Inbreeding & Cross Breeding | Biology for Grade 12 PDF Download

ANIMAL BREEDING

Animal breeding aims at improving the genotypes of animals to make them more useful to us. 

The chief objectives of animal breeding may be summarized as follows :

(i) improved growth rate.

(ii) increased production of milk, meat, egg, wool, etc.

(iii) superior quality of resistance to various diseases.

(vi) increased or, at least, acceptable reproduction rate, etc.

(v) increased productive life, and

A variety of strategies have been used for breeding of animals. The main approaches for animal breeding, viz., inbreeding, out crossing and inter-specific hybridization, are briefly described below, based mainly on the breeding work with cattle.

Inbreeding :-

All domesticated animals have male and female individuals. As a result, they are strictly cross-fertilised, and highly heterozygous. Each domesticated animal species consists of several distinct breeds that differ from each other in several morphological and other features. You are familiar with the important breeds of cows, buffaloes, poultry, etc. Animals belonging to a single breed differ from each other in genotype because of the mode of their reproduction and their heterozygous nature. Therefore, mating between animals of the same breed provides opportunities for genetic improvement.

The breeding strategy based on inbreeding is as follows. Superior cows and superior bulls of the same breed are identified and mated in pairs. The progeny obtained from such mating are evaluated and superior males and females are identified for further mating. A superior female, in the case of cattle, is the cow that produces more milk or lactation. On the other hand, a superior male is that bull, which gives rise to superior progeny as compared to those of other males. 

Inbreeding, as a rule, increases homozygosity.

Advantage :

Inbreeding exposes harmful recessive genes that are eliminated by selection. It also helps in a accumulation of superior genes and elimination of less desirable genes. Therefore, this approach increases the productivity of inbred population. Practically every breed was developed by some type of inbreeding

Disadvantage :

But continued inbreeding, especially close inbreeding, usually reduces fertility and even productivity(inbreeding depression). Whenever this becomes a problem the selected animals of the breeding population should be mated with such superior animals of the same breed that are unrelated to those in the breeding population.

Cross-breeding :-

In this strategy, superior males of one breed are mated with superior females of another breed. Cross-breeding allows the desirable qualities of two different breeds to be combined in a single breed. The progeny animals may themselves be used as hybrids for commercial production. Alternatively, they may be subjected to some form of inbreeding and selection to develop new stable breeds that may be superior to the existing breeds. Many new animal breeds have been developed by this approach.
Progeny produced through cross-breeding may be mated according to various schemes to achieve specific objectives. For example, cows of an inferior breed may be mated to bulls of a superior breed. In each successive generation, the progeny cows are mated to the bulls of the same superior breed that was used in the original cross. Thus, in 6-7 generations, the progeny will be almost similar to the breed of bulls used for the mating. But these progeny would retain some original advantageous conditions, etc., of the other breed from which the cows were used in the original mating.

Interspecific Hybridization :-

In this strategy, male and female animals of two different species are mated. The progeny obtained from such a mating are usually different from both the parental species. In some cases, the progeny may combine desirable features of both the parents, and may be of considerable economic value. An example of this type is mule, which is produced from a cross between female horse (mare) and male donkey. Mules are sturdier and hardier than their parental species, that are well suited for hard work in difficult terrains like mountainous regions.