Lecture nine

Meiosis and Gene Linkage

PMAT

Chromosome Number

Diploid

Homologous

Haploid

Phases of Meiosis

Meiosis

By the end of meiosis II, the diploid cell that entered meiosis has become four haploid cells

What Happens When It Goes Wrong?

Meiosis I: Prophase

Tetrad

O Crossing Over

Meiosis I: Metaphase

Spindle fibers attach to the chromosomes

Meiosis I: Anaphase

The fibers pull the homologous chromosomes toward opposite ends of the cell

Meiosis I: Telophase and Cytokinesis

Nuclear membranes form. The cell separates into two cells

These two cells enter Meiosis II

Meiosis II: Prophase

Unlike the first division, neither cell goes through a round of chromosome replication before entering meiosis II

Each of the cell’s chromosomes has 2 chromatids

Meiosis II: Metaphase

Chromosomes line up in the center of each cell

Meiosis II: Anaphase

The paired chromatids separate and move toward opposite ends of the cell

Meiosis II: Telophase and Cytokinesis

Each cell separates into two cells - meaning four haploid cells all together

Gamete Formation

In male animals, meiosis produces four haploid sperm cells

However, the cell divisions at the end of meiosis are uneven in females, so that only a single cell receives most of the cytoplasm

Mitosis vs. Meiosis

Gene Linkage

It is the chromosomes that assort independently, not the individual genes

Mendel did not discover gene linkage (Morgan did)

Gene Maps