Question

Genotype of hybrid is known by crossing

• A. F${}_2$ progeny with female parent
• B. F${}_1$ x F${}_1$
• C. Crossing F${}_1$ with recessive parent
• D. F${}_2$ with recessive parent

Answer 1

The correct option is C Crossing F${}_1$ with recessive parent

Testcross is a cross of any genotype with a recessive homozygote. The 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; this makes option A and B wrong. If a gamete from the hybrid contains a recessive allele, the resulting progeny will have a recessive phenotype. But if it contains a dominant allele, the progeny will have a dominant phenotype. Therefore, genotypes of the gametes from the hybrid determine the phenotypes of the offspring in a test cross. The F${}_1$ hybrid is heterozygous for all genes which make it best to cross it with the recessive individual. This makes option C correct. A cross between F${}_2$ and recessive parent is test cross provided that the F${}_2$ plant is phenotypically dominant; thus it does not always hold true for test cross; option D is wrong.