Animal Genetics

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General features and mechanisms

• Cell differentiation
• Body plan
• Methods
• Signaling

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4 processes important for multicellular development

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Basic animal body plan with ectoderm, mesoderm, & endoderm

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Regulatory DNA can provide differences even if gene products are similar

Mice

• embryogenesis
• Stem cell manipulation

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Mice - model for mammalian development - early stages

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Cells from early developmental stages can be combined to create chimeric mice

Major Factors Influencing Genetic Change

​

​

Genetic

Change=

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Accuracy

of

Selection

X

Selection

Intensity

X

Genetic Variation

Generation Interval

Selection Intensity

• Is dependent up the proportion of animals kept as parents for the next generation.
• Intensity also includes the superiority of those animals compared to the genetic average of the overall population.

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Generation Interval

• Is the average age of a parent when the offspring is born.

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Phenotype

• The Phenotype of the cow is what you observe or measure.
• 305-day record
• Classification score
• Ex: White feathers

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Genotype

• Genotype is the actual genes that the animal possesses for a given trait.
• Ex: AA, Aa, aa

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Qualitative Traits

• Qualitative traits are generally controlled by one pair of genes which generally result in the same phenotype.
• Examples

Sex

Hair coat

Horns

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Quantitative Traits

• Quantitative traits are controlled by many genes, with each gene generally having a relatively small influence on the expression of a trait.
• Examples

Milk production

Fat percentage

Final score

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Breeding Value

• Breeding value is defined as the total genetic ability of an animal for a given trait. An individual receives one-half of their breeding value from each parent.

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Breeding Value=

Sire’s Transmitting Ability

+

Dam’s Transmitting Ability

Transmitting Ability

• Transmitting ability is an estimate of the average genetic merit that will be passed from parent to offspring

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Transmitting Ability= ½ Breeding Value

Selection Intensity

• Selection intensity measures the relative superiority of the group of animals allowed to reproduce.
• The selection intensity in bulls is high because only a small number are needed to produce adequate amounts of semen for the U.S. dairy cow population.

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What is Selection?

• Mating animals to produce certain characteristics
• Low Birthweight
• Heavier Weaning Weight
• Color
• Horned or Polled
• Temperment

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Genetics

• All body cells contain “Blueprints” with instructions as to how an animal will look or act etc.
• One Gene comes from each parent (pairs)
• Genes are divided into sections (Chromosomes) that carry genes
• Sex chromosomes: male = XY, female = XX

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Dominant Genes

• Examples of Dominant Genes
• Dominant Genes = one gene overshadows the other
• Angus Cattle: black is dominant, red is not (Bb)
• Hereford: white face is dominant (Ww)
• Polled is dominant over horned (Pp)

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Recessive Genes

• The gene that is overshadowed by a dominant gene
• Recessive genes can only express themselves if both genes are recessive
• Polled vs Horned (Pp) (pp)
• Black wool vs white (Ww) (ww)

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Punnet Square

• P = Polled
• p = horned
• If a homozygous horned cow (pp) is mated to a homozygous polled bull (PP), what percent of the calves will be horned, polled?

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Punnet Square

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Punnet Square

• If a homozygous horned cow (pp) is mated to a heterozygous polled bull (Pp), what percent of the calves will be polled?

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Punnet Square

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Sex Linked Genes

• Some recessive genes are attached to the X and Y chromosomes
• Humans: Colorblindness and Baldness are on the X chromosomes
• In Men, traits expressed anytime present
• In Women, must have two recessives to show trait
• Children get baldness from mothers

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Punnet Square: What sex will the offspring be?

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If Dad is bald, will you be bald?

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Baldness is carried by the mother

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What if Mom is bald?

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Incomplete Dominance?

• If both genes express themselves
• Shorthorn Cattle: Red male mated to a White female = Roan calf
• RR + WW = RW

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Punnet Square

• Shorthorn Cattle
• R = Red
• W = white
• RW = roan
• If a red bull (RR) is mated to a white cow (WW), what color will the calves be?

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Shorthorn: Red X White

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Punnet Square

• If a red bull (RR) is mated to a roan (RW) cow, what color will the calves be?

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Shorthorn: Red X Roan

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What if Both Parents are Roan?

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Undesirable Characteristics

• Dwarfism
• Monorchid = only one testicle descends
• Cryptorchid = no testicles descend
• Short ears & tails

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Mutation

• Dramatically different from what is expected genetically
• Horned calf from polled parents
• Loss of some or extra body parts
• Lethal Mutation: causes death at birth
• Sublethal Mutation: limits animals ability to grow to maturity
• Beneficial Mutation: loss of tail in lambs

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What is an Abnormality?

• Similar to a Mutation, only it is caused by something in the environment
• Siamese twins

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What is Heritability?

• Chance that traits will be inherited
• Low: multiple births, fat covering
• Medium: birth wt, wean wt, milk, wool grade, carcass wt, rate of gain
• High: Loin eye area, fleece length & quality

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Heritability

• Currently have ewes that wean 70 lb lambs
• Want to raise weaning wt to 110 lbs
• Select a ram with a wean wt of 110 lbs
• Heritability of weaning wt is 30%
• What can you expect new lamb crop to weigh at weaning?

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Heritability

• What is the difference in current weaning wt and that of the new ram?

110 - 70 = 40 lbs

• Heritability % x difference

30% x 40 = 12 lbs

• Can expect a gain in weaning wt of 12 lbs
• 70 lbs + 12 lbs = 82 lbs

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Mating Systems

• Random Mating: all males have an equal opportunity to mate with all females
• Outcrossing: mating purebreds with unrelated purebreds
• Inbreeding: mating related animals
• Linebreeding: parents mated to offspring
• Crossbreeding: mating animals of same species but different breeds

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Hybrid Vigor

• Offspring will outperform either of the parents
• Corn Breed A yields 100 bu/acre
• Corn Breed B yields 100 bu/acre
• Crossbreed A & B yields corn that yields 200 bu/acre
• Vigor only expressed in crossbreeding
• Donkey mated to a horse = Mule
• mule is sterile

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Genetic Terms

• Genotype: genetic makeup (Bb)
• Phenotype: physical appearance (Black)
• Heterosis: Genes are different, Dominant & Recessive (Bb)
• Homozygous: both genes are the same (BB or bb)

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