Do Now Take out 10.2 vocabulary homework Complete handout Remember haploid = half Diploid = double So if 20 is the diploid number, then 10 is the haploid number. If 5 is the haploid number, then 10 is the diploid number HOMEWORK: STUDY FOR YOUR MIDTERM!

Meiosis: Making haploid reproductive cells

Goal of Meiosis The purpose is to make haploid cells so that when 2 haploid cells combine you have a new diploid offspring that has an original combination of genes. + = Haploid cell + Haploid cell = Diploid cell (2n) (1n) (1n) that turns into a muticellular offspring

Meiosis Overview The Goal: Makes 4 haploid cells Takes place in sex cells (gametes) such as egg & sperm cells Location: Testes (male) and ovaries (female) The Goal: To make 4 haploid daughter cells for reproduction that are genetically different from the parent cells. Each haploid daughter cell will contain a mixture of the parents chromosomes, so that the 4 daughter cells should be different.

Meiosis Involves 2 cell divisions The cell will go through interphase (G1, S, G2)…but then will divide twice  resulting in 4 haploid cells There are 2 parts in Meiosis: Meiosis 1 Meiosis 2

Meiosis I and Meiosis II Both go through each of the phases of mitosis (PMAT) After each one cytokinesis occurs The goal is to reduce chromosome number to haploid so that 2 cells can combine to make a diploid organism

Meiosis 1: Prophase 1 DNA coils into chromatids Spindle fibers appear Nucleus/nucleolus disappear *Homologous chromosomes pair up into tetrads of 4 chromatids, called synapsis *Crossing over may occur causing genetic recombination

What is crossing over? When a homologous pair bumps into each other during prophase I and they exchange portions one chromatid  leads to genetic recombination

Metaphase I & Anaphase I Tetrads line up randomly in the center. Spindle fibers attach to each end of the homologous pair Anaphase I: Homologous pairs split randomly

Independent Assortment The random lining up of homologous pairs during metaphase I. This allows for different gametes to be possible and also leads toward genetic recombination

More independent assortment

What is genetic recombination? …when the combination of genes in an offspring are different from the gene combination found in the parents Occurs in 2 ways in meiosis 1. Crossing over where homologous pairs exchange portions of one chromatid 2. Independent assortment where the homologous pairs line up randomly or without influences like which parent they came from or whether they are dominant or recessive.

Telophase I and Cytokinesis I Chromosomes reach poles Cytokinesis occurs forming 2 new cells. Nuclear membrane may or may not reform before meiosis II

Meiosis II (2nd cell division, similar to mitosis steps, PMAT) Prophase II: Spindle fibers form Metaphase II: Chromosomes move to center (along equator) Anaphase II: Chromatids separate toward the poles Telophase II: Nuclear membrane reforms. Spindle fibers disassemble. Cytokinesis occurs forming 4 haploid cells with 1 copy of each chromosome.

Do Now – complete on a blank piece of paper with the date and place in your do now section 1. Where does Meiosis take place in the body? Sex cells 2. What kind of cells does Meiosis produce? Haploid 3. What are the two ways that Meiosis causes genetic recombination? Crossing over and independent assortment Homework: Meiosis handout

How does Meiosis differ in males vs. females? Since meiosis is producing sex cells (sperm & eggs) it takes place in the testes (males) & the ovaries (female) In males: Spermatogenesis - the formation of 4 spermatids (haploid cells) which will turn into spermatozoa (sperm cells). In females: Oogenesis - the formation of 1 egg cell (ova) with more cytoplasm than the other 3 cells. The remaining 3 cells are called polar bodies and will disintegrate

The phases of Meiosis

Diagrams

Let us compare Mitosis VS. Meiosis Mitosis makes IDENTICAL cells to the parent Mitosis make DIPLOID cells Mitosis occurs in BODY cells Mitosis makes 2 DAUGHTER CELLS Meiosis make DIFFERENT cells from the parent Meiosis makes HAPLOID cells Meiosis occurs in REPRODUCTIVE cells Meiosis makes 4 DAUGHTER CELLS

Meiosis square dance Take a set of lyrics AND Get ready to sing 

Animations Johnkyrk.com http://www.lewport.wnyric.org/jwanamaker/animations/meiosis.html http://www.stolaf.edu/people/giannini/ Meiosis square dance