AGB 211: Livestock and Poultry Breeding (2+1)

COEFFICIENT OF INBREEDING

Inbreeding increases homozygosity and decreases heterozygosity. The average percentage increase in homozygosity or decrease in heterozygosity in an inbred animal in relation to an average animal of the same breed or population is known as coefficient of inbreeding symbolised by ‘F’. It ranges from 0 to 100.

The degree of inbreeding inb any individual may be calculated by using the formula Wright 1921.

Fx = [(1/2)n1+n2+1 (1+FA)]

Where,

Fx     =  Coefficient of inbreeding of X.

=  Summation

n1      =  No. of generation from the sire of X back to the same common ancestor

n2      =  No. of generation from the dam of X back to the same common ancestor

FA     =  Coefficient of inbreeding of the common ancestor

When common ancestor is not inbred then

Fx = [(1/2)n1+n2+1]

To calculate the inbreeding coefficient the pedigree should be known. The pedigree can be represented in two ways.

• Bracket form
• Path diagram (Arrow diagram)

In the arrow style, each common ancestor is included only once, with lines drawn to each of his or her offspring in the pedigree. These lines represent the paths of inheritance by which genes are transmitted.

To calculate the Fx

• Convert the bracket form of pedigree to path diagram
• Draw arrows from parents to offspring
• Besure that each individual appears only once in the path diagram

Full sib mating (Brother X Sister)

• Common ancestor n1 n2 contribution
• C 1 1 (1/2 )1+1+1 =( ½)3 = 12.5 %
• D 1 1 (1/2 )1+1+1 =( ½)3 = 12.5 %
• Sum = 25.0 %

Half – sib mating

• Common ancestor n1 n2 contribution
• D 1 1 (1/2 )1+1+1 =( ½)3 = 12.5 %
• Fx = 12.5 %

Parent offspring mating Father X Daughter, Mother X Son

• Common ancestor n1 n2 contribution
• Common ancestor n1 n2 contribution
• A 0 1 (1/2 )0+1+1 =( ½)2 = ¼ = 25 %

The coefficient of inbreeding ( Fx = 25 or 12.5 or 25 % in the egs) means that the animal “X” is 25 % or 12.5 % or 25 % less heterozygous than the animals in the herd.

Let us see an example with an inbred common ancesstor.

Common ancestor are

• B as sire of X and I
• B as sire of X and J
• E as dam of B and J
• F as dam of D and E

B ais the only common ancestor which is already inbred.

FB = (1/2) 1+1+! = (1/2)3 = 0.125 or 12.5%

By using formula

Fx = [(1/2)^n₁+n₂+1 (1+FA)]

The coefficient of inbreeding Fx can be calculated as follows