PARAMETER GENETIKPARAMETER GENETIK

Genetic parametersGenetic parameters

(h(h2 2 , r dan r, r dan rG G ) )

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 Mean ? Variance ?

4. 0.5 9. 0.75

5. 0.75 10. 0.40

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(%) Trait Heritability (%)

Beef Cattle   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

Horses Backfat probe 40

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)

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 ?

R = (Vg + Vep)/ VP

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)

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.

Texas Longhorn cattle

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