Transcript What is heritability?

PARAMETER GENETIK
Genetic parameters
(h2 , r dan rG )
Variable/ trait :
1. Coat color
2. Horn/hornless
3.
Animal power (work/
plough in paddy field)
4. Milk production, number
of progeny
Genetic : breed, genetic group, linebred
Environment : feed, food, wind, humidity,
temperature, light, insect
G x E interaction : breed-level of feed,
group-Temp.humid
GENETIC PARAMETER (PARAMETER GENETIK )
(heritabilitas/ heritability, ripitabilitas/ repeatability, korelasi
genetik/ genetic correlation)
What is heritability?
Heritability can be defined as the
efficiency of transmission of superiority
(or inferiority) of a trait from parents to
offspring. It is usually expressed as a
percentage ranging from 0%-100%, or
as a decimal number ranging from 0 to
1.
Trait :
- Quantitative traits (milk,
meat, egg, work, wool,
power, IQ etc)
-A matter of variance :
VP = VG + VE + VGxE
P = G + E + GxE
Fenotipe = genetik + lingkungan +
interaksi genetik-lingkungan
HERITABILITAS
Traits that are 100% heritable
If a trait is 100% heritable, then the full expression of the parents’ trait will
be expressed in or by the off-spring. A trait that is 100% heritable would truly be
a case of 'what you see is what you get' as 100% of the trait or genotype will be
expressed in the animal’s phenotype, or the way the animal looks.
There are a great many other traits that we take for granted as being 100%
heritable. Under normal circumstances, many physical traits such as number of
fingers on a human hand or the number of legs on the body of cattle are 100%
heritable. A person's phenotype may be affected by the environment, for
example, if an arm is amputated as a result of an accident, but the genes that an
amputee carries in his/her gametes mean that any offspring will still be born with
both arms.
Other physical traits, such as height in humans or weight gain in cattle, are
not 100% heritable. If this were the case every brother or sister in any species
would be exactly the same height. The heritability of height is less than 100%.
Heritability formula :
h2 = VG/ VP
V : variance (δ2)
Data daily weight gain in cattle (kg) :
1.
0.6
6. 0.45
2.
0.7
7. 0.55
3.
0.8
8. 0.65
4.
0.5
9. 0.75
5.
0.75
10. 0.40
Mean ? Variance ?
Mean : X = 6.15/10 = 0.615 kg
Variance : s2 = [(0.6-0.615)2 + (0.7-0.615)2 + …… (0.40-0.615)2]/9
= 0.0189
s = 0.1375
Trait
Heritability(%)
Beef Cattle
Trait
Heritability
(%)
Dairy Cattle
Calving interval
10
Services per conception
5
Age at puberty
40
Birth weight
50
Scrotal circumference
50
Milk production
25
Birth weight
40
Fat production
25
Weaning weight
30
Protein
25
Post-weaning gain
45
Solids-not-fat
25
Yearling weight
40
Type score
30
Yearling hip frame size
40
Teat placement
20
Mature weight
50
Mastitis susceptibility
10
Carcass quality grade
40
Milking speed
30
Yield grade
30
Mature weight
35
Eye cancer
30
Excitability
25
Sheep
Poultry
Number born
15
Age at sexual mature
35
Birth weight
30
Total egg production
25
Weaning weight
30
egg weight
40
Mature weight
40
Body weight
40
Post weaning gain
40
Shank length
45
Fleece weight
40
Egg hatchability
10
Fibre diameter
50
Livability
10
Face covering
55
Loin eye area
55
Swine
Carcass fat thickness
50
Litter size
10
Weight of retail cuts
50
Birth weight
5
Post weaning gain
30
Backfat probe
40
Horses
Withers height
45
Carcass fat thickness
50
Pulling power
25
Weaning weight
15
Racing (log $earnings)
50
Loin eye area
45
Trotters (log $earnings)
40
Percent lean cuts
45
Jumping ($ earnings)
20
Dressage ($ earnings)
20
Goats
Cutting ability
5
Milk production
30
Mohair production
20
REPEATABILITY (R)
R = (Vg + Vep)/ VP
1.
The ability to repeat expression of particular trait on the future/ next
production period
2.
Correlation between (2 periods), or among (3 or more periods)
measurements
3.
Examples :
Cow no. :
1st lact. (100kg) :
2nd lact. (100kg) :
1
50
55
2
60
62
3
58
59
4
62
62.5
5
56
58
R?
GENETIC CORRELATION ( rG )
1.
Correlation between 2 traits on different generation
- trait 1 on parent generation and trait 2 on the next
generation
2.
It is caused by :
- pleiotropic gene (1 gene influence 2/ more traits)
- linkage of genes (unreal genetic correlation)
3.
Examples :
- milk yield with % fat (negatif)
- weaning weight with post weaning gain (positif)
- birth weight with litter size (in swine/ negatif)
Texas Longhorn cattle
Some traits, such as hair color, are determined by only a few genetic loci. The
inheritance of such traits is relatively easy to predict, and the different phenotypes
tend to occur in qualitatively distinct states (such as "black" and "red"). Other
traits, usually called quantitative traits, may be influenced by many different genes,
and the continuous variation observed often has a relatively large environmental
component. Horn length in Texas Longhorns is an example of a quantitative trait.
This article discusses the basics of selection for quantitative traits, using horn
length as an example.
Most traits of interest in Texas Longhorns are controlled by many different genetic
loci, and many of these traits are also influenced by the environment in which the
animal was raised and now lives. These traits typically are expressed along a
continuum, rather than as a series of discrete states. For instance, the amount of
milk produced by a cow clearly is influenced by her genetics, but it is also
influenced by environmental factors (such as how much and what kind of food is
available to the cow). Moreover, cows vary along a continuum in how much milk
they produce. Such traits are called quantitative traits.
Other trait : the tail thickness of Fat Tailed Sheep (Domba Ekor Gemuk) is
quantitative trait, so h2 of this trait can be measured.
Homework :
Search some kinds of quantitative traits on internet, textbooks or journal
See you next week
Wassalam