Meiosis Where Babies come from….

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Same story but different versions Copies of those versions that are identical to their original

Code for the same genes but different versions Copies of those versions that are identical to their original Homologous Chromosomes Sister Chromatids

There are two types of chromosomes found in cells: - autosomes - sex chromosomes Your body cells have 23 pairs of chromosomes - homologous pairs of chromosomes have the same structure - for each homologous pair, one chromosome comes from each parent Chromosome pairs 1-22 are autosomes. Sex chromosomes, X and Y, determine gender in mammals. XX = XY = female male Bio NOTES: Chromosomes and Meiosis

HOMOLOGOUS CHROMOSOMES Image modified by Riedell SAME SIZE SAME SHAPE CARRY GENES for the SAME TRAITS BUT ______________! (Don’t have to have the SAME CHOICES) NOT IDENTICAL

Body Cells - also called somatic cells - body cells are diploid Diploid (2n) cells – have two copies of every chromosome - half the chromosomes come from each parent Gametes - also known as sex cells (sperm and egg) - gametes have DNA that can be passed to offspring - gametes are haploid Haploid (n) cells – have one copy of each chromosome - gametes have 22 autosomes and 1 sex chromosome

Key Terms Diploid refers to complete chromosome sets in a cell (or 2N) –N= the number of chromosomes in a gamete (sex cell) – N chromosomes from the female parent + N chromosomes from the male parent= 2N –For humans, 2N = 46

Key Terms Haploid refers to single chromosomes in a cell (or N) –One-half of the 2N set (the maternal N or the paternal N) –Gametes (i.e. sperm, egg sex cells) are haploid cells –For humans, N = 23

Bottom Line diploid means there are the full number of chromosomes in cells haploid means that there are half the number of chromosomes in cells

Mitosis and meiosis are types of nuclear division that make different types of cells. Mitosis - occurs in somatic cells -makes 2 diploid cells -Produces somatic cells that are genetically Identical Meiosis - occurs in sex cells (gametes) -makes 4 haploid cells - produces gametes that are genetically Unique

MEIOSIS 10-1 Making gametes…

EGG + SPERM  If egg and sperm had same number of chromosomes as other body cells... baby would have too many chromosomes! Image by Riedell

MEIOSIS is the way… to make cells with ½ the number of chromosomes for sexual reproduction

Cells go through two rounds of division in meiosis: Meiosis reduces the chromosome number and creates genetic diversity. homologous chromosomes sister chromatids sister chromatids Meiosis I and meiosis II each have four phases, similar to those in mitosis During meiosis I – pairs of homologous chromosomes separate - homologous chromosomes are similar, but not identical During meiosis II – sister chromatids divide - sister chromatids are copies of the same chromosome

Meiosis I Meiosis I occurs after DNA has been replicated in interphase Meiosis I divides homologous chromosomes in four phases: prophase I  metaphase I  anaphase I  telophase I After cytokinesis, two cells are produced with one homologous chromosome each

Meiosis II Meiosis II divides sister chromatids in four phases: prophase II  metaphase II  anaphase II  telophase II DNA is not replicated between meiois I and meiosis II After cytokinesis, four new cells are produced, each with half the chromosome number (haploid)

Stop here day 1 Option 1 Work on Vocab List Option 2 Complete Web quest

MITOSISMITOSIS vs MEIOSIS INTERPHASE INTERPHASE IMEIOSIS DNA is spread out as chromatin Nuclear membrane/ nucleolus visible DNA is copied during S phase Makes stuff new cell needs in G 2 SAME AS MITOSIS

MITOSIS vs MEIOSIS PROPHASE PROPHASE I DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/spindle fibers appear DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/spindle fibers appear Homologous pairs match up CROSSING OVER OCCURS!

WHAT MAKES MEIOSIS DIFFERENT? 1. Exchange of DNA between homologous pairs = _____________ during PROPHASE I CROSSING OVER Allows shuffling of genetic material

Video 5 Click the image to play the video segment. 11E Video 5 Crossing Over SEE CROSSING OVER ANIMATION

CROSSING OVER Image modified by Riedell Allows for_________________ in different combinations After crossing over, chromatid arms are________________ anymore rearranging of DNA NOT IDENTICAL

MITOSIS vs MEIOSIS METAPHASE METAPHASE I Chromosomes line up in middle HOMOLOGOUS Chromosomes line up in middle Independent assortment occurs

METAPHASE I Spindle fibers attach to the centromeres Homologous Chromosomes Line up at the equator chromosome pairs line up randomly in cell

Video 4 Click the image to play the video segment 11D. Video 4 Segregation of Chromosomes

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE I APART: Chromatids split APART: Chromatids stay together Homologous pairs split

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE I See TWO nuclei Nuclear membrane/ nucleolus return DNA spreads out as chromatin Spindle/centrioles disappear SAME

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS I Cytoplasm splits into 2 cells SAME AS MITOSIS 2 Genetically Different Haploid Cells Form

MITOSIS vs MEIOSIS INTERPHASE II DNA is spread out as chromatin Nuclear membrane/ nucleolus visible DNA is copied during S phase SKIP INTERPHASE II DNA NOT COPIED

MITOSIS vs MEIOSIS PROPHASE PROPHASE II DNA scrunches into chromosomes Nuclear membrane/ nucleolus disappear Centrioles/ spindle fibers appear SAME AS MITOSIS

MITOSIS vs MEIOSIS METAPHASE METAPHASE II Chromosomes line up in middle SAME AS MITOSIS

MITOSIS vs MEIOSIS ANAPHASE ANAPHASE II Sister Chromatids split and move apart SAME AS MITOSIS

MITOSIS vs MEIOSIS TELOPHASE TELOPHASE II Two nuclei Nuclear membrane/ nucleolus returns Centrioles/spindle fibers disappear DNA spreads out as chromatin Same as Mitosis

MITOSIS vs MEIOSIS CYTOKINESIS CYTOKINESIS II Cytoplasm splits 2 diploid Genetically Identical cells SAME AS MITOSIS 4 haploid Genetically unique Cells

Stop Here day 2 Complete Vocab and SG sheet due by end of class.

Ways Meiosis is different? Homologous pairs match up & trade DNA (&CROSSING OVER) in PROPHASE I INDEPENDENT ASSORTMENT in metaphase I creates genetic recombination Skipping INTERPHASE II- (Dividing TWICE but copying DNA once) produces 1n cells

Sources of Variations and Differences Crossing over Random assortment of chromosomes Fertilization occurs during prophase I homologous chromosomes swap pieces this chromosome swapping creates variations chromosome pairs line up randomly in cell when the pairs separate, this creates cells with genetic variations which sperm gets to the egg first?? it is random and can create variations in offspring