Meiosis Purpose of Meiosis To make gametes for

Meiosis

Purpose of Meiosis • To make gametes for sexual reproduction – To create diversity

What are gametes? – Gametes are “sex cells. ” • Sperm in males • Ova (eggs) in females. – Each gamete is haploid (contains only one copy of each chromosome instead of two). – Every gamete is completely unique.

Starting point • Only special cells can go through meiosis. – Spermatogonia – Oogonia

Where does meiosis occur? • In males, sperm are made in the testes. • In females, ova (eggs) are made in the ovaries.

Stages of Meiosis

Interphase • The stage between divisions • Consists of three steps: – G 1 – Cell growth – S – copying the chromosomes – G 2 – preparing to divide

Prophase 1 • • Chromosomes condense Nuclear envelope begins to dissolve Nucleolus disappears Tetrads form and crossing over occurs

Crossing Over • The process in which homologous chromosomes trade parts.

Homologous Chromosomes Matching chromosomes. • One from mom; one from dad.

Metaphase 1 • Homologous chromosomes line up in the middle

Anaphase 1 • Homologous chromosomes are pulled apart.

Telophase 1 • Two new nuclei form

Prophase 2 • Nuclear envelopes break down again

Metaphase 2 • Chromosomes line up in the middle

Anaphase 2 • Sister chromatids are pulled apart

Telophase 2 • 4 new nuclei are formed

Product of Meiosis • Each spermatagonia makes 4 sperm. • Each oogonia makes one ovum and 3 polar bodies.

Mendel’s Law of Segregation • An individual’s alleles separate randomly during meiosis.