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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
Polled Dam
P
P
P
PP
PP
P
PP
PP
Punnett Square
N= Normal size
n= Dwarfism
Example:
• Normal size in cattle
is dominant to
dwarfism
Normal Dam
N
N
N
NN
NN
n
Nn
Nn
Punnett Square
N= Normal size
n= Dwarfism
Example:
• What if both parents
are carriers for a trait
or disorder?
Normal Dam
N
n
N
NN
Nn
n
Nn
nn
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
bp
bp
B P
B P
B bPp
B bPp
B bPp
B bPp
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)
Dihybrid Cross
BP
Bp
BP
Bp
bP
bp
BBPP
BBPp
BbPP
BbPp
BBpP
BBpp
BbPp
Bbpp
bbPp
bP
BbPP
BbPp
bbPP
bp
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
B P
B P
B B PP
B p
B B Pp
bP
B bPP
bp
B bPp
Dihybrid Cross
• If a (BbPp) bull is mated to a (BBPp) cow.
• what are the outcomes?
Dihybrid Cross
BP
BP
Bp
B BPP
B BPp
Bp
bP
bp
B BPp
B bPP
B bPp
B Bpp
B bPp
B bpp
Assignment
(Alternatives are horned and red)
Dam
Sire
Complete a Punnett
Square for two
animals that are
heterozygous for two
traits:
• Polled=P
• Black= B
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%
Trait
% Heritable
Number Born
5
Weaning Wight
30
Yeild Grade
30
Carcass Grade
35
Yearling Weight
40
Scrotal Circumference
50
Retail Yeild
60
Rib Eye Area
70
Trait
% Heritable
Litter Size
10
Weaning Wight (3 wks) 15
Birth Weight
20
Feed Efficiency
30
Carcass length
50
Trait
% Heritable
Number Born
13
Weaning Wight
30
Birth Weight
30
Feed Efficiency
20
Carcass (percent lean)
35

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