Question

Define the Test cross.

Answer 1

Hint: This cross has a ratio of 1:1:1:1 phenotypic ratio which is the classic Mendelian ratio for this cross in which the alleles of the two genes assort independently into gametes.

Complete answer:
The phenomenon of test cross was first introduced by Gregor Mendel. When the $F_1$ hybrid is crossed back only with the homozygous recessive parent, this is called the test cross. This is used to determine the genotype of an individual with a dominant character. If all the offspring has Yy, then the parent is YY. If half the offspring are Yy and half offspring are yy, then the parent is Yy.

Additional Information: Test cross and Back cross:
Test cross and backcross are two of the types of crosses introduced by the scientist Gregor Mendel. In the test cross, a dominant phenotype is crossed with the homozygous recessive genotype in order to discriminate between homozygous dominant and heterozygous genotypes, while in backcross, the F1 is crossed with one of the parents or genetically identical individual to that of the parent. The main difference between the test cross and the backcross is that the test cross is used to discriminate the genotype of an individual which is phenotypically dominant whereas a backcross is used to recover an elite genotype from a parent which bears an elite genotype.

Note: Mendelian inheritance was originally proposed by Gregor Johann Mendel in 1865 and 1866. These were rediscovered in 1900 and were made infamous by William Bateson. The third law is the Law of dominance in which one allele is dominant over the other. The basis of Mendel’s law is the crossing of two parents leading to resultant offspring. Its phenotypic ratio is similar to the phenotypic ratio of the law of segregation which is 3:1.