Lecture on Meiosis I

Overview

• Focus on Meiosis I, beginning with Prophase I.
• Unique aspect: Chromosomal crossover, adding genetic variation.

Prophase I

• Similar to mitosis: nuclear envelope disappears, chromosomes condense.
• Unique: Chromosomal crossover occurs where homologous chromosomes exchange genetic material (alleles), leading to variation in offspring.

Metaphase I

• Chromosomes line up along the metaphase plate.
• Chromosomes composed of two sister chromatids aligned with homologous pairs.
• Centrosomes play a significant role by organizing microtubules to attach to chromosomes at the kinetochores.

Anaphase I

• Homologous chromosomes pulled apart but sister chromatids remain together (difference from mitosis).
• Random assortment of homologous chromosomes adds further genetic variation.
• Involves motor proteins and dynamic changes in microtubules to facilitate movement.

Telophase I

• Homologous chromosomes are fully separated.
• Chromosomes begin reverting to chromatin state.
• Nuclear membrane reforms.
• Cytokinesis begins leading to cell division into two haploid cells.

Key Points

• Meiosis I leads from one diploid germ cell to two haploid cells.
• Each haploid cell contains two chromosomes, each with two sister chromatids.
• Sets the stage for Meiosis II, similar to mitosis, which will separate sister chromatids.
• Overall, meiosis contributes to genetic diversity in gametes.