Question

Mating of an organism to double recessive for determining homozygosity or heterozygosity is called as

• A. Reciprocal cross
• B. Back cross
• C. Dihybrid cross
• D. Test cross

Answer 1

The correct option is D Test cross

Two crosses between the same pair of genotypes/phenotypes in which the sources of gametes are reversed in one cross are called reciprocal cross; a cross between yellow and round seed female plant with green wrinkled seed male plant followed by a cross between yellow and round seed male plant with the green wrinkled seed female plant. It is done to confirm if the results of the cross are affected by the sex of parents which makes the option A wrong. Back cross is a cross between F${}_1$ hybrid and one of the parents to deduce the genotype of both parents and the hybrid; option B is wrong. A cross between two genotypes that are heterozygous for two genes is called as dihybrid cross. It is done to study if inheritance of two genes, under study, follow independent assortment or they show linkage; option C is wrong. A test cross is performed to determine the genotype of a dominant parent if it is a heterozygous- or homozygous-dominant. Gametes of the recessive homozygote contain only recessive alleles and therefore alleles that the gametes of the other parent carry will determine the phenotypes of the offspring. If a gamete from the tested genotype contains a recessive allele, the resulting F${}_1$ organism will have a recessive phenotype. But if it contains a dominant allele, the F${}_1$ organism will have a dominant phenotype. Therefore, test cross requires one double recessive parent and another parent with at least single copy of dominant allele so that the genotypes of the gametes from the organism being tested can determine the phenotypes of the offspring; option D is correct.