Question

What is a test cross? Mention its significance.

Answer 1

Hint: A test cross is a method used in genetics to determine the genotype of an organism. It is calculated in a punnett square as it is done in normal Mendel’s crosses.

Complete answer: Across between an individual of unknown zygosity and a homozygous recessive individual is carried out in order to identify the zygosity of the unknown individual by examining the phenotypes of the offsprings. This type of cross is known as a test cross. The types of alleles of a gene present in an organism may be either dominant or recessive type. If both alleles in an organism are the same, then the organism is called homozygous and if the alleles are different, the organism is called heterozygous. This is called the zygosity. In a test cross, the homozygous recessive trait is contributed by the homozygous recessive parent and the other trait comes from the parent of unknown genotype. So, whatever trait comes from the parent of an unknown genotype will be seen in the offspring and then we will be able to identify the zygosity of the unknown parent. Significance of testcross:
A test cross is performed in order to determine the genotype of a dominant parent, i.e., whether it is a heterozygous or a homozygous dominant. On the basis of the results obtained, the ratios of the offsprings help us to predict that the parent has which type of genotype. If all the offsprings show the same phenotype, then the parent is a homozygous dominant. If there is 1:1 ratio in the phenotype of the offsprings, the parent is a heterozygous dominant.

Note: Test cross is of great significance to determine the genotype of an organism based on the expressed phenotypic characteristics. Apart from test cross, other types of crosses that are used in genetic studies include back cross, monohybrid cross, dihybrid cross, trihybrid cross, etc.