Chapter 13, Problem 1P

Summary Introduction

To review:

In the given question, it is asked to identify characteristics of homologous chromosomes synapsis which can be used to distinguish between two plant species. Plant species A (Diploid) possesses $\text{36}$ chromosomes and plant species B (Triploid) also possesses $\text{36}$ chromosomes.

Introduction:

Prophase-1 is a phase in the process of germ cell division (meiosis) in which duplicated chromosome gets condensed and aligns with their homologous chromosome. This pairing between two homologous partners is followed by a crossing over which results in genetic recombination (exchange of genetic material between pair of homologous chromosomes).

The organism which possesses a pair of homologous chromosomes in its somatic cell is termed as a diploid organism. Similarly, the organism possessing three homologous chromosomes in its somatic cell is termed as a triploid organism.

Explanation of Solution

According to the given information, species-A is diploid and possesses $\text{36}$ chromosomes; here, the possible number of pair of homologous chromosomes is $18$ and no unpaired or trivalent chromosome is present in prophase.

According to the given information, species-B is triploid and possesses $\text{36}$ chromosomes; here the possible number of triplets could be $12$ and prophase may possess an unpaired chromosome, a pair of homologous chromosome, and triplets.

Diagram-Triploid cell with unpaired chromosome, a pair of homologous chromosome, and trivalent.

Conclusion

In species-A, the possible number of pair of homologous chromosomes is $\text{36}$ and no unpaired or trivalent chromosome is present in prophase.

In species-B, the possible number of triplets could be $12$ and prophase may possess an unpaired chromosome, pair of homologous chromosome, and trivalent.