Question

What is the cross between the progeny of F1 and the homozygous recessive parent called? How is it useful?

Answer 1

Hint: Test cross is the cross between the progeny of F1 and the homozygous recessive parent. Test cross is often confused with a back cross.

Complete answer:
The F1 hybrid, also called the filial 1 hybrid, is the first generation of offspring produced by the cross of two different parental types. The two parental types are distinctively different from each other and are homozygous for their traits. While one parent has the dominant allele for a gene, the other parent has the recessive allele of the gene. The F1 hybrid will have- one dominant allele and one recessive allele. They will show the phenotype of the dominant allele due to the law of dominance. In the F1 generation, all the offsprings produced are similar to each other- genotypically and phenotypically. The F1 hybrids are self- crossed with each other to obtain the F2 generation or progeny of F1. The hybrids of the F2 generation have different phenotypes and genotypes. Their phenotypic ratio is 3:1, and their genotypic ratio is 1:2:1. Genotype gives the genetic constitution of the cell whereas the phenotype is the external appearance or observable physical traits.
Here, one offspring is homozygous dominant, one is homozygous recessive, and two are heterozygous dominant.

A test cross is a cross between the hybrids of F2 generation or progeny of F1. In this cross, the F2 hybrid is crossed with the homozygous recessive parent of the parental generation. The offsprings or hybrids produced from this cross are studied. Their phenotypic ratio helps us to identify the genotype of the F2 offspring.

Thus, a test cross is performed to find out the genotype of a F2 hybrid. It is used to distinguish between the homozygous dominant and heterozygous dominant offspring. While the homozygous dominant hybrid will produce all the offsprings that show the dominant phenotypes, the heterozygous dominant hybrid will produce half offsprings with dominant phenotype and the other half with a recessive phenotype.
The test cross was first performed by- Gregor Mendel.

Note: Test cross is often confused with a back cross. A cross that is done between a hybrid offspring and a parent is called a back cross. The parent can be- any one of the two parents. It is not specific like a test cross and is done to obtain offsprings that are genetically closer to their parents.