Download Inheritence of Quantitative Traits

Gene350 Animal Genetics
Lecture 15
31 August 2009
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Single genes in Animal Breeding
– Examples and uses
Today
•
Inheritance of Quantitative traits in animals
–
–
Heritability
Repeatability
Inheritance of Quantitative Traits
Quantitative traits
can be measured
genetically determined by
many gene pairs
.
Inheritance of Quantitative Traits
P=G+E
Phenotype = Genotype + Environment
P=A+D+I+E
P = additive + dominance + epistasis + E .
Inheritance of Quantitative Traits
Genotype
AA
Aa
aa
Additive
Value
+4
+2
+0
.
Inheritance of Quantitative Traits
Genotype
BB
Bb
bb
Value
+4
+4
+0
Complete Dominance .
Inheritance of Quantitative Traits
Genotype
CC
Cc
cc
Value
+4
+3
+0
Partial dominance
.
Inheritance of Quantitative Traits
Genotype
DD
Dd
dd
Value
+4
+6
+0
Overdominance
.
Inheritance of Quantitative Traits
P = A + D + I + Ep +Et
Ep = permanent environment
Et = temporary environment .
Inheritance of Quantitative Traits
Permanent environment
environmental effect on all
subsequent records
Temporary environment
environmental effect on
current record
P = A + D + I + Ep +Et
.
Inheritance of Quantitative Traits
Permanent environmental effects
severe illness
failure to have a calf one year
injury to udder
frostbite
Temporary environmental effect
heat wave
slight illness
off feed
.
Variation in a herd
Vp = Vg + Ve
phenotypic variance
genetic variance
environmental variance
.
Variation in a herd
Vp = Va + Vd + Vi + Vep + Vet
additive variance
dominance variance
epistatic variance
permanent environmental variance
temporary environmental variance .
M
or
e
60
0
55
0
50
0
45
0
40
0
35
0
Frequency
Weaning Weight
100
80
60
40
20
0
Variation in a herd
normal distribution of phenotypes
underlying normal distributions of
additive effects
dominance effects
epistatic effects
perm env effects
temp env effects
.
Variation in a herd
best animals may have
best additive genotype
best dominance genotype
best epistatic genotype
best perm env
best temp env
and/or best combination of
these effects
.
M
or
e
60
0
55
0
50
0
45
0
40
0
35
0
Frequency
Weaning Weight
100
80
60
40
20
0
heritability
VA =
VA
h 
VP
V A  VD  VI  VEP  VET
2
define - proportion of phenotypic
variation that is due to
additive gene effects
most important concept in
Animal Genetics
.
Heritability
traits
reproductive
growth
carcass
h2 magnitude
<.2 low
.2-.4 moderate
.4-.6 high
few traits have
2
h
> .6
proportion of phenotypic variation that is due
to additive gene effects=
beef cattle
birth weight
weaning weight
weaning score
feedlot gain
carcass grade
fat thickness
rib eye area
marbling
retail product %
calving interval
conception rate
h2
.35
.30
.25
.45
.40
.33
.58
.42
.30
.08
.05
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Dairy cattle
milk yield
fat yield
solids-not-fat yield
protein yield
fat %
solids-not-fat %
protein %
type score
h2
.25
.25
.25
.25
.50
.50
.50
.30
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Swine
ovulation rate
litter size
survival to weaning
21-day litter wt
average daily gain
days to 230 pounds
backfat thickness
feed efficiency
loin eye area
carcass length
h2
.39
.10
.05
.15
.30
.25
.41
.30
.47
.56
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Sheep
90-day weight
postweaning gain
grease fleece wt
fiber diameter
staple length
fat thickness
loin eye area
ewe fertility
prolificacy
lamb survival
carcass weight
dressing %
h2
.25
.40
.35
.40
.55
.30
.50
.05
.10
.05
.35
.10
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Horse
pulling ability
cutting ability
Thoroughbred
earnings
handicap wt
Trotter
earnings
time
wither height
heart girth
services / conceptions
h2
.25
.04
.09
.33
.20
.32
.43
.29
.12
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Layers
chick livability
adult livability
body depth
adult body weight
egg production
egg weight
fertility
Broilers
7-week weight
feed consumption
feed conversion
breast fleshing
fat deposition
h2
.05
.10
.25
.55
.15
.55
.05
.45
.70
.35
.10
.50
proportion of
phenotypic
variation
that is due to
additive gene
effects=
Repeatability
proportion of phenotypic variance
due to all permanent effects
VA  VD  VI  VEP
re 
VA  VD  VI  VEP  VET
Contrast between
2
h
and re
repeatability > heritability
heritability
association between parent and
offspring
repeatability
association between
adjacent records on an
individual
.
Repeatability
only important for repeated traits
repeated traits
those measured more than
once
milk production
egg production
.
Repeatability
if repeatability = 1
next year’s record will be the
same (relative to mean)
as this year’s
if repeatability = 0
this year’s record tells us
nothing about future
records
.
Phenotypic correlation
association between actual
performance for two
traits
Genetic correlation
association between genetic
merit for two traits.
Genetic correlation
caused by
linkage
pleiotropy
genes that affect
more than one
trait
.
Genetic correlation
if traits have a non-zero
genetic correlation
selection for one trait yields
change in the other trait.
Beef cattle
BW WW ADG FAT REA
birth weight
.46
.01
weaning weight .42
.46
.04
.74
GENETIC
feedlot gain
.12 .20
-.05 .49
CORR.
fat thickness
.01
.18
-.30
rib eye area
.08
.20
-.30
PHENOTYPIC CORRELATION
SWINE
average daily gain
days to 230 pounds
backfat thickness
feed efficiency
loin eye area
ADG AGE
-.93
-.90
.20
-.18
-.65 .60
-.06 .03
BF
.22
-.20
.25
-.28
FE
-.70
.65
.34
LEA
-.10
.05
-.35
-.35
-.20
PHENOTYPIC CORRELATION
G
E
N
E
T
I
C