Crossbreeding

11 important questions on Crossbreeding

What is the equation for heterosis?

Heterosis%= 100% * (crossbred mean - mean of parents)/ mean of parents

What can be motivation for crossbreeding?

- Heterosis
- To benefit from direct and maternal heterosis
- To exploit the complementairty of breeds or lines:  combinatin of the charasteristics of two breeds or lines is favourable
- Crossbreds combine characterstics that cannot easily be improved simultaneously in a breed
- Protection of the genetic improvement in the selection lines of commercial companies

What is direct heterosis?

Orginates from the genes of the animal itself
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What is maternal heterosis?

Originates from the genes of the mother. The genes of the mother may affect the individual thorugh the environment provided by the mother

What are the several crossbreeding systems?

- Two-way cross (pure-breed cross)
- Three-way cross
- Four- way crossess
- Two-way rotation (crisscross)
- Three-way rotation (crisscross)
- Introgression
- Grading-up
- Creating synthetic breed

What is the three-way cross?

Two way cross females (f1s) are crossed to a purbred male of a third breed

What is the four-way crosses?

Two-way cross females (f1's) are brossed to crossbred males of a third and a fourth breed.

What is two-way rotation (crisscross)?

The start is similar to backcrossing. Females of breed A are crossed with males of breed B. Teir female offspring (f1) are backcrosses with a male of breed B. Their female offspring (f2) are crossed with a male of breed A. Their female offsping (f3) are crossed with a male of breed B etc.

What is three-way rotation (crisscross)?

Females of breed A are crossed to males of breed B. Their emale offspring (f1: AB) are crssed with a male of breed C. Their female offspring (f2; 25%A-25%B-50%C) are crossed then with a male of breed A. Their female offfspring are crossed with a male of breed B etc.

What is creating a synthetic breed?

Two breeds are crossed and males and gemales of the f1 are reciprocally mated

When is full heterosis obtained?

When at each locus one of both alleles descends frm one line and the other allele from the other line

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