Presentation on theme: "Genes Located on chromosomes Thousands found in each animal Control inherited characteristics – Carcass traits – Growth rate – Feed efficiency Two types."— Presentation transcript:
Genes Located on chromosomes Thousands found in each animal Control inherited characteristics – Carcass traits – Growth rate – Feed efficiency Two types of inherited traits Dominant Recessive
Genes 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
Genes Example: The dominant gene is written- P The recessive gene is written-p P= Polled p= 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= Polled p= horned Example: Two polled cattle that are homozygous for the polled trait PP PPP P Polled Dam Polled Sire
Punnett Square N= Normal size n= Dwarfism Example: Normal size in cattle is dominant to dwarfism NN NNN nNn Normal Dam Sire Carrier
Punnett Square N= Normal size n= Dwarfism Example: What if both parents are carriers for a trait or disorder? Nn NNNNn n nn Normal Dam Sire Carrier Result: 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 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)
Assignment Complete a Punnett Square for two animals that are heterozygous for two traits: Polled=P Black= B (Alternatives are horned and red) Dam Sire
Practice Black 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%