Question

How many types of gametes are expected from a plant with genotype Pp Qq, provided there occurs independent assortment?
(A) 4
(B) 8
(C) 2
(D) 1

Answer 1

According to Mendel’s Law of Independent Assortment, the different types of characters present in plants are assorted independently during inheritance. This conclusion is based on ${F_2}$ – generation of dihybrid cross.

Complete answer:
In a plant with genotype Pp Qq, both the characters recombine independently from each other during gamete formation in ${F_1}$ generation. Factor (P) of pair factor Pq is having equal chance with (Q) factor or (q) factor of gametes during recombination to form two different types of gametes (PP) and (pp). Similarly, (q) factor also has an equal chance with (P) factor and (p) factor of gametes during recombination to form two different types of gametes (Pq) and (pq). Thus, a total four types of gametes are formed which are (PQ), (Pq), (pQ), and (pq).

Therefore the correct option is (A) 4.

Additional Information: Mendel concluded three postulates as a result of Monohybrid cross i.e Postulate of paired factors, Postulate of Dominance and Law of segregation. Incomplete dominance and codominance are the two exceptions of the Law of Dominance. Law of segregation does not have any exception.

Note: An exception to the Law of Independent assortment is ‘Linkage’. Linkage is known as collective inheritance of character. It can be represented in a hybrid plant. For example, in case of linkage in dihybrid Pp Qq, only two types of gametes are formed i.e. PQ and pq. The theory of linkage states that the Linked genes are linearly located on the same chromosome and get separated if crossing over takes place between them. All genes which are present on one pair of homologous chromosomes form one Linkage group. Genes which are located on one pair of homologous chromosomes inherited together and so, are considered one Linkage group.