Cell Division Meiosis

Chromosome Number of Different Species Homo sapiens (human) 46 Mus musculus (house mouse) 40 Zea mays(corn or maize) 20 Drosophila melanogaster (fruit fly) 8 Xenopus laevis (South African clawed frog) 36 Caenorhabditis elegans (microscopic roundworm) 12 Saccharomyces cerevisiae (budding yeast) 32 Canis familiaris (domestic dog) 78 Arabidopsis thaliana (plant in the mustard family) 10 Muntiacus reevesi (the Chinese muntjac, a deer) Muntiacus muntjac (its Indian cousin) 6 Myrmecia pilosula (an ant) 2 Parascaris equorum var. univalens (parasitic roundworm) Cambarus clarkii (a crayfish) 200 Equisetum arvense (field horsetail, a plant) 216

Chromosome Vocabulary DNA Doubles during interphase (S phase) Chromosome Forms during prophase Become sister chromatids

Homologous Chromosomes: Members of a pair of chromosomes One – Mom One – Dad Same size Same shape (centromere location) Same number and type of genes

Homologous Chromosomes: Specific gene information may differ (brown eyes from mom, blue eyes from dad)

Homologous Chromosomes: Same banding pattern when stained and viewed under a microscope. Bands DO NOT indicate genes.

Types of Chromosomes: Humans have 23 pairs of chromosomes.

Types of Chromosomes: 2 Types: Autosomes: Members of chromosome pairs #1-22.

Types of Chromosomes: 2 Types: Sex Chromosomes: Members of chromosome pair #23 Females = XX Males = XY

Sex Chromosomes ALL pairs are homologous in females because they have two X chromosomes The sex chromosomes of males are NOT homologous, they have one X and one Y

Diploid vs. Haploid Diploid: two sets of chromosomes Each chromosome has a homologous pair– there is one from each parent! They have the same type of genes but are not identical Human body cells: 23 PAIRS  46 total

Diploid vs. Haploid Haploid: one set of chromosomes Why would you want just one set of chromosomes in a cell? SEXUAL REPRODUCTION! Human gametes: 23 total

Why do we need meiosis? Meiosis is necessary to halve the number of chromosomes going into the sex cells Gametes are haploid (1n) + 1 N sperm 1 N egg 2N zygote

Why do we need meiosis? + Fertilization Male and female sex cells will provide ½ of the chromosomes each Offspring has genes from both parents 1n + 1n = 2n + 1 N sperm 1 N egg 2N zygote

Video Clip Worksheet 17: Meiosis Overview

Meiosis Summary Two divisions - Meiosis 1: - like mitosis, but not quite - creates 2 cells (haploid) - Meiosis 2: - divides again - creates 4 gametes (haploid)

Meiosis Summary Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original # of chromosomes

Meiosis I – Prophase I Nuclear envelope dissolves

Meiosis I – Prophase I Tetrads form Crossing Over Homologous pair links together Crossing Over

Crossing Over in Prophase I Homologues break at identical locations, Rejoin opposite partners Occurs randomly several times on every chromosome Results in mixing of the genes you inherited from your parents Crossing over is NOT a mutation

Meiosis I – Metaphase I Tetrads line up in middle Spindle fibers attach Independent Assortment

Independent Assortment Metaphase I Principle of Independent Assortment—Genes for different traits (on different chromosomes) can separate independently of each other. --Happens because homologous pairs line up in random order on random sides during Metaphase I

Meiosis I – Anaphase I Fibers pull homologous chromosomes apart Sister chromatids are still connected! (2 X’s are separating from each other)

Meiosis I – Telophase I Cell separated into two cells Nuclear membrane forms

Meiosis II – Prophase II Nuclear membranes dissolve New spindle fibers form

Meiosis II – Metaphase II Sister chromatids connect to spindle fibers Line up in the middle

Meiosis II – Anaphase II Sister chromatids separate

Meiosis II – Telophase II Cells divide Now there are 4 haploid cells!

Meiosis I Meiosis II

Steps of Meiosis I and II

Video Clip Worksheet 18: Animal Cell Meiosis

http://www.johnkyrk.com/meiosis.html

Cell Division Products of Mitosis: Two identical cells Somatic cells AKA body cells Diploid Products of Meiosis: Four different cells Gametes AKA sex cells Haploid

Comparing Meiosis and Mitosis

Your Turn! Mitosis and Meiosis Worksheet