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Reminder: Test Corrections due on MONDAY.

Reminder: Test Corrections due on MONDAY. Ch 13 Meiosis and Sexual Life Cycles. What do you know about chromosomes? Made of chromatin – DNA + protein 23 pairs (46 total) 22 autosomes + 1 sex chromosome XX - ♀ - female XY - ♂ - male What is the difference between haploid & diploid?

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Reminder: Test Corrections due on MONDAY.

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  1. Reminder: Test Corrections due on MONDAY.

  2. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • Made of chromatin – DNA + protein • 23 pairs (46 total) • 22 autosomes + 1 sex chromosome • XX - ♀ - female • XY - ♂ - male • What is the difference between haploid & diploid? • - haploid (n ) • - cells with 1 set of chromosomes • - gametes - sperm & egg • - diploid (2n) • - somatic cells • - 2 sets of chromosomes (1 set – mom & 1 set dad) • Meiosis creates haploid gametes that unite to produce a diploid zygote.

  3. Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3) Two sister chromatids of one replicated chromosome Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Figure 13.4 Describing chromosomes

  4. Ch 13 Meiosis and Sexual Life Cycles Key Haploid gametes (n = 23) Haploid (n) Ovum (n) Diploid (2n) Sperm Cell (n) FERTILIZATION MEIOSIS Diploid zygote (2n = 46) Ovary Testis Mitosis and development Multicellular diploid adults (2n = 46) • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • - testes • - ovaries

  5. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • What happens in meiosis? An overview. • Preceded by DNA replication • 2 consecutive cell divisions • meiosis I – separation of homologous chromosomes • meiosis II – separation of sister chromatids • Makes 4 unique daughter cells. Genetically different from • - each other • the parent cell

  6. Interphase Homologous pair of chromosomes in diploid parent cell Chromosomes replicate Homologous pair of replicated chromosomes Sister chromatids Diploid cell with replicated chromosomes Meiosis I 1 Homologous chromosomes separate Haploid cells with replicated chromosomes Meiosis II 2 Sister chromatids separate Haploid cells with unreplicated chromosomes Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number

  7. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • What happens in meiosis? An overview. • What happens during meiosis? The specifics.

  8. MEIOSIS I: Separates homologous chromosomes INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Sister chromatids remain attached Centromere (with kinetochore) Centrosomes (with centriole pairs) Chiasmata Metaphase plate Sister chromatids Spindle Nuclear envelope Homologous chromosomes separate Microtubule attached to kinetochore Tetrad Chromatin Tetrads line up Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example Pairs of homologous chromosomes split up Chromosomes duplicate Figure 13.8 The Meiotic Division of an Animal Cell • Prophase I (90% of meiosis) • Chromosomes condense • Centrosomes move apart • Nuclear envelope disappears Synapsis occurs forming tetrads Chromsomes line-up gene-by-gene Crossing over takes place at chiasmata

  9. MEIOSIS II: Separates sister chromatids TELOPHASE II AND CYTOKINESIS TELOPHASE I AND CYTOKINESIS METAPHASE II ANAPHASE II PROPHASE II Cleavage furrow Haploid daughter cells forming Sister chromatids separate Two haploid cells form; chromosomes are still double During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing single chromosomes Meiosis II – same as mitosis (separation of sister chromatids)

  10. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • What happens in meiosis? An overview. • What happens during meiosis? The specifics. • What are the differences between mitosis & meiosis? • Meiosis is a reduction division…mitosis cells have the same number of chromosomes. • Meiosis creates genetic variation…mitosis produces a clone. • Meiosis is 2 consecutive nuclear divisions….mitosis just 1.

  11. MITOSIS MEIOSIS Chiasma (site of crossing over) Parent cell (before chromosome replication) MEIOSIS I Prophase I Prophase Chromosome replication Chromosome replication Tetrad formed by synapsis of homologous chromosomes Duplicated chromosome (two sister chromatids) 2n = 6 Tetrads positioned at the metaphase plate Chromosomes positioned at the metaphase plate Metaphase I Metaphase Sister chromatids separate during anaphase Anaphase Telophase Homologues separate during anaphase I; sister chromatids remain together Anaphase I Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II Sister chromatids separate during anaphase II Figure 13.9 A comparison of mitosis and meiosis

  12. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • What happens in meiosis? An overview. • What happens during meiosis? The specifics. • What are the differences between mitosis & meiosis? • What are the 3 ways meiosis creates genetic variation? • Independent assortment of chromosomes (metaphase I) • Crossing over (prophase I) • Random fertilization

  13. Key Maternal set of chromosomes Possibility 1 Possibility 2 Paternal set of chromosomes Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 Combination 3 Combination 4 Figure 13.10 The independent assortment of homologous chromosomes in meiosis 223 possible combinations in humans

  14. Prophase I of meiosis Nonsister chromatids Tetrad Chiasma, site of crossing over Metaphase I Metaphase II Daughter cells Recombinant chromosomes Figure 13.11 The results of crossing over during meiosis • Prophase I • New chromosome combinations • non-sister chromatids are exchanged • 2 – 3 times per chromosome in humans

  15. Ch 13 Meiosis and Sexual Life Cycles • What do you know about chromosomes? • What is the difference between haploid & diploid? • Where does meiosis occur in us? • What happens in meiosis? An overview. • What happens during meiosis? The specifics. • What are the differences between mitosis & meiosis? • What are the 3 ways meiosis creates genetic variation? • Independent assortment of chromosomes (metaphase I) • Crossing over (prophase I) • Random fertilization • 223 = 8 million sperm • x • 223 = 8 million egg • 64 trillion unique combinations • Genetic variation contributes to evolution via natural selection

  16. Unit 1 FRQ Scores… • 0-14: You need to do something differently. • 16-22: These are “Level 2”-style answers. I’m not worried about students who scored within this range unless the trend continues. • 24-34: Solid score. Make your answers more precise to improve. • 36-50: Good job!

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