Meiosis! Chapter 10.2

Meiosis: cell division to produce GAMETES!! Sperm= male gamete (haploid) Egg= female gamete (haploid)

Vocabulary! (needed before we can discuss meiosis) Gene—section of DNA that codes for a trait Allele– a version of a gene. Ex? Chromatin– uncoiled, stringy DNA Chromosome– piece of packaged DNA that is easier to move around.

Chromosome CENTROMERE – the place where two sister chromatids are attached.

Vocabulary Homologous Chromosomes— paired chromosomes that have genes for the same traits (in the same order) One homologous chromosome of each pair comes from mom One homologous chromosome of each pair comes from dad

Vocabulary Haploid—gametes which have half the number of chromosomes - are labeled 1N (1N= 1 set of chromosomes). Diploid—A full set of chromosomes from each parent (2N = 2 sets of chromosomes) *Ploid= # of SETS of chromosomes

Practice with Diploid and Haploid Chromosome Numbers of Common Organisms Organism Diploid Body Cell (2N) Haploid Gamete (1N) Fruit Fly 8 Garden Pea 14 Corn 20 Tomato 12 Leopard Frog 13 Apple 17 Human 46 Chimp 48 Dog 39 Fern 630 Organism Body Cell (2n) Gamete (n) Fruit fly 8 4 Garden pea 14 7 Corn 20 10 Tomato 24 12 Leopard Frog 26 13 Apple 34 17 Human 46 23 Chimpanzee 48 24 Dog 78 39 Adder’s tongue fern 1260 630

Vocabulary Sexual reproduction: When 2 haploid cells unite (fertilization) Zygote= fertilized egg =1st cell of offspring (Diploid)

Before Meiosis INTERPHASE Normal cell life and metabolism DNA is uncoiled chromatin. DNA is replicated (copied)! Why?

Starts with one diploid cell MEIOSIS Meiosis: cell division which produces 4 haploid gametes Starts with one diploid cell Ends with four haploid cells

Meiosis has two divisions Meiosis I 4 phases Meiosis II F:\OneDrive\Desktop\animations from bio powerpoints\Chapter 10 BDOL IC

Meiosis I Prophase I Nuclear envelope/nucleolus disappear Spindle apparatus forms. Chromosomes become visible (chromatin condenses) Homologous Chromosomes Pair up. Tetrad Crossing Over (Recombination) occurs the exchange of genetic material between homologous chromosomes.

Metaphase I Tetrads line up on the metaphase plate Alignment is random (Independent Assortment of Chromosomes)

Anaphase I Homologous Chromosomes separate and move to opposite poles

Telophase I Cytokinesis The cytoplasm divides Nuclear envelope re-forms Spindle breaks down Cytokinesis The cytoplasm divides Two new HAPLOID cells are created

Meiosis II Prophase II Nuclear envelope disappears Spindle apparatus forms and attaches to chromosomes

Metaphase II Chromosomes line up down metaphase plate (middle)

Anaphase II Sister chromatids separate and move toward opposite poles

Four haploid gametes have been formed!! Telophase II Nuclei reform Spindle breaks down Cytokinesis Cytoplasm divides Four haploid gametes have been formed!! C:\Documents and Settings\BBAUGHMAN\Desktop\bio powerpoints\Chapter 10 BDOL IC

Meiosis produces Diversity! How? Crossing over Independent Assortment Details…

Crossing-over Crossing over is the exchange of genetic material between homologous chromosomes. This increases the genetic variation in the gametes.

Independent Assortment The random distribution of chromosomes during meiosis. This independent assortment produces millions of possible gametes See picture…

Good Meiosis Video: http://www.mhhe.com/biosci/bio_animations/08_MH_Meiosis_Web/index.html

Nondisjunction Nondisjunction—the failure of homologous chromosomes or sister chromatids to separate during Meiosis Trisomy— an extra chromosome Ex. Down syndrome (trisomy 21) Monosomy- having one less chromosome Polyploidy= abnormal # of sets of chromosomes

Analyze the Karyotypes 1 2

Mitosis versus Meiosis 1. Mitosis produces diploid cells 2. Meiosis produces haploid cells 3. Mitosis produces two cells with the same genetic (DNA) material 4. Meiosis produces four cells with different genetic material.