Question

Which of the following statements correctly explains why gametes are considered to be haploid at the end of Meiosis I?

• A. Crossing over occurs in prophase I and this process only occurs in haploid cells
• B. Homologous pairs separate at the end of telophase I, making the cells haploid
• C. When tetrads line up along the metaphase plate in metaphase I, this creates haploid cells
• D. The homologous pairs pull apart at anaphase I, and this creates haploid cells
• E. Sister chromatids separate at the end of telophase I, making the cells haploid

Answer 1

Answer: (E)

Sister chromatids separate at the end of telophase I, making the cells haploid

Meiosis I is called the reduction division and includes the following stages:

1. Prophase I: It is the longest phase and is further divided into following stages.

(i) Leptotene- Chromosomes shorten, become thread like and visible as single structures.

(ii) Zygotene- Homologous chromosomes pair up by the process called synapsis and forms a complex bivalent structure.

(iii) Pachytene- Crossing over occurs between non sister chromatids of homologous chromosomes.

(iv) Diplotene- Dissolution of synaptonemal complex occurs and chiasma formation takes place. Chiasma is the result of the fact that the chromosomal parts begin to repel each other except in the region where these are in contact. It is a X-shaped structure.

(v) Diakinesis- This stage is marked by terminalisation of chiasmata. Chromosomes become more condensed and bivalent remain evenly distributed in the nucleus.

2. Metaphase I: The bivalents become arranged around the equator of the spindle attached by their centromeres.

3. Anaphase I: Spindle fibres pull homologous chromosomes towards the opposite poles of the spindle. This separates the chromosomes into two haploid sets with one set at each pole. It is the stage in which chromosome number becomes half.

4. Telophase I: The arrival of homologous chromosomes at opposite poles mark the end of meiosis I. It is followed by cytokinesis and two daughter cells are formed, each containing half the number of chromosomes as the parent cell.

Hence, gametes are haploid because reduction of chromosome number to half takes place during meiosis I.

So, the correct answer is 'Homologous pairs separate at the end of telophase I, making the cells haploid'.