Basic Mendelian genetics applied to livestock Asst Prof

Basic Mendelian genetics applied to livestock Asst. Prof. Dr. Wuttigrai Boonkum Department of Animal Science Khon Kaen University

What is genetics ? • “Genetics is the study of heredity, the process in which parents pass certain genes onto their offspring. ” • Offspring inherit their biological parents’ genes that express specific traits, such as some physical characteristics, natural talents, and genetic disorders.

What is genetics ? Watson and Crick (found in April, 1953)

Genetic concepts • Heredity describes how some traits are passed from parents to their offspring. • The traits are expressed by genes, which are small sections of DNA that are coded for specific traits. • Genes are found on chromosomes. • Humans have two sets of 23 chromosomes— one set from each parent.

Mendelian Inheritance • The inherited traits are determined by genes that are passed from parents to offspring. • A offspring inherits two sets of genes one from each parent. • A trait may not be observable, but its gene can be passed to the next generation.

Example number of chromosome in animal Common name Human Horse Ass European cattle Zebu cattle American bison Domestic buffalo River buffalo Musk Ox Reindeer Sheep Goat Swine Dog Cat Rabbit Mouse Rat Chicken Scientific name Homo sapiens Equus caballus Equus asinus Bos tausus Bos indicus Bison bison Bubalus bubalis Ovibos moschatus Rangifer tarandus Ovis aries Capra hircus Sus scrofa Canis familiaris Felis catus Oryctolagus cuniculus Mus musculus Rattus norvegicus Gallus gallus Chromosome number 46 64 62 60 60 60 48 52 48 70 54 60 38 78 38 44 40 42 70 -80

Classical (Mendelian) Genetics • • Principles of genetics were developed in the mid 19 th century by Gregor Mendel an Austrian Monk Developed these principles without ANY scientific equipment - only his mind. Experimented with pea plants, by crossing various strains and observing the characteristics of their offspring. Studied the following characteristics: – – • • • Pea color (Green, yellow) Pea shape (round, wrinkled) Flower color (purple, white) Plant height (tall, short) Made the following observations (example given is pea shape) When he crossed a round pea and wrinkled pea, the offspring (F 1 gen. ) always had round peas. When he crossed these F 1 plants, however, he would get offspring which produced round and wrinkled peas in a 3: 1 ratio.

Laws of Inheritance • Law of Segregation: When gametes (sperm egg etc…) are formed each gamete will receive one allele or the other. • Law of independent assortment: Two or more alleles will separate independently of each other when gametes are formed

Law of segregation Segregation of genes Recombination of genes Inter se mating

Six basic genotype crosses เมอผสมพนธสตวทม genotype homozygous x homozygous ไดลกทม แบบเดยว homozygous x heterozygous ไดลกทม 2แบบ ½ : ½ heterozygous x heterozygous ไดลกทม ครบทกแบบ genotype parents progeny 1 AA x AA all AA 2 AA x aa all Aa 3 aa x aa all aa 4 Aa x AA 1/2 Aa, 1/2 AA 5 Aa x aa 1/2 Aa, 1/2 aa 6 Aa x Aa 1/4 AA, 1/2 Aa, 1/4 aa