The Science of Animal Agriculture

Ch. 4

The Science of Genetics

Genetic Basics

• Gregor Mendel (1822-1884)– first person to develop workable theory

• transfer of traits

– used garden peas

– based on purebred strains

Law of Dominance

• overriding or dominant factors make certain recessive traits disappear

Law of Segregation

• the alleles responsible for the traits from each parent are separated and then combined with factors from the other parent at fertilization

Law of Independent Assortment

• Factors for certain characteristics are passed from parents to the next generation separate from the other factors or genes that transmit other traits

Punnett Square

• Developed by R.C. Punnett

• illustrates the possible combinations for a particular trait

RRR

R

rrrr

Rr

Rr

Rr

Rr

Punnett Square

• Developed by R.C. Punnett

• illustrates the possible combinations for a particular trait

RrR

r

RrrR

RR

Rr

Rr

rr

Genetics Basics

• genes are in chromosomes– different animals have different chromosome

#’s• cattle = 30 pairs• horses = 32 pairs• apples = 34 pairs

• each allele contains two genes– one by each parent

Selective Breeding

• the choosing of individuals of a single strain and species

• artificial selection

• need to avoid inbreeding

Hybridization

• the crossing of different species

• hybrid vigor– the ability of hybrids or strain crosses to

exceed the parents in performance

• most hybrids are sterile

Crossbreeding

• the mating of unrelated strains of the same species to avoid inbreeding