Question

To determine the genotype of a tall plant of F2 generation, Mendel crossed this plant with a dwarf plant. This cross represents
A. Test cross
B. Back cross
C. Reciprocal cross
D. Dihybrid cross

Answer 1

Gregor Mendel chose pea plant to show that genotypic and phenotypic expression of the traits. He made many crosses to know the expression of traits of each level. To determine genotype of F2 generation, he crossed dominant trait with recessive parent to check the unknown genotype. He did it as test for the crosses he made earlier.

Complete step by step answer: Gregor Mendel is also known as father of genetics. He chooses seven contrasting characters of pea plant and experiments on them by making various crosses between different generations. First he did monohybrid cross by taking only one character and it that he observes the entire tall progeny's ratio as 3:1. In Dihybrid cross, he chooses two contrasting characters and makes a cross between them. In the 2nd generation, he gets the phenotypic ratio of 9:3:3:1. Then Mendel did a typical cross between dominant phenotype parents whose genotype is to be determined. He crossed it with recessive parents instead of self-crossing to know the zygosity of the former by analyzing proportions of offspring phenotypes. It is known as test cross because it shows the genotype of an unknown parent.

Dominant phenotype, unknown Genotype: PP or Pp?

Recessive Phenotype, known Genotype: pp

                X  

Pp	Pp
Pp	Pp
Pp	Pp
pp	pp

Entire population shows a dominant phenotype, if one parent is homozygous dominant.

Half of the population appears dominant phenotype and half appear recessive if one parent is heterozygous dominant.

If all the offspring have dominant phenotype, then parent will be homozygous, shows dominant and half shows recessive phenotype, then parent genotypes will not heterozygous dominant.Mendel crossed the dwarf plant with an unknown genotype of tall plant of F2 generation; this cross represents the test cross.
So, the correct answer is option A.

Note: Mendel also crossed a hybrid with one of its parents, to achieve offspring with genetic identity closer to the parents and named it as back cross. These experiments of Mendel are the basics of genetics. Codominance and incomplete dominance are some other phenomena observed later. Crossing of traits occurs at the time of gamete formation.