Topic 3033 Animal Genetics Genotype and Phenotype Anna Blight

Genetic Terminology DNA to RNA to protein Protein codes for genes Genes code for traits Each chromosome pair contains many gene pairs

Alleles genes that occupy specific loci on chromosomes and affect the same trait There are TWO alleles, one on each chromosome of the homologous pair If loci correspond the animal is homozygous (AA, aa), if the alleles contrast the animal is heterozygous (Aa) Coat color is determined by dominance of one of the alleles (Aa) or homozygosity of recessive alleles (aa)

Genetic Terminology For example, during gametogenesis a heterozygous animal passes a white allele to one gamete and the black allele to the other gamete Resulting germ cells pass on either a white allele or a black allele, not both because of segregation of the homologous chromosomes Homozygous animals pass on two of the same alleles to gametes

X and Y Chromosomes Determine sex of the animal Females = XX (except bird eggs = XY) Males = XY (bird species sperm = XX) Females only contribute X to gametes Males contribute both X and Y thus determining sex of animal Reversed in bird species

Pairs of Chromosomes in Livestock and Poultry Turkeys Chickens Horses Cattle Goats Sheep Humans*(comparison) Swine

Genotype and Phenotype Genotype Genetic constitution of an individual For any pair of alleles, three genotypes are possible AA Aa aa Phenotype Characteristics of an animal that can be seen Example: presence or absence of horns, color, or weight Determined by genotype

Dominant Expression Dominant gene overpowers expression of its recessive allele Represented by a capital letter Example: a black holstein is dominant over red coat color

Dominance Homozygous dominant, WW W = White Heterozygous sheep Ww, w = black Sheep will show dominant trait and be white

Recessive Expressions Black wool Recessive trait for sheep Homozygous recessive ww Both parents must carry recessive allele

Common Known Dominant and Recessive Traits in Livestock Dominant Polled cattle Black Holstein or Angus Belted Pattern in swine Trotting Gait Black horse Recessive Horned cattle Red Holstein or Angus Non-Belted Pattern- swine Pacing Gait Chestnut horse

Genotypic & Phenotypic Ratios Using the Punnett Square Heterozygous mated with homozygous dominant 1:1 genotypic ratio 50% homozygous, 50% heterozygous. All offspring look the same. WW WW WW wWw

Genotypic & Phenotypic Ratios Using the Punnett Square Mating two heterozygous sheep Genotypic ratio of 1:2:1 Phenotypic ratio is 3:1; three white sheep, one black sheep Punnett square is an easy way to determine ratios Ww WWWWw w ww

Multiple Gene Pairs Two traits, Red or black coat color and polled or horned cattle Gives nine genotypes Four phenotypes, 9:3:3:1 ratio 9 Black polled, 3 black horned, 3 red polled, and 1 red horned

Multiple Gene Pairs B=black coat b=red coat P=polled p=horned cattle BPBpbPbp BPBBPPBBPpBbPPBbPp BpBBPpBBppBbPpBbpp bPBbPPBbPpbbPPbbPp bpBbPpBbppbbPpbbpp

How would understanding genotype and phenotype, and dominant and recessive traits contribute to a breeding program?

Bibliography Taylor, Robert E., Field, Thomas G Scientific Farm Animal Production: An Introduction to Animal Science. Upper Saddle River: Prentice Hall.