Page 172 - Agriculture_Form_Three

Agriculture for Secondary Schools

Disadvantages of mating related animals
(a) It increases homozygosity state.
(b) The undesirable characteristics are increased in the progeny if the undesirable

gene segregation occurs.
(c) It increases mortality rate and hereditary abnormalities in the farm.
(d) Breeding and reproduction failures usually increase.

Mating of unrelated animals: This is also termed as out breeding which is further
divided into crossbreeding, outcrossing, backcrossing and upgrading.

Crossbreeding: This refers to mating animals of different breeds, for example, mating
a Tanzanian Short Horn Zebu cow with a Friesian bull. The system is generally used
for production of new breeds.

Outcrossing: This refers to mating animals from a different farm far related. It is

used when a farmer wants to introduce some desirable genes in the herd within the
same breed. Outcrossing has become common in production of pigs and hybrid
chickens. It has also been used in the production of beef cattle and to some degree
in dairy cattle.

Backcrossing: This is breeding of a crossbred individual back to one of the pure
parent races which were used to produce it. This method is commonly used when
you want to increase the genetic constitution of one breed.

Upgrading: This is a practice of breeding sires of pure improved breeds to very
ordinary female breeds and their offspring, generation after generation. In this
method, purebred bulls of certain improved breeds are used continuously. Continued
use of the good purebred sires for only a few generations is what is required to bring
the herd to the point at which it has all the characteristics (appearance, actions,
practical value) of pure breeds.

In selecting unrelated animals to mate, it is important to understand its advantages

and disadvantages.

Advantages of mating unrelated animals
(a) It is a useful means of introducing desirable characters into a breed where they
never existed before.
(b) It increases genetic diversity, thus reducing the probability of an individual

being subject to diseases or genetic abnormalities.

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