Ch 13 Meiosis and Sexual Life Cycles Test Corrections – Ch 9 – 12 Due on Friday

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? -Made of chromatin – DNA + protein -23 pairs (46 total) -22 autosomes + 1 sex chromosome -XX - ♀ - female -XY - ♂ - male 2.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.

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

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? - testes - ovaries Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) Ovum (n) Sperm Cell (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi Diploid multicellular organism Key MEIOSIS FERTILIZATION MEIOSIS FERTILIZATION MEIOSIS FERTILIZATION n n n n n n n n n n n n n 2n Zygote Gametes Haploid multicellular organism (gametophyte) Haploid multicellular organism Haploid Diploid Mitosis Spores Gametes Mitosis Gametes Mitosis Zygote Mitosis (a) Animals Diploid multicellular organism (sporophyte) (b) Plants and some algae (c) Most fungi and some protists

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi. 5.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

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

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi. 5.What happens in meiosis? An overview. 6.What happens during meiosis? The specifics.

Centrosomes (with centriole pairs) Sister chromatids Chiasmata Spindle Tetrad Nuclear envelope Chromatin Centromere (with kinetochore) Microtubule attached to kinetochore Tetrads line up Metaphase plate Homologous chromosomes separate Sister chromatids remain attached Pairs of homologous chromosomes split up Chromosomes duplicate Homologous chromosomes (red and blue) pair and exchange segments; 2n = 6 in this example INTERPHASE MEIOSIS I: Separates homologous chromosomes PROPHASE I METAPHASE I ANAPHASE I 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

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

Test corrections (if done) - Staple behind the test - Tuck scantron inside test - Place in box Can transport – Wednesday – all day & 4:30 loading

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi. 5.What happens in meiosis? An overview. 6.What happens during meiosis? The specifics. 7.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.

MITOSIS MEIOSIS Prophase Duplicated chromosome (two sister chromatids) Chromosome replication Chromosome replication Parent cell (before chromosome replication) Chiasma (site of crossing over) MEIOSIS I Prophase I Tetrad formed by synapsis of homologous chromosomes Metaphase Chromosomes positioned at the metaphase plate Tetrads positioned at the metaphase plate Metaphase I Anaphase I Telophase I Haploid n = 3 MEIOSIS II Daughter cells of meiosis I Homologues separate during anaphase I; sister chromatids remain together Daughter cells of meiosis II n n nn Sister chromatids separate during anaphase II Anaphase Telophase Sister chromatids separate during anaphase 2n2n2n2n Daughter cells of mitosis 2n = 6 Figure 13.9 A comparison of mitosis and meiosis

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi. 5.What happens in meiosis? An overview. 6.What happens during meiosis? The specifics. 7.What are the differences between mitosis & meiosis? 8.What are the 3 ways meiosis creates genetic variation? -Independent assortment of chromosomes (metaphase I) -Crossing over (prophase I) -Random fertilization

Key Maternal set of chromosomes Paternal set of chromosomes Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Possibility 2 Metaphase II Daughter cells Combination 1 Combination 2Combination 3Combination 4 Figure The independent assortment of homologous chromosomes in meiosis 2 23 possible combinations in humans

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

Ch 13 Meiosis and Sexual Life Cycles 1.What do you know about chromosomes? 2.What is the difference between haploid & diploid? 3.Where does meiosis occur in us? 4.Let’s check out meiosis in other organisms…plants & fungi. 5.What happens in meiosis? An overview. 6.What happens during meiosis? The specifics. 7.What are the differences between mitosis & meiosis? 8.What are the 3 ways meiosis creates genetic variation? -Independent assortment of chromosomes (metaphase I) -Crossing over (prophase I) -Random fertilization = 8 million sperm x = 8 million egg -64 trillion unique combinations -Genetic variation contributes to evolution via natural selection