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 ID: 194878
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Slide1
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 Slide2
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 letterSlide3
Genes
Example:
The dominant gene is written-
P
The recessive gene is written-
p
P
= Polled
p
= hornedSlide4
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 PpSlide5
Punnett Square
P
= Polled
p
= horned
Example:
Two polled cattle that are homozygous for the polled trait
P
P
P
PPPPPPPPP
Polled Dam
Polled SireSlide6
Punnett Square
N= Normal size
n= Dwarfism
Example:
Normal size in cattle is dominant to dwarfism
N
N
N
NN
NN
nNnNn
Normal Dam
Sire CarrierSlide7
Punnett Square
N= Normal size
n= Dwarfism
Example:
What if both parents are carriers for a trait or disorder?
N
n
N
NN
Nn
nNnnn
Normal Dam
Sire Carrier
Result
: one out of every four births could result in a dwarf animal (1:2:1)Slide8
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
?Slide9
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).Slide10
Dihybrid Cross
Black = 100%
Polled = 100%
Horned = 0%Slide11
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)Slide12
Dihybrid CrossSlide13
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%Slide14
Dihybrid Cross
If a heterozygous bull (BbPp) is mated to a homozygous cow (BBPP).
What are the outcomes?Slide15
Dihybrid CrossSlide16
Dihybrid Cross
If a (BbPp) bull is mated to a (BBPp) cow.
what are the outcomes?Slide17
Dihybrid CrossSlide18
Assignment
Complete a Punnett Square for two animals that are heterozygous for two traits:
Polled=P
Black= B
(Alternatives are horned and red)
Dam
SireSlide19
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
".Slide20
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. Slide21
Heritability
Objective:
Discuss hertability estimates for beef and swineSlide22
Heritability
Estimated the likelihood of a trait being passes on from the parent to the offspring
Low heritability
slow herd improvement
High heritability
faster improvementSlide23
Heritability
Swine rates are usually lower than cattle
Heritiability for carcass traits are higher than reproductive traits
Estimates vary from 0 to 70%Slide24
Heritability
Estimates - cattle
Trait % Heritable
Number Born 5
Weaning Wight 30
Yeild
Grade 30
Carcass Grade 35
Yearling Weight 40
Scrotal Circumference 50
Retail Yeild 60Rib Eye Area 70Slide25
Heritability
Estimates - Swine
Trait % Heritable
Litter Size 10
Weaning Wight (3
wks
) 15
Birth Weight 20
Feed Efficiency 30
Carcass length 50Slide26
Heritability
Estimates - Sheep
Trait % Heritable
Number Born 13
Weaning Wight 30
Birth Weight 30
Feed Efficiency 20
Carcass (percent lean) 35