Question

What is the nature of offspring of a test cross?

Answer 1

The test cross is used under the law of dominance which comes under the Mendelian laws of genetics to determine the genetic composition of an individual which helps to identify the individual as homozygous or heterozygous.

Complete answer-
To carry out a test cross and in turn determine the genetic composition of an individual, the individual is bred with another individual who was homozygous for the recessive trait and the resulting offspring was studied. By this method, determination of the genotype of the individual is easy because the homozygous recessive allele individual can only pass on recessive alleles to the offspring. So the allele the other individual passes determines the phenotype of the offspring. Here two types of results are generally obtained from the test cross. First is if any of the offspring produced expresses the recessive trait then the individual is said to be heterozygous for the dominant allele and second is if all of the offspring expresses only the dominant trait then the individual is said to be homozygous for the dominant allele. Test crosses have wide application and are mostly used with two common model organisms Caenorhabditis elegans and Drosophila melanogaster.

Note:
Though the test cross is important in determining the genotype of an individual it has few limitations. Such as it is time consuming as some of the organisms need a long time for growth, it also requires a large number of organisms due to statistical reasons and they are not effective in cases of incomplete dominance.