eChapters

Tandem Selection
Selection is practiced for one trait at a time until satisfactory improvement has been achieved in this trait. Then, selection efforts for this trait are relaxed and efforts are directed towards the improvement of a second, then for a third and so on, until finally each trait has been improved to the desired level. This method is the least efficient of all the three methods, from the stand point of the amount of genetic progress made for the time and effort by the breeder. Efficiency of tandem selection depends a great deal upon the genetic correlation between the traits selected for. If the genetic correlation is positive and desirable, improvement in one trait by selection would automatically result in improvement in the other trait not selected for, and then the method could be quite efficient. Otherwise, if there were little or no genetic correlation between the traits, which means that they are inherited independently, the efficiency would be less. When the two traits are negatively correlated, improvement in one trait is nullified or neutralized by the regression in the other. For example, in poultry, selection for egg number will result in reduction in egg weight, as they are negatively correlated.
Independent Culling Level (ICL) Method
Method of selecting two or more traits but they both need to meet a minimum standard. It is very strict that if the animal didn’t meet one trait it would be rejected. Independent Culling level (ICL) Method selects several characteristics or traits simultaneously.
Breeders set minimum or maximum culling levels or standards or criteria for each trait of selection objectives. Any animal not meeting all criteria is not selected for use in the breeding program regardless of the level of excellence of other traits. With each successive generation of progeny, the minimum quality of each characteristic is raised thus ensuring improvement of these traits. For example, a breeder has a view of the minimum requirements for milk yield, fat yield, and service period for which cows are breeding. The breeder will determine what the minimum acceptable quality for each of these traits will be for progeny to be folded back into her breeding program. Any animal that fails to meet the quality threshold for any one of these criteria is culled from the breeding program. Thereby, it causes the loss of excellent genes from the population for a particular trait.

Thus the average value of progeny genotypes in response to selection of parental phenotypes depends largely on Cov (G, g), the genetic covariance of parent and offspring which is half the additive genetic variance of the parents.
We know that on an average, half of genes of a parent are passed to the offspring and with them a random half of his additive merit. One-fourth of his additive x additive gene combinations are also transmitted and lesser fractions of higher additive combinations. No dominance combinations are transmitted, since only one member of each allelic gene pair reaches the offspring. Similarly all epistatic gene combinations involving allelic gene pairs are broken up at gamete formation. If dominance and epistatic gene combinations involving allelic gene pairs are important in determining genetic superiority for the trait, then direct selection of superior parents will not produce genetically superior offspring. Some form of mating system which will recreate these combinations in the offspring, together with the formation of lines or groups within the population is needed in these circumstances.
Thus, the aim of selection is to identify and select as parents individuals with high additive genetic merit. By selecting the parent on additive merit, we also ensure that a fraction of any parallel merit for additive type epistasis is also passed on. In considering response to selection, little is lost by treating the response as if it were wholly determined by the additive effects of genes

1. Individual or mass selection
The terms individual selection and mass selection are often used interchangeably, and they refer to selection solely based on the individual´s phenotype. This is a well-known and widely used method of selection in animal breeding. It can be used on characteristics that can be measured in the candidate animal itself, as weight gain is most efficient in characteristics of high heritability. Individual selection is usually the simplest method to operate and, in many circumstances, it yields the most rapid response. It does not require individual identification or the maintenance of pedigree records, hence, it may be considered the least costly method. In principle, it can produce rapid improvement if the heritability of the trait(s) under selection is high. It can be suitable for growth rate and morphological traits (easily assessed, expressed in both sexes). By contrast, individual selection is not suitable for situations in which the estimation of breeding values requires the slaughter of the animals (carcass and flesh quality traits). When applying individual selection, the evaluated animals must be under equal environmental conditions; therefore, the environmental conditions must be controlled. In this case, the influence of external conditions should be minimal and kept the same for all individuals to be compared at any life cycle stage. In this manner, the probability of correct ranking of the individuals based on thus genetic merit is maximized. Differences between individuals or groups of individuals for environmental factors may reduce the accuracy of the selection substantially, and in that way, can also reduce the possibility for genetic improvement. it is important to form contemporary groups and select within them. To obtain as equal environmental conditions as possible all individuals to be compared should be reared under identical environmental conditions. Therefore, it is important to form groups of animals with similar ages, grown in the same production systems, with similar control of environment, handling, and feeding. However, mass selection may be unsuitable if there is large uncontrolled systematic environmental variation (for example age differences). Additionally, there is no control of inbreeding with mass selection.

Natural Selection
In nature, the main force responsible for selection is of interest because of its apparent effectiveness and because of principles involved. Some of the most interesting cases of natural selection are those involving man himself. All races of man that now exist belong to the same species, because the races are interfile or have been in all instances where mating have been made between them. All races of man now in existence had a common origin and at one time probably all man had the some kind of skim pigmentation – which kind we have no sure way of knowing. As the number of generations of man increased, mutations occurred in the genes affecting pigmentation of the skin causing genetic variations in this trait over a range from light to dark or black.
Natural selection is a very complicated process and many factors determine the proportion of individuals that will reproduce. Among these factors are differences in mortality of the individuals in the population especially early in life, differences in the duration of the period of sexual activity and in the degree of sexual activity itself and the differences in the degree of fertility of individuals in the population. They are also examples of adaptive evolution.

Weaning to 210 days: Weight in kg of feed consumed for producing one kg of live weight for the period from weaning to 210 days of age.
10 Mortality percentages (as percentage)
Pre-weaning mortality: No. of piglets died during the period birth to weaning (28/56 days) the number of piglets born alive.
Post weaning mortality: Number of piglets died during the period from 28/56th to 365 day to the total number of piglets available at weaning.
Adult mortality: Number of adult pigs died to the number started at one year (in percentage).
List of registers to be maintained:
• Birth register
• Youngstock register
• Adult stock register
• Disposal register
• Mortality register
• Weighment register
• Farrowing and growth record
• Service register
• Boar performance register
• Sow performance register
• Veterinary register
• Feed efficiency register
• Account register

Types of Breeds
Domestic cattle belong to the family Bovidae, sub-family Bovinae and can be classified into Bos Taurus and Bos indicus. They have 30 pairs of chromosomes, interbreed and are distributed throughout the tropics. The domestication of Bos taurus cattle took place some 8000to 9000 years ago and Hamitic longhorn and shorthorn types are believed to be their ancestors. The origin of Bos indicus breeds (humped cattle) were in western Asia. Both humped and hump less cattle were introduced to Africa from western Asia and into America and Australia from Europe by the immigrants. The European cattle Bos taurus were introduced in the tropics to be raised as pure-bred sand crossbred with indigenous breeds. As a result of crossing of native cattle with European dairy breeds, large numbers of crossbreeds have been produced in various tropical countries, which are being used in selection programs. Zebu Bos indicus cattle were introduced into United States in the nineteenth century for crossbreeding with European breeds. Breeds resulting from crosses are used in the southern regions of North America and tropical South America. Most of the cattle breed in the tropics evolved, through natural selection, for adaptability and survival to local environments. Often, breeds resemble each other with slight morphological differences, but because of constant inbreeding in one locality, independent breeds have evolved. In general, the cattle from drier regions are well built and those from heavy rainfall areas, coastal and hilly regions are of smaller build.
Classification of Cattle Breeds
Most indigenous cattle breeds in the tropics are multipurpose (milk, meat, draught) and that only a few breeds have good milk potential. Physical and economic parameters for some of the important indigenous dairy breeds and new crossbred types developed in the tropics are discussed. Indian cattle breeds of cattle are classified in to three types as under: a) Milch breeds: b) Dual Purpose breeds: c) Draught breeds

Definition of Animal Breeding
Animal breeding, as the application of science to the genetic improvement of animals, implies a close inter relationship between theory and its application. Genetics has provided the matrix form which logical principles could be developed and tested by experimentation and practice.
During the 20th century, genetics has assumed a broader meaning and numerous subdivisions of the discipline has emerged. Advances in animal breeding also have drawn heavily on contributions from statistics, biochemistry, physiology, economics and other disciplines. Animal breeding and reproductive physiology have been uniquely interwoven.
Animals with superior genotypes cannot contribute to succeeding generations unless their reproductive capacity is maintained at satisfactory levels.
Livestock production is an economic enterprise. Hence, animal breeding recommendations must withstand the scrutiny of economic, as well as genetic considerations, before they are accepted and integrated into enterprises by breeders. As a consequence, a close relationship between the breeder and the science, application and theory has been nurtured.
History of Animal Breeding
• Till 500 A.D. when the fall of Roman Empire began animal breeding was at its esteem. Withthe fall of Roman Empire for about 1000 years called Dark and Middle Ages, animal husbandry was at a still.
• From 1700 A.D., again there was an improvement. The beginning of modern animal breeding is to be found mainly in England and Europe.
• The British Royalty encouraged horse breeding especially for race horses. The Earls and Dukes imported bulls from Holland and bred their native stocks. Dutch cattle were introduced into Hereford shire that laid the foundation of the present Hereford cattle. By crossing the native and Dutch cattle and subsequent inbreeding, the British cattle were improved far beyond the best.

In genetic studies it is necessary to distinguish two causes of correlation is chefly pleiotropy, though linkage is a cause of transient correlation, particularly in populations derived from crosses between divergent strains. Pleiotropy is simply the property of a gene whereby it affects two or more characters, so that if the gene is segregating it causes simultaneous variation in the characters is affects. For example, genes that increase growth rate increase both stature and weight, so that they tend to cause correlation between these two characters. The degree of correlation arising from pleiotropy expresses the extent to which two characters are influenced by the same genes. But the correlation resulting from pleiotropy is the overall, or net, effect of all the segregating genes that affect both characters. Some genes may increase both characters, while others increase one and reduce the other the former tend to cause a positive correlation the latter a negative one. So pleiotropy does not necessarily cause a detectable correlation. The correlation resulting from environmental causes is the overall effect of all the environmental factors that vary; some may tend to cause a positive correlation, others a negative one.
Genetic correlation
Hazel (1943) introduced this statistic and is defined as the correlation between the additive genetic values of two traits. When two traits are considered together we have three population parameters:

There are two assumptions necessary involved in the regression of repeatability. These are:
• The variances of the different measurements are equal and have their components in the same proportions, and
• The different measurements reflect genetically the same character. If these assumptions are not valid the repeatability concept becomes vague without precise meaning in relation to the variance components.
The repeatability differs very much depending on the following:
• The nature of the trait.
• The genetic properties of the population.
• Environmental conditions under which the individuals are kept or raised.
Repeatability indicates the proportion of observed differences in performance between animals caused by differences in real producing ability. That is say, repeatability of butterfat yield is 0.40, and if a cow has an age corrected butter fat yield of 30 kilograms above the herd average, her near producing ability will be equal to 30x 0.40 = 12 kg. above the herd average. This can also be explained in a different way, i.e., if two cows differ in one lactation by 30 kg in butter fat yield. They will have difference of 12 kg of butter fat in the next lactation.
Repeatability has a value 0 to 1 and may also be expressed in percentage. Repeatability of a trait is not a constant, and measurements error or generally, varying environmental conditions tend to increase VEt and thus to decrease repeatability, shrode et al (1960) have shown the effect of a change in environmental conditions on repeatability. They obtained repeatabilities of milk yield, butter fat yield and fat percentage as 0.37, 0.32 and 0.7 respectively and after improving the management removed some of the environmental variations that had marked the cows real producing abilities.

Heritability measures the fraction of phenotype variability that can be attributed to genetic variation. This is not the same as saying that this fraction of an individual phenotype is caused by genetics. For example, it is incorrect to say that since the heritability of personality traits is about 0.6, that means that 60% of your personality is inherited from your parents and 40% comes from the environment. In addition, heritability can change without any genetic change occurring, such as when the environment starts contributing to more variation. As a case in point, consider that both genes and environment have the potential to influence intelligence. Heritability could increase if genetic variation increases, causing individuals to show more phenotypic variation, like showing different levels of intelligence. On the other hand, heritability might also increase if the environmental variation decreases, causing individuals to show less phenotypic variation, like showing more similar levels of intelligence. Heritability increases when genetics are contributing more variation or because non-genetic factors are contributing less variation; what matters is the relative contribution. Heritability is specific to a particular population in a particular environment. High heritability of a trait, consequently, does not necessarily mean that the trait is not very susceptible to environmental influences.Heritability can also change as a result of changes in the environment, migration, inbreeding, or the way in which heritability itself is measured in the population under study. The heritability of a trait should not be interpreted as a measure of the extent to which said trait is genetically determined in an individual.
The extent of dependence of phenotype on environment can also be a function of the genes involved. Matters of heritability are complicated because genes may canalize a phenotype, making its expression almost inevitable in all occurring

Individuals in a population can vary considerably on physical, cognitive, and behavioural traits. Examples include height, weight, intelligence, personality, etc. Individual differences may arise from variation in genes, environmental experiences, or a combination of both. It is generally accepted that individual differences in most traits are due to both genetic and environmental factors. To the extent that a trait is influenced by genetic (heritable) effects, phenotypic similarity is correlated with genetic relatedness.
The degree of resemblance among relatives allows for the estimation of genetic variance as well as heritability of a trait. We will now focus on how phenotypic correlation of relatives can be used to estimate the relative magnitude of genetic and environmental influences on trait variation
Partitioning of Phenotypic Values
We previously introduced the general model of Y = G +E where Y is the trait value, G is the genotypic value, and E is the environmental deviation that is assumed to have a mean of 0 so that E(Y ) = E(G). If we assume that the genetic and environmental components are independent, we have that the variance of Y is Var(Y ) = s 2 Y = s 2 G +s 2 E .
We previously focused on the decomposition of the genetic variance s 2 G into additive and dominance components, i.e., G = A+D

The amount of variation is measured and expressed as the variance. When values are expressed as deviations from the population mean the variance is simple the mean of the squared values. For example, the genotypic variance is the variance of genotypic values and the environmental variance is the variance of environmental deviations. The total variance is the phenotypic variance of the variance of phenotypic values, and is the sum of the separate components.
Components of Variance
The components of variance and the values whose variance they measure are listed as follows:
The total variance is the phenotypic variance, or the variance of phenotypic values, and is the sum of the separate components. Thus
But if genotypic values and environmental deviations are correlated, VP will be increased by twice the covariance of G with E because if P = G + E, VP = V (G + E) = VG + VE + 2 CovGE. d. The term 2 CovGE is zero when G and E are uncorrelated. Also when there is an interaction between genotypes and environments, there will be an additional component of variance due to the interaction i.e.

The concept of value, expressible in the metric units by which the character is measured. The value observed when the character is measured on an individual is the phenotypic value of that individual. All observations of means, variance, or covariances, must clearly be based on measurements of phenotypic values. In order to analyse the genetic properties of the population we have to divide the phenotypic value into two componants.
The first division of phenotypic value is into components attributable to the influence of genotypic and environment. The genotype is the particular assemblage of genes possessed by the individual, and the environment is all the non-genetic circumstances under the term ‘environment’ means that the genotype and the environment are by definition the only determinants of phenotypic value. The two components of value associated with genotypic value and the environmental deviation.
The mean environmental deviation in the population as a whole is taken to be zero. So that the mean phenotypic value is equal to the mean genotypic value. The term population mean than refers equally to phenotypic or to genotypic values. When dealing with successive generations we shall assume for simplicity that environment remains constant from generation to generation so that the population mean is constant in the absence of genetic change. If we replicate thea particular genotype in a number of individuals and measure them under environment conditions normal for the population, their mean environmental deviations would be zero and their mean phenotypic value would congiguently be equal to the genotypic value of that particular genotype.
In principle it is measurable, but in practice it is not, except when we are concerned with a single locus where the genotypes are phenotypically distinguishable or with the genotypes represented in highly inbred lines for example, considering a single locus with two alleles. A1 and A2, we call the genotypic value of one homozygote + a, that of the other homozygote – a and that of the heterozygote d (we shall adopt

Quantitative genetics is the study of continuous or quantitative traits and their underlying mechanisms. The main principals of quantitative genetics developed in the 20th century was largely in response to the rediscovery of Mendelian genetics. Mendelian genetics in 1900 centered attention on the inheritance of discrete characters, e.g., smooth vs. wrinkled peas, purple vs. white flowers. This focus was in stark contrast to the branch of genetic analysis by Sir Francis Galton in the 1870’s and 1880’s who focused on characteristics that were continuously variable and thus, not clearly separable into discrete classes. A contentious debate ensued between Mendelians and Biometricians regarding whether discrete characteristics have the same hereditary and evolutionary properties as continuously varying characteristics. I The Mendelians (led by William Bateson) believed that variation in discrete characters drove evolution through mutations with large effects I The Biometricians (led by Karl Pearson and W.F.R. Weldon) viewed evolution to be the result of natural selection acting on continuously distributed characteristics. This eventually led to a fusion of genetics and Charles Darwin’s theory of evolution by natural selection: main principals of quantitative genetics, developed independently by Ronald Fisher (1918) and Sewall Wright (1921), arguable the two most prominent evolutionary biologists.
Interestingly, Galton’s methodological approaches to continuously distributed traits marked the founding of the Biometrical school, which is what many consider to be the birth of modern statistics. Karl Pearson was inspired greatly by Galton, and he went on to develop a number of methods for the analysis of quantitative traits. We will talk more about Galton and Pearson later on in this course. One of the central goals of quantitative genetics is the quantification of the correspondence between phenotypic and genotypic values. It is well accepted that variation in quantitative traits can be attributable to many, possibly interacting, genes whose expression may be sensitive to the environment

A population, in the genetic sense, is not just a group of individuals, but a breeding group and the genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one generation to the next. In the transmission the genotypes of the parents are broken-down and a newest of genotypes is constituted in the progeny, from the genes transmitted in the gametes. The genes carried by the population thus have continuity from generation to generation, but the genotypes in which they appear do not. The genetic constitution of a population, referring to the genes it carries, is described by the array of gene frequencies, that is, by specification of the alleles present at every locus and the numbers of proportions of the different alleles at each locus. If for example, A1 is an allele at the A locus, then the frequency of A1, is the proportion or percentage of all genes at this locus that are the A1 allele. The frequencies of all the allele at any one locus must add up to unity, or 100 percent.
The gene frequencies at a particular locus among a group of individuals can be determined from knowledge of the genotype frequencies. To take a hypothetical suppose there are two alleles A1 and A2, let the frequencies of genes and of genotypes be as follows:

To understand how population genetics came into being, and to appreciate its intellectual significance, a brief excursion into the history of biology is necessary. Darwin’s Origin of Species, published in 1859, propounded two main theses: firstly, that modern species were descended from common ancestors, and secondly that the process of natural selection was the major mechanism of evolutionary change. The first thesis quickly won acceptance in the scientific community, but the second did not. Many people found it difficult to accept that natural selection could play the explanatory role required of it by Darwin’s theory. This situation— accepting that evolution had happened but doubting Darwin’s account of what had caused it to happen—persisted well into the twentieth century (Bowler 1988).
Opposition to natural selection was understandable, for Darwin’s theory, though compelling, contained a major lacuna: an account of the mechanism of inheritance. For evolution by natural selection to occur, it is necessary that parents should tend to resemble their offspring; otherwise, fitness-enhancing traits will have no tendency to spread through a population. In the Origin, Darwin rested his argument on the observed fact that offspring do tend to resemble their parents—‘the strong principle of inheritance’—while admitting that he did not know why this was. Darwin did later attempt an explicit theory of inheritance, based on hypothetical entities called ‘gemmules’, but it turned out to have no basis in fact.
Darwin was troubled by not having a proper understanding of the inheritance mechanism, for it left him unable to rebut a powerful objection to his theory. For a population to evolve by natural selection, the members of the population must vary—if all organisms are identical, no selection can occur. So for selection to gradually modify a population over a long period of time, in the manner suggested by Darwin, a continual supply of variation is needed. Fleeming Jenkin argued that the available variation would be used up too fast (Jenkin 1867). His reasoning assumed a ‘blending’ theory of inheritance, i.e., that an offspring’s phenotypic traits are a ‘blend’ of those of its parents. (So, for example, if a short and a tall organism mate, the height of the offspring will be intermediate between the two.) Jenkin argued that given blending inheritance, a sexually reproducing population will become phenotypically homogenous in just a few generations, far shorter than the number of generations needed for natural selection to produce complex adaptations.

1. Introduction
Molecular techniques are laboratory methods used to study and manipulate DNA, RNA, and proteins. These techniques are crucial for analyzing and understanding the molecular basis of biological processes and have applications in various fields like medicine, agriculture, and forensics.
2. Molecular Marker Analysis
Molecular markers can be expressed as a DNA sequence or gene expression product that represents differences in genomic level in relation to a gene or a property. Molecular markers are markers that can be used to monitor differences at the DNA level and for a gene that is being investigated. DNA markers are also DNA regions in which polymorphism in individuals within a species can be determined.
Molecular markers are nontissue-specific DNA regions that are reliable, repeatable, standardizable, capable of identifying multiple regions in the genome, capable of identifying more than one region in the genome, independent of environmental conditions, dominant and codominant.
Molecular markers are classified as dominant and codominant markers. Heterozygous individuals cannot be distinguished from homozygous dominant individuals, since dominant markers are not suitable for identification of heterozygous individuals when related to dominance between alleles is dominated by dominant markers. Thus, three different individuals (AA, AA and AA) can be distinguished for any marker at any point.
The use of molecular marker systems based on this meta-analysis has become more prevalent in genetic studies conducted by the discovery of the polymerase chain reaction (PCR). The rapid development of technology and the accompanying needs, the facilities of the laboratories where the applications will occur, the biological properties of the species and the abundance of markers in the genome have contributed to the development of DNA markers [5]. Restriction fragment length polymorphism (RFLP), randomly amplified polymorphic DNA markers (RAPD), amplified fragment length polymorphism (AFLP), sequence labeled sequences (STS), microsatellites (SSR), cleaved polymorphic sequence (CAPS), single strand such as complementary polymorphism (SSCP), amplicon length polymorphism (ALP), interspecific sequence repeat polymorphism (ISSR),

The genetic blueprint contained in the nucleotide sequence can determine the phenotype of an individual. The hereditary units, which are transmitted from one generation to the next generation are called genes. A gene is a fundamental biological unit like atom which is the fundamental physical unit.
Mendel was the first scientist who proposed genes as particulate units and called them hereditary elements or factors. But the concept of gene has undergone a considerable change since Mendel’s time.
Modern Concept of Gene
A gene can be described as a polynucleotide chain, which is a segment of DNA. It is a functional unit controlling a particular trait such as eye colour. Beadle and Tatum concluded by various experiments that gene is a segment of DNA that codes for one enzyme. They proposed one gene-one enzyme hypothesis. But as some genes code for proteins that are not enzymes, the definition of gene was changed to one gene-one protein hypothesis.
Protein Hypothesis
The concept of gene has undergone further changes as the new facts came to light. Since proteins are polypeptide chains of amino acids translated by mRNA, gene was defined as one gene-one polypeptide relationship.
Some proteins have two or more different kinds of polypeptide chains, each with a different amino acid sequence. They are products of different genes. For example, hemoglobin has two kinds of chains a andß chains, which differ in amino acid sequence and length. They are encoded by different genes. Thus, gene is defined as one gene- one polypeptide relationship.

DNA is the master molecule which carries the genetic information from one generation to the other. Study of Molecular Genetics accelerated since April 25th, 1953 when James Watson and Francis Crick proposed the structure of DNA which was published in Journal called ‘Nature’. Molecular Genetics deals with the flow of genetic information and its regulation. In simple terms it can be defined as the field of biology which studies the structure and function of genes at molecular level.
Scope of Molecular Genetics
Development of techniques like nucleic acid hybridisation, cloning, sequencing etc. brought a revolutionary change in Molecular Genetics. It is of major interest to the students of biology and medicine. Though it has a lot of significance in many fields, we’ll confine ourselves to the applications of molecular genetics to the mankind. They are as follows:
i) Diagnosis of infectious diseases: Normally microorganisms are detected in the laboratory using biochemical methods. In case of molecular techniques, microorganisms are detected by using probes (short DNA or RNA sequence) which are complementary to a part of genome of the microbe. The advantage of using molecular methods is:
• Identification of pathogen is done within a short time;
• No need to cultivate the microbes;
• Latent infections can also be identified when no antibody is formed; and
• The technique can be used even when the microorganism cannot be cultured.
ii) Diagnosis of genetic diseases : Before the advent of the above techniques, counselors used to give risk estimate like one fourth risk of getting the disease, if the parents are heterozygous for an autosomal trait. But now by directly testing for the mutation, they are able to confirm the presence or absence of mutation in the fetus. It is of immense help in prenatal diagnosis.

Introduction
• Cytogenetics is essentially a branch of genetics, but is also a part of cell biology/ cytology (a subdivision of human anatomy), that is concerned with how the chromosomes relate to cell behavior, particularly to their behaviour during mitosis and meiosis. Techniques used include karyotyping analysis of G-band chromosomes, as well as molecular cytogenetics such as fluorescent in situ hybridization (CGH). Cytogenetic approaches to studying chromosomes and their relationship to human disease have improved greatly over the past several decades.
As a mature enterprise, cytogenetics now inform genomics, disease and cancer genetics, chromosomes evolution and the relationship of nuclear structure to function. Cytogenetics involves testing samples of tissue, blood or bone marrow in a laboratory to look for changes in chromosomes including broken, missing, rearranged or extra chromosome. Cytogenetics may used to help diagnose a disease or condition, plan treatment or find out how well treatment is working.
Chromosomes
Chromosomes are the rod shaped; dark-stained bodies seen during metaphase stage of mitosis. The chromosomes are the nuclear components of special organization, individuality and function. They are capable of self-reproduction and play a vital role in heredity, mutation, variation and evolutionary development of the species. Chromosomes are thread-like structure located inside the nucleus. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. The number of chromosomes is constant for a particular species. Therefore, these are of great importance in the determination of the phylogeny and taxonomy of the species. The number of chromosomes varies from species to species but the number remains constant in a species. But sometime, due to certain accidents or irregularities at the time of cell division, crossing over or fertilization some alteration in morphology and number of chromosomes takes place. Humans have 23 pairs of chromosomes-22 pairs of numbered chromosomes, called autosomes, and one pair of sex chromosome, X and Y. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from mother and half from their father.