظ نہ نکالو⧭

والدین کی اجازت کے بغیر ان کے کمرے میں داخل نہ ہوا کرو⧭

حساب لکھ لیا کرو⧭

کسی کی اندھا دھند تقلید نہ کرو⧭

اگر مقروض مشکل وقت سے گزر رہا ہو تو اسے ادائیگی کے لیے مزید وقت دے دیا کرو⧭

سود نہ کھاؤ⧭

رشوت نہ لو⧭

وعدہ نہ توڑو⧭

دوسروں پر اعتماد کیا کرو⧭

سچ میں جھوٹ نہ ملایاکرو⧭

لوگوں کے درمیان انصاف قائم کیا کرو⧭

انصاف کے لیے مضبوطی سے کھڑے ہو جایا کرو⧭

مرنے والوں کی دولت خاندان کے تمام ارکان میں تقسیم کیاکرو⧭

خواتین بھی وراثت میں حصہ دار ہیں⧭

یتیموں کی جائیداد پر قبضہ نہ کرو⧭

یتیموں کی حفاظت کرو⧭

دوسروں کا مال بلا ضرورت خرچ نہ کرو⧭

لوگوں کے درمیان صلح کراؤ⧭

بدگمانی سے بچو⧭

غیبت نہ کرو⧭

جاسوسی نہ کرو⧭

خیرات کیا کرو⧭

غرباء کو کھانا کھلایا کرو⧭

ضرورت مندوں کو تلاش کر کے ان کی مدد کیا کرو⧭

فضول خرچی نہ کیا کرو⧭

خیرات کر کے جتلایا نہ کرو⧭

مہمانوں کی عزت کیاکرو⧭

نیکی پہلے خود کرو اور پھر دوسروں کو تلقین کرو⧭

زمین پر برائی نہ پھیلایا کرو⧭

لوگوں کو مسجدوں میں داخلے سے نہ روکو⧭

صرف ان کے ساتھ لڑو جو تمہارے ساتھ لڑیں⧭

جنگ کے دوران جنگ کے آداب کا خیال رکھو⧭

جنگ کے دوران پیٹھ نہ دکھاؤ⧭

مذہب میں کوئی سختی نہیں⧭

تمام انبیاء پر ایمان لاؤ⧭

حیض کے دنوں میں مباشرت نہ کرو⧭

بچوں کو دو سال تک ماں کا دودھ پلاؤ⧭

جنسی بدکاری سے بچو⧭

حکمرانوں کو میرٹ پر منتخب کرو⧭

کسی پر اس کی ہمت سے زیادہ بوجھ نہ ڈالو⧭

نفاق سے بچو⧭

کائنات کی تخلیق اور عجائب کے بارے میں گہرائی سے غور کرو⧭

عورتیں اور مرد اپنے اعمال کا برابر حصہ پائیں گ⧭

منتخب خونی رشتوں میں شادی نہ کرو⧭

مرد کو خاندان کا سربراہ ہونا چاہیے⧭

بخیل نہ بنو⧭

حسد نہ کرو⧭

ایک دوسرے کو قتل نہ کرو⧭
فریب (فریبی) کی وکالت نہ کرو⧭
گناہ اور شدت میں دوسروں کے ساتھ تعاون نہ کرو⧭
نیکی میں ایک دوسری کی مدد کرو⧭
اکثریت سچ کی کسوٹی نہیں ہوتی⧭
صحیح راستے پر رہو⧭
جرائم کی سزا دے کر مثال قائم کرو⧭
گناہ اور ناانصافی کے خلاف جدوجہد کرتے رہو⧭
مردہ جانور‘ خون اور سور کا گوشت حرام ہے⧭
شراب اور دوسری منشیات سے پرہیز کرو⧭
جواء نہ کھیلو⧭
ہیرا پھیری نہ کرو⧭
چغلی نہ کھاؤ⧭
کھاؤ اور پیو لیکن اصراف نہ کرو⧭
نماز کے وقت اچھے کپڑے پہنو⧭
آپ سے جو لوگ مدد اور تحفظ مانگیں ان کی حفاظت کرو‘ انھیں مدد دو⧭
طہارت قائم رکھو⧭
اللہ کی رحمت سے کبھی مایوس نہ ہو⧭
اللہ نادانستگی میں کی جانے والی غلطیاں معاف کر دیتا ہے⧭
لوگوں کو دانائی اور اچھی ہدایت کے ساتھ اللہ کی طرف بلاؤ⧭
کوئی شخص کسی کے گناہوں کا بوجھ نہیں اٹھائے گا⧭
غربت کے خوف سے اپنے بچوں کو قتل نہ کرو⧭
جس کے بارے میں علم نہ ہو اس کا پیچھا نہ کرو⧭
پوشیدہ چیزوں سے دور رہا کرو (کھوج نہ لگاؤ)⧭
اجازت کے بغیر دوسروں کے گھروں میں داخل نہ ہو⧭
اللہ اپنی ذات پر یقین رکھنے والوں کی حفاظت کرتا ہے⧭
زمین پرعاجزی کے ساتھ چلو⧭
دنیا سے اپنے حصے کا کام مکمل کر کے جاؤ⧭
اللہ کی ذات کے ساتھ کسی کو شریک نہ کرو⧭
ہم جنس پرستی میں نہ پڑو⧭
صحیح(سچ) کا ساتھ دو‘ غلط سے پرہیز کرو⧭
زمین پر ڈھٹائی سے نہ چلو⧭
عورتیں اپنی زینت کی نمائش نہ کریں⧭
اللہ شرک کے سوا تمام گناہ معاف کر دیتا ہے⧭
اللہ کی رحمت سے مایوس نہ ہو⧭
برائی کو اچھائی سے ختم کرو⧭
فیصلے مشاورت کے ساتھ کیا کرو⧭
تم میں وہ زیادہ معزز ہے جو زیادہ پرہیزگار ہے⧭
مذہب میں رہبانیت نہیں⧭
اللہ علم والوں کو مقدم رکھتا ہے⧭
غیر مسلموں کے ساتھ مہربانی اور اخلاق کے ساتھ پیش آؤ⧭
خود کو لالچ سے بچاؤ⧭
اللہ سے معافی مانگو‘ یہ معاف کرنے اور رحم کرنے والا ہے⧭
’’جو شخص دست سوال دراز کرے اسے انکار نہ کرو‘‘⧭

*اللہ عمل کرنے کی توفیق عطا فرمائے آمین ثم آمیـــــــــــــن یا رب العالمین