Meiosis Creation of sex cells

Diploid vs Haploid Diploid Haploid 2 copies of each chromosome All our body cells are diploid 2n Haploid one copy of each chromosome Our sex cells (sperm, egg) are haploid 1n *n= number of copies of chromosome*

Why Meiosis? Humans are ___________: 23 pairs of chromosomes Sex cells are ___________: contain 1 set of 23 chromosomes Fertilization of two _____________ (sperm and egg) create one ZYGOTE that is __________ Sexual reproduction creates a zygote that is genetically different than both its parents

Why Meiosis? Humans are DIPLOID: 23 pairs of chromosomes Sex cells are HAPLOID: contain 1 set of 23 chromosomes Fertilization of two SEX CELLS (sperm and egg) create one ZYGOTE that is DIPLOID Sexual reproduction creates a zygote that is genetically different than both its parents

First division Second division

Stages The stages look very similar to the stages of mitosis- a few differences: Meiosis I Homologous chromosomes pair (tetrad) and line up at equator Sister chromatids move to the SAME pole of the cell “Tetrad”

Stages Meiosis II Each daughter cell continues to divide to produce two haploid cells No replication of DNA between Meiosis I and Meiosis II

Increasing Genetic Diversity During Meiosis I two steps are key in increasing genetic diversity Crossing over: During Prophase I Homologous chromosomes exchange pieces of DNA 2. Independent assortment: During Anaphase II Homologous chromosomes and/or sister chromatids are randomly assigned to each daughter cell

Crossing Over

Independent Assortment

Video Meiosis

Stages of Meiosis Cut out the stages and paste them in the correct order Label Meiosis I and Meiosis II Label each stage Colour each chromosome and track it through the stages Indicate where crossing over occurs Indicate where independent assortment occurs