Question

One chromosome of a homologous pair carries the genes J and K. The other chromosome of the pair carries the genes j and k at corresponding loci. Crossing over results in exchange of chromosome segments and production of gametes with new combinations of genes. A recombinant type gamete resulting from this crossover might contain:
A. Genes J and K
B. Genes j and K
C. Genes J and j
D. Genes j and k

Answer 1

Hint: Crossing over leads to the exchange of genes from chromosomes. This recombinant gene is used in gamete formation. The gamete containing the genes from both chromosomes is the recombinant one.

Complete Step by Step Answer:
Homologous chromosomes have similar characteristics. They are approximate of the same length, their centromere position is also similar. They have the same staining pattern. The genes for the same characteristic are located at similar positions. One chromosome is obtained from the male gamete and the other from the female gamete. Here genes J and K are present on one chromosome and their allele j and k is present on their homologous chromosome.

Crossing over results in an exchange of chromosome segments and the production of gametes with new combinations of genes. It occurs in the prophase I stage of meiosis. In crossing over, the exchange of genetic material between non-sister chromatids of homologous chromosomes, that is recombination of gametes takes place. This process is seen during gamete formation.
During crossing over, some part of chromosome one is exchanged with some part of chromosome two. Hence some genes present on one chromosome will be exchanged with chromosome 2. In this case, gene K is exchanged with gene k present on another chromosome. The resulting recombinant genes will have genes J and k, and the other chromosome will have genes j and K.

Hence, The correct option is B.

Note: In crossing over, not all chromosomes are recombinant. Only 50% of the chromosomes become recombinant. Others are the same as the parental chromosomes, that is J and K on one chromosome and j and k on the other.