Genes

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• Located on chromosomes• Thousands found in each animal• Control inherited characteristics– Carcass traits– Growth rate– Feed efficiency

• Two types of inherited traits Dominant Recessive

• Dominant gene– Hides the effect of another gene– Polled condition in cattle is dominant– The gene is represented by a capital letter

• Recessive– Gene that is hidden by another– The gene is represented by a lower case letter

Example:

The dominant gene is written- P

The recessive gene is written-p

P= Polledp= horned

Homozygous and Heterozygous

• Homozygous gene pair– Carries two genes for a trait– Polled cow might carry the gene PP

• Heterozygous (or hybrid)– Carries two different genes that affect a trait– Polled cows might carry a recessive gene with the

dominant Pp

Punnett Square

P= Polledp= hornedExample:• Two polled cattle that

are homozygous for the polled trait

P PP PP

Polled Dam

Punnett Square

N= Normal sizen= DwarfismExample:• Normal size in cattle

is dominant to dwarfism

N NN NN

n Nn Nn

Normal Dam

Punnett Square

N= Normal sizen= DwarfismExample:• What if both parents

are carriers for a trait or disorder?

N NN Nn

n Nn nn

Normal Dam

erResult: one out of every four births could result in a dwarf animal (1:2:1)

Monohybrid Cross

• A monohybrid cross is an estimation of a predicted outcome for a single trait.

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

Dihybrid Cross • A dihybrid cross is a estimation of a predicted

outcome for two traits.• What results if an Angus bull that is homozygous

black and polled (BBPP) is bred with a red shorthorn cow which is homozygous red and horned (bbpp).

• The bull BBPP can be simplified to BP (black & polled is the only possible contribution for the bull).

• The cow bbpp can be simplified to bp (red & horned is the only possible contribution for the cow).

Dihybrid Cross

BbPp BbPp

Black = 100%Polled = 100%Horned = 0%

Dihybrid Cross

• Now if two of the offspring which are heterozygous for black/red and polled/horned (BbPp) are mated.

• How do you do a Punnett square for two heterozyous animals?

• Use all possible gene combinations.• Both the bull and cow are BbPp.• What are the possible contributions?• BP, Bp, bP, bp for both animals. (4 x 4 grid)

BP Bp bP bp

BBPP BBPp BbPP BbPp

BBpP BBpp BbPp Bbpp

BbPP BbPp bbPP bbPp

BbPp Bbpp bbPp bbpp

Dihybrid Cross

• Black Polled = 9 out of 16 or 56.25%• Black Horned = 3 out of 16 or 18.75%• Red Polled = 3 out of 16 or 18.75%• Red Horned = 1 out of 16 or 6.25%

Dihybrid Cross

• If a heterozygous bull (BbPp) is mated to a homozygous cow (BBPP).

• What are the outcomes?

Dihybrid Cross

BP Bp bP bp

BP BBPP BBPp BbPP BbPp

Dihybrid Cross

• If a (BbPp) bull is mated to a (BBPp) cow.• what are the outcomes?

Dihybrid Cross

BP Bp bP bp

BBPP BBPp BbPP BbPp

BBPp BBpp BbPp Bbpp

Assignment

Complete a Punnett Square for two animals that are heterozygous for two traits:

• Polled=P• Black= B

(Alternatives are horned and red)

PracticeBlack is dominant (B), and red is recessive (b). "Predict the offspring from the cross of a red bull and a black cow if the black cow's mother was red".

First things first: the only way for the red bull to be red (the recessive trait) is if it's genotype is homozygous recessive (2 little letters), so the red bull is "bb". Now, the black cow's genotype could be either "BB" or "Bb". If its mommy was red (bb), then this black cow MUST have inherited a little "b" from its mommy. So the black one in our cross is "Bb" (not "BB"), and our cattle cross is: Bb x bb.

Heritability

• Objective:– Discuss hertability estimates for beef and swine

Heritability

• Estimated the likelihood of a trait being passes on from the parent to the offspring– Low heritability• slow herd improvement

– High heritability• faster improvement

Heritability

• Swine rates are usually lower than cattle• Heritiability for carcass traits are higher than

reproductive traits• Estimates vary from 0 to 70%

Trait % HeritableNumber Born 5Weaning Wight 30Yeild Grade 30Carcass Grade 35Yearling Weight 40Scrotal Circumference 50Retail Yeild 60Rib Eye Area 70

Trait % HeritableLitter Size 10Weaning Wight (3 wks) 15Birth Weight 20Feed Efficiency 30Carcass length 50

Trait % HeritableNumber Born 13Weaning Wight 30Birth Weight 30Feed Efficiency 20Carcass (percent lean) 35

Genes

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