Question

In F2 generation of a mendelian dihybrid cross the number of phenotypes and genotypes are
A) Phenotypes-4 Genotypes-16
B) Phenotypes-9 Genotypes-4
C) Phenotypes-4 Genotypes-8
D) Phenotypes-4 Genotypes-9

Answer 1

The term F1 means ‘first filial generation’ and the term F2 stands for ‘second filial generation’. These terms were introduced by Gregor Johann Mendel who was also the first scientist to formulate the laws of inheritance. The term genotype refers to the genetic composition of an individual and phenotype refers to the observable characters.

Complete answer:

We know that Mendel formulated three laws of inheritance by carrying out an experiment with garden pea. He chose pea for his experiments due to various reasons such as- pea plant bred true, many varieties of them were available and their pollination could be easily manipulated. Mendel carried out the experiment with seven observable characteristics of pea plant- seed colour, seed texture, the height of the plant, flower colour, pod colour, pod shape and arrangement of flowers. He used two terms- dominant and recessive to distinguish between the two contrasting characters. Dominant characters were the ones who expressed themselves whenever present and recessive characters were ones that were expressed only when both the characters were recessive.

At first he crossed the two parent plants which gave rise to the F1 offspring. These F1 offspring were then crossed among themselves to give the F2 generation. So the F2generation is actually produced by the random union of the F1 gametes. Let us see the cross in which Yellow, Round (YYRR) is crossed with Green, Wrinkled (yyrr)

From the above cross it is clear that the four different phenotypes i.e yellow round, green wrinkled, yellow wrinkled and green round are obtained. The number of genotypes is 9.

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So the correct option is (D) Phenotypes-4 Genotypes-9.

Note:**** Mendel’s laws of inheritance gave the first basic idea of inheritance and was accepted worldwide, though later it was found that deviation from these laws occurs in some cases. The three laws of inheritance proposed by Mendel are- law of dominance, law of segregation and law of independent assortment. In the above case yellow, round is dominant over green, wrinkled.