How do alleles of each gene separate into different haploid daughter nuclei during meiosis?

Sourav PanNovember 8, 2024

Answered

During meiosis, alleles of each gene separate into different haploid daughter nuclei through a highly coordinated process involving two sequential divisions: meiosis I and meiosis II. This separation is crucial for ensuring that gametes contain only one allele of each gene, maintaining genetic diversity and stability across generations.

Meiosis Overview

Meiosis consists of two main stages:

• Meiosis I: This is a reductional division where homologous chromosomes (each consisting of two sister chromatids) are separated into two daughter cells.
• Meiosis II: This is an equational division similar to mitosis, where sister chromatids are separated into four haploid daughter cells.

Key Steps in Allele Separation

1. Homologous Chromosome Pairing:
   • During prophase I, homologous chromosomes pair up and form structures called bivalents or tetrads. Each bivalent contains four chromatids (two from each homolog) .
   • This pairing is facilitated by the synaptonemal complex, which helps align homologs and allows for genetic recombination through crossing over .
2. Crossing Over:
   • While paired, segments of DNA may be exchanged between non-sister chromatids of homologous chromosomes during crossing over. This process creates new combinations of alleles on the chromatids, enhancing genetic diversity .
   • The points where crossing over occurs are called chiasmata, which help hold the homologous chromosomes together until they are ready to segregate .
3. Segregation During Meiosis I:
   • At metaphase I, bivalents align at the metaphase plate, and spindle fibers attach to kinetochores on the chromosomes.
   • During anaphase I, the spindle fibers pull the homologous chromosomes apart, separating them to opposite poles of the cell. Each daughter cell receives one chromosome from each homologous pair, thus becoming haploid (containing one allele for each gene) .
4. Sister Chromatid Separation in Meiosis II:
   • After meiosis I, the two haploid cells enter meiosis II without further DNA replication. During metaphase II, the chromosomes line up again at the metaphase plate.
   • In anaphase II, the sister chromatids are finally separated and pulled to opposite poles, resulting in four haploid daughter cells at the end of telophase II and cytokinesis .