The cell division of love (and diversity) <3 Meiosis The cell division of love (and diversity) <3 EQ: How does the sorting and recombination of genes in meiosis result in a greater genetic variation?

Meiosis Chromosomes Duplicated Homologous chromosome made of 2 sister chromatids held together at centromere Each chromatid contain identical copies of DNA Each Chromosome may contain different variations Homologous duplicated chromosomes homologous chromosomes Homo = same THIS IS MEIOSIS Logos = word or plan single-stranded sister chromatids double-stranded

Homologous Chromosomes vs. Sister Chromatids Homologous Chromosomes: two duplicated chromosomes containing the same genes (eye color/hair color) Could contain different variations of the same genes. Divided during meiosis I Sister Chromatids: one half of the duplicated chromosome Sister chromstids contain the exact same copy of genes The duplicated sides of the chromosome that remain attached at the centromere Divided during meiosis II sister chromatids sister chromatids

Chromosomes Autosomes: chromosomes that contain genes for characteristics NOT related to the sex of an organism Chromosome pairs 1-22 in humans Sex Chromosomes: directly control the development of sexual characteristics Pair 23 – in mammals, the X and Y chromosomes determine gender Female = X X Male = X Y

Sex Chromosomes The X chromosome The Y chromosome larger sex chromosome contains genes that have nothing to do with sexual characteristics The Y chromosome the smallest chromosome The genes on this chromosome direct the development of testes and other male traits

Types of Cells Somatic Cells: Gametes: body cells Diploid – Contains two copies of chromosomes (46) Produced by Mitosis Ex. skin cells, liver cells Gametes: sex cells Haploid- Contain half the number of chromosomes (23) Produced by Meiosis Ex. eggs (female) and sperm (male)

Gametes (Sex Cells) - 23 Somatic Cells (Body Cells)- 46

Sexual Reproduction: Sexual reproduction- process by which two gametes fuse during fertilization and the offspring are a genetic mixture of both parents Benefits: Allows genetic variation in offspring- differences in appearances that offspring show from their parents. Allows for the ability to adapt to environmental changes

What must happen before a cell can divide? INTERPHASE!!!! DNA must Duplicate!

Gametes are haploids, Which means? Sex cells have half the chromosomes as somatic cells. Think/Pair/Share How do you think they get to have half the number of chromosomes?

Steps of Meiosis Interphase I Meiosis I Prophase I : Crossing Over G1, S, G2 (Cell growth and DNA rep) Meiosis I Prophase I : Crossing Over Metaphase I: Independent assortment Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II Students are not writing this page down.

Meiosis 1 Main points: Interphase occurs = DNA replication Crossing over occurs = exchange of genetic material Homologous chromosomes separate Results in 2 diploid daughter cells

Prophase I Homologous chromosomes pair up nuclear membrane breaks down Centrioles move apart crossing over can occur

Crossing Over exchange of chromosomes segments during prophase I Create new combinations during prophase I sister chromatids intertwine and swap pieces of chromosome Skip to bottom on notes

Metaphase I homologous chromosomes align along the middle of the cell each side has a chromosome from each parent Independent assortment occurs Random alignment of homologous chromosomes (genetic variation)

Anaphase I the paired homologous chromosomes split and move towards centrioles at opposite poles sister chromatids are still attached

Telophase I spindle fibers fall apart nuclear membrane reforms around chromosomes 2 nuclei

Cytokinesis Cytoplasm divides two diploid cells are produced How many chromosomes are in a diploid cell? 46

The value of meiosis 1 Consistency over time keeps chromosome number same from generation to generation Mom from Mom Consider the greater variation with 23 pairs of chromosomes = mixing and matching Dad offspring from Dad

Meiosis II Main Points: No interphase = no DNA replication Sister chromatids separate Results in 4 genetically different, haploid gametes (n)

Prophase II centrioles move to opposites sides nuclear envelope breaks down

Metaphase II spindle fibers align sister chromotids along the metaphase plate (middle)

Anaphase II sister chromatids are pulled apart towards opposite sides of the cell by centrioles

Telophase II spindle fibers fall apart nuclear membrane forms

Cytokinesis Cytoplasm divides Produces 4 haploid gametes Each gamete is genetically unique

new gametes made by offspring The value of Meiosis II Change over time introduces genetic variation No two gametes are the same new gametes made by offspring Consider the greater variation with 23 pairs of chromosomes = mixing and matching from Dad variation from Mom offspring

Results – reduction division 1 diploid divides into FOUR HAPLOID DAUGHTER (gametes) Reduces the number of chromosomes to 23 Each gamete is unique from one another (and parent) Female gametes are eggs and male gametes are sperm

Stop and think How does the process if meiosis produce haploid cells instead of diploid? There is only one round in interphase and two rounds of division Why is it important that the gametes produced in meiosis are haploid and not diploid? During fertilization the zygote has the correct number of chromosomes Why is meiosis called reduction division?

Putting it all together… meiosis  fertilization  mitosis + development gametes 46 23 46 23 46 46 46 46 46 23 meiosis 46 46 egg 46 46 23 zygote fertilization mitosis & development mitosis sperm

The whole Process

LAB REVIEW What is a centriole? What is a centromere? Where are they located? What is a centromere? What is divided in Meiosis 1? What is divided in Meiosis 2? What materials represent: Chromosomes Centrioles Centromeres Nucleus Cell Spindle fibers

Meiosis Gummy Worm Lab C: Level 2 voice H: Work with table group (Raise hand for help) A: Meiosis lab and answer the analysis questions M: Remain seated at assigned table P: complete own sheet and paste into your notebook Success!

Exit ticket Clear desk of everything except DO NOW and something to write with