Cell Division - Meiosis

I. Who Does Meiosis and Why? A. Who: All Multicellular Eukaryotes Animals, Plants, Fungi, some algae B. Why: Meiosis is needed for sexual reproduction C. Why do Sexual Reproduction ? 1. It allows genetic recombination 2.New combinations of genes may .. a. better suit environments b. allow offspring to survive radical environmental change c. allow offspring to survive a disease outbreak

II. Vocab A. Cells produced by meiosis = Gametes B. Sex Chromosomes = determine sex (in humans XX = female, Xy = male) C. Autosomes = any chromosome not used to determine sex of offspring

. D. Gametes = haploid cells made by meiosis E. Haploid cells have 1 set of chromosomes….. (1 of each kind) 1. called 1n cells 2. mathematical representation 3. n = number of different C types

Example: Humans have 23 different types 22 autosomes + 1 sex determining Gametes would have 1 of each kind So the 1n number for humans is… 23 (1*n) = (1*23)

. F. Diploid cells have 2 of each kind of chromosome G. 2n cells are diploid cells Example: Humans = 23 types Diploid cells have 2 of each type -> 2n Chromosome number = 46 (2*23)= (2*n)

Based on the Cat Karyotype below, calculate the 1n and 2n number for cats 18 different autosomes (C # 1-18) one pair of sex chromosomes So 19 different kinds 1n = 1(19) = 19 2n = 2(19) = 38

III. How/Where Haploid Cells are produced A. Where: Animals: Meiosis only in gonads 1. Gonads = reproductive organs a. testis b. ovary 2. Specialized cells in gonad do meiosis a. spermatocytes b. oocytes 3. Spermatocytes and oocytes are constantly replaced by specialized Spermatogonia cells & oogonia cells

IV. Spermatogenesis A. Spermatogonia cells do Mitosis make 1. a 1◦ spermatocyte 2. a cell that stays a spermatogonia B. The 1◦ spermatocyte does meiosis to make 4 spermatids

C. Spermatids differentiate into sperm 1. Acrosome = vesicle w/ penetrating enzymes 2. Nucleus = 1n 3. Midpiece makes ATP & powers flagellum 4. Tail = flagellum

V. Oogenesis Oogonia do Mitosis to make 1 primary Oocyte Which does… Meiosis I to make 1 secondary oocyte and one polar body Meiosis II makes 1 ovum &1 polar body

Meiosis I:separate homologous pairs (cells become 1n with X shape C) Prophase I : same as mitosis + Synapsis & crossing over Metaphase I : C line up in pairs

. Anaphase I : Homologs move to opposite poles (cohesin along arms breaks down) (cohesin at centromeres remains)

Telophase I : Cytokinesis simultaneously X shaped C reach poles Many cells do not decondense C or reform nuclear E Spindle only partly broken down

Homologous Chromosomes Homologous Chromosomes are same C type same length code for same genes (but can be different versions) Unless they are X and y which are the only pair of Homologues that do not look alike

Synapsis Homologous Chromosomes pair up Line up gene to gene then physically connect along their arms Proteins form a synaptonemal complex that bind them together

. Crossing Over : Non-sister chromosomes trade corresponding segments of DNA Genes far from centromere cross over most often Location of a gene on a chromosome = the gene’s locus (loci) Distance from centromere measured in map units

Chiasmata X shaped region where crossing over has happened. Synaptonemal complex has broken down but … Cohesions still hold sister chromatids together

Meiosis in Fungi Fungal bodies formed of hyphae Filaments made of chains of 1n cells Hyphae interweave to form fungus body The body mass is called a mycelium

Phylum Ascomycota don’t make mushrooms Hypha can be + or – If one of each meet then… 2 cells (one + one-) fuse cytoplasm (plasmogamy) Then fuse their nuclei … now 2n (karyogamy) Then do meiosis…making 4 haploid nuclei

Each 1n nucleus does mitosis So now 8 nuclei in the cell Each nucleus grows a tough casing around it and becomes a Spore (ascospore) Spores disperse on wind Germinate to make new 1n hyphae .

The ascospores that form from one cell stay together in a capsule called an ascus

Perithecia = ascocarp

Homologous C both have gene for spore color…one tan color one black color No crossing over = 4:4 Any other pattern results from crossing over

Genetic Variation Increased by crossing over Increased by Independent Assortment.. Each pair of homologues lines up randomly and Independent of how other pairs line up # different gametes formed = 2n Humans = 223 or 8,399,608