Genetics

Animals are …

diploid

• two copies of genetic material, one from each parent

chromosomes

DNA organized into long, unbroken strands

gene

functional units within chromosomes

the position of gene on chromosomes is called

locus

genes usually have 2 alternate forms called ______

alleles

homozygous

two alleles for a particular gene are identical (BB,bb)

heterozygous

two alleles for a particular gene are different (Bb)

dominance

simple dominance

• ex: BB,Bb- black, bb- red

incomplete dominance

• heterozygote is intermediate of the two homozygotes

• R- “dominant”

• r- “recessive”

codominance

• heterozygote expresses both alleles

• ex: shorthorn cattle coat color

• often denoted by X,X’

Overdominance

• heterozygote is superior to either homozygote

• usually associated with fitness or survivability

• often what we get with heterosis

Epistasis

interaction of non-allelic genes

• ex: coat color of labs

• E/e gene influences B/b gene even though they are not alleles

autosomes

all chromosomes but the sex chromosomes

mammal sex chromosomes

XX= female

XY= male

bird sex chromosomes

ZZ= female

ZW= male

sex-linked inheritance

X-chromosomes

• larger and longer than Y

• male-portion of X that does not pair with Y

• these genes are sex-linked

usually recessive

red-green color blindness, hemophilia

orange color in cats

sex-limited traits

• genes transmitted by both sexes (influenced by both chromosomes), but only expressed in one sex

• ex: lactation, egg-laying

trait

observable or measurable characteristic

• height

• eye color

• hair color

phenotypes

observed category or level of performance

• 5 ft 4in

• blue

• blonde

types of traits

how many genes affect the trait?

• a few

  • monogenic (Mendel)

• Many

  • polygenetic (animal breeding)

polygenic traits

how is trait evaluated?

• defined categories

  • qualitative

• continuous spectrum

  • quantitative

qualitative traits

• coat color

• udder score, vulva score, foot and leg score

• puppies, kittens per litter

quantitative traits

• continuous spectrum

• objectively measured

• carcass quality, weight related measures, muscle ultrasound, running speed, etc

Phenotypes

observed category or level of performance

• what you see

• Genotype + environment

genotype

the genes an animal possesses (DNA)

heritability

degree of phenotypic variation that is due to genetics

• Lower= less responsive to selective breeding and slower genetic process

genetic improvement

goal of breeding is to improve populations, not individuals

breeding value (BV)

value of that animal as a parent

expected progeny difference (EPD)

the difference in performance from the expected progeny of a sire compared to the performance of progeny of an average sire

inbreeding

mate related animals

• increased homozygosity, uniformity

• reduced performance and survivability

linebreeding

form of inbreeding

• maximize relationship to a superior ancestor

• minimize inbreeding

• swine, poultry, horses

crossbreeding

less related individuals mated

• often different breeds

• increased heterozygosity, performance

heterosis

hybrid vigor, superiority of crossbred relative to average of parent breeds

complementarity

mating breeds that excel at different traits to match strengths and weaknesses