CHAPTER 8 - RAMIFICATIONS OF GENETICS

Abstract

This chapter discusses the ramifications of genetics. The greatest effect of the development of genetics upon the breeding of animals of economic importance has been the replacement of phenotypic selection by genotypic. The modern genetic type of selection is based upon the idea that the best way of judging the qualities of parents is by assessing the qualities of their offspring. Individuals are selected as parents only if they produce offspring of the desired type. This type of selection is known as the progeny test or progeny selection. In the fowl, both males and females are selected for further breeding on the egg-production of their daughters. In cattle, a dairy sire is chosen on the records of his first six daughters. Genetics has shown that inbreeding increases homozygosity in the population, isolating pure lines, bringing to light characters that are based on recessive genes. In every individual of a population that has not been consistently inbred, there will be many recessive genes in the single dose and many of these will relate to characters that are disadvantageous or unwanted. Under a system of random mating, these recessive genes are carried along in the heterozygous state from generation to generation. But under any system of inbreeding, the heterozygotes in a population become less frequent and the homozygotes more frequent.