INTRODUCTION TO ANIMAL GENETICS &

HISTORY OF GENETICSDR. ASHISH PATEL

Assistant professorDept. AGB, AAU, Anand

Title of important books:

Principles of Genetics by Gardner, Simmions and Snustad. Fundamental of Genetics by B.D.Singh A Textbook of Animal Genetics by P.Kanakraj Introduction to Veterinary Genetics by F.W.Nicholas Animal Genetics: concept and implication by Gurvinder

Singh The Genetics of Populations by J.L.Lush Introduction to Quantitative Genetics by D.S. Falconer

History of Genetics

Gregor Mendel the “Father of Genetics"

Year Scientist(s)

Discovery

1666 Hooke Discovery of cells.

1831 Brown Discovery of nucleus as a central feature of cells.

1858 Charles Darwin

The theory of evolution through natural selection.

1859 Charles Darwin

Published The Origin of Species.

1866 Gregor Mendel

Published the results of inheritance of "factors" in pea plants.

Year Scientist(s) Discovery

1900 Carl Correns, Hugo de Vries andErich von Tschermak

Rediscovered Mendel's principles independently.

1903 Johannsen, W.L.

coined the terms phenotype andgenotype

1903 Walter Sutton and Boveri

Chromosomal theory of inheritance.

1905 William Bateson

Coined the term "genetics“.

1905 Nettie Stevens Edmund Wilson

Independently described the behavior of sex chromosomes -XX determines female; XY determines male.

Year Scientist(s)

Discovery

1908 Correns, Bateson and Punnet

Discovery of gene linkage.

1910 T. H. Morgan Proposed a theory of sex-linked inheritance, followed by the gene theory, including the principle of linkage.

1913 Alfred Sturtevant

Made the first genetic map of aChromosome.

1913, 1916

Bridges Non-disjunction as a proof of chromosome theory of inheritance.

1927 H. J. Muller Used x-rays to cause artificial gene mutations in Drosophila.

1928 Frederick Griffith

Discovered that hereditary material from dead bacteria can be incorporated into live bacteria.

Year Scientist(s) Discovery1933 Jean Brachet Showed that DNA is found in

chromosomes and that RNA is present in the cytoplasm of all cells.

1936 Stern Discovery of mitotic crossing over.

1941 Edward Lawrie Tatum and George Wells Beadle

Showed that genes code forProteins.

1950 Erwin Chargaff

Discovered a one-to-one ratio of adenine to thymine and guanine to cytosine in DNA samples.

Year Scientist(s) Discovery

1953 James Watson and Francis crick

Double helix structure of DNA.

1953 F.H.C. Crick and J.D. Watson

Solved the three-dimensional structure of the DNA molecule.

1958 Meselson-Stahl

Semi-conservative replication of DNA.

1958 Matthew Meselson Frank Stahl

Used isotopes of nitrogen to provethe semi-conservative replication ofDNA.

Year Scientist(s) Discovery

1970 Hamilton Smith & Kent Wilcox

Isolated the first restriction enzyme – Hind II.

1972 Paul Berg Herb Boyer

Produced the first recombinant DNA molecules.

1983 Kary B. Mullis Polymerase chain reaction.

1989 Alec Jeffreys Coined the term DNA fingerprinting andwas the first to use DNA polymorphismsin paternity, immigration, and murder cases.

Scientist Discovery

Har Govind Khurana

Indian-American molecular biologist. He was awarded the Nobel Prize (shared with Robert W. Holley and Marshall Warren Nirenberg) in 1968 for his work on the interpretation of the “genetic code and its function in protein synthesis”.

Genetics

Derived from the Greek word gene, which means to become or to grow.

Since characters are governed by genes, genetics is the study of structure, composition and function of genes.

Genetics is a science which deals with the principles of heredity and variation. It studies the inheritance of various characters from one generation to another.

Heredity includes those traits or characteristics which are transmitted from generation to generation and is, therefore, fixed for a particular individual.

Variations are mainly of two types:

(i) hereditary, and

(ii) environmental

Hereditary variations refer to differences in inherited traits. Such variations are found in progenies of different parents as well as among progeny from the same parents. Hereditary variations are transmitted from generation to generation.

Environmental variations are those which are just due to environment. Environmental variations are temporary and have nothing to do with the previous or the next generation.

Branches of genetics

Animal Genetics - It deals with inheritance of traits in animals.

Plant Genetics - It deals with inheritance of characters in various plant species.

Microbial Genetics - It deals with inheritance of traits in microorganisms like bacteria, viruses and fungi.

Molecular Genetics - It deals with the structure, composition, function and replication of genes.

Population Genetics - It deals with frequencies of genes and genotypes in a population as well as with various factors which tend to alter gene frequencies in a population leading to evolutionary changes.

Cytogenetics - It deals with combined study of cytology and genetics. That means study of chromosome.

Euphenics - It deals with the control of hereditary diseases especially inborn errors of metabolism.

Radiation Genetics - It deals with effects of various types of radiations on chromosomes and genes.

Eugenics - It deals with the application of genetic principles for the better ment of human race.

Mendelian Genetics - It deals with the inheritance of qualitative characters or oligogenic characters which display discontinuous variation.

Quantitative Genetics - It deals with the inheritance of polygenic or quantitative characters. This branch of genetics is also known as biometrical genetics or statistical genetics or mathematical genetics.

Pre-Mendelian Concepts about Heredity

(1) Preformation Theory (Swammerdam and Bonnet )

This theory states that a miniature human called humanculus was already present in the egg and sperm. In other words, a miniature human was preformed in the gametes. The development of zygote resulted only in the growth of miniature human who was already present in the egg and sperm.

This theory was not acceptable because this could not be proved scientifically.

(2) Theory of Epigenesis (Wolff)This theory states that egg or sperm cells do not contain miniature human. In other words, egg or sperm cells are undifferentiated. The differentiation into various organs or parts takes place only after fertilization from the zygote resulting into development of adult tissues and organs.

This concept is known as epigenesis which is universally accepted.

(3) Theory of Acquired Characters (Lamarck )

This theory states that a new character once acquired by an individual shall pass on to its progeny.

This theory was disproved by Weismann. He cut the tail of mice for 22 successive generations and always got the baby mice with tail.

Thus, this theory was soon rejected.

(4) Theory of Pangenes (Charles Darwin )

This theory states that very small, exact but invisible copies of each body organ and component (called gemmules) are transported by the blood stream to the sex organs.

These gemmules are assembled in the gametes. After fertilization these gemules move out to different parts of the body resulting in the development of respective organ.

This theory was also rejected because it did not have scientific basis.

(5) Germplasm Theory

This theory states that body tissues are of two types, viz., germplasm and somatoplasm.

The germplasm refers to the reproductive tissues or cells which produce gametes. The somatoplasm includes all other body tissues which are not related to sexual reproduction.

Thus, transmission of characters from one generation to other takes place only through germplasm. Any change in the germplasm will lead to change in the next generation.

This theory is accepted in a broad sense.

Applications of Genetics

Genetics has important practical applications in the various fields:

(1) Taxonomy - It helps in classification of animals / plants/ organisms based on chromosome number

(2) Veterinary - It helps in the improvement of domestic animals. The milk production in cows and buffaloes, meat production in sheeps, goats and pigs and egg production capacity in poulty have been significantly improved through the application of genetic principles.

Similarly, many improved breeds of pet animals like horse, dogs, cats, pigeon and rabbits have been developed all over the world.

(3) Medicine –

(i) Detection of Hereditary Diseases - Hereditary diseases can be detected at an early stage of life. Moreover, genetic diseases can be prevented by advising future parents with the help of family pedigrees.

(ii) Production of Antibioties - Special genetic strains of fungi and bacteria have been isolated to greatly increase the yields of antibiotics and other drugs.

(4) Evolution – Through both natural and artificial selections.