Question

What is a 'test cross'? Explain significance of a test cross.

Answer 1

The crossing of an organism, with an unkown genotype, to a homozygous recessive organism (tester). A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual.

Complete answer:
To decide whether the progeny is homozygous or heterozygous for a character under consideration, the crossing of an F1 progeny with a double (homozygous recessive paternal progeny is performed. The above-discussed process is called as test-cross.
Significance- If it is heterozygous or homozygous dominant, the test cross is used to determine the genotype of a dominant parent. It can be estimated that the parent has the genotype, on the basis of the results obtained in the ratio of the offspring. If all the offspring are of the same allele, so the dominant parent is homozygous. The parent is heterozygous dominant whether there is a 1:1 ratio in the phenotype of the organisms.

There are also risks to evaluating crosses. As certain species take a long growing period in each generation to display the required phenotype, it can be a time-consuming process. Owing to numbers, a vast number of offspring are often expected to provide accurate records. Only if supremacy is complete are test crosses useful. Incomplete supremacy is where the dominant allele and the recessive allele fall together in the offspring to create a combination between the two phenotypes. Variable expressivity is where a single allele generates a number of phenotypes that are often not found in a cross examination.

Note: To differentiate between homozygous dominant and heterozygous genotypes, a dominant phenotype is crossed with the homozygous recessive genotype in the test cross. The F1 is crossed with one of the parents in the backcross, or genetically related to the parent.