Meiosis and Sexual Life Cycles 10 Meiosis and Sexual Life Cycles

Inheritance of Genes __________________________________________ __________________________________________ 2

Sets of Chromosomes in Human Cells __________________________________________ __________________________________________ 3

duplicated chromosomes Figure 10.3 Application Technique Pair of homologous duplicated chromosomes 5 m Centromere Sister chromatids Figure 10.3 Research method: preparing a karyotype Metaphase chromosome 4

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Key Maternal set of chromosomes (n  3) 2n  6 Paternal set of Figure 10.4 Key Maternal set of chromosomes (n  3) 2n  6 Paternal set of chromosomes (n  3) Sister chromatids of one duplicated chromosome Centromere Figure 10.4 Describing chromosomes Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) 6

Animal Life Cycle multicelled body zygote diploid fertilization meiosis haploid gametes Fig. 10-8b, p.162

Key Haploid (n) n Gametes n Diploid (2n) n MEIOSIS FERTILIZATION Figure 10.6a Key Haploid (n) n Gametes n Diploid (2n) n MEIOSIS FERTILIZATION Zygote 2n 2n Figure 10.6a Three types of sexual life cycles (part 1: animal) Mitosis Diploid multicellular organism (a) Animals 8

(b) Plants and some algae Figure 10.6b Haploid multi- cellular organism (gametophyte) Key Haploid (n) Diploid (2n) Mitosis n Mitosis n n n n Spores Gametes MEIOSIS FERTILIZATION 2n Figure 10.6b Three types of sexual life cycles (part 2: plant) 2n Zygote Diploid multicellular organism (sporophyte) Mitosis (b) Plants and some algae 9

Haploid unicellular or multicellular organism Key Figure 10.6c Haploid unicellular or multicellular organism Key Haploid (n) Diploid (2n) Mitosis n Mitosis n n n Gametes n MEIOSIS FERTILIZATION Figure 10.6c Three types of sexual life cycles (part 3: fungi) 2n Zygote (c) Most fungi and some protists 10

Concept 10.3: Meiosis reduces the number of chromosome sets from diploid to haploid __________________________________________ __________________________________________ (that become gametes) 11

duplicated chromosomes Meiosis II Figure 10.7 Interphase Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Duplicated pair of homologous chromosomes Sister chromatids Diploid cell with duplicated chromosomes Meiosis I 1 Homologous chromosomes separate Figure 10.7 Overview of meiosis: how meiosis reduces chromosome number Haploid cells with duplicated chromosomes Meiosis II 2 Sister chromatids separate Haploid cells with unduplicated chromosomes 12

Interphase Pair of homologous chromosomes in diploid parent cell Figure 10.7a Interphase Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Duplicated pair of homologous chromosomes Figure 10.7a Overview of meiosis: how meiosis reduces chromosome number (part 1: interphase) Sister chromatids Diploid cell with duplicated chromosomes 13

duplicated chromosomes Meiosis II 2 Sister chromatids separate Figure 10.7b Meiosis I 1 Homologous chromosomes separate Haploid cells with duplicated chromosomes Meiosis II 2 Sister chromatids separate Figure 10.7b Overview of meiosis: how meiosis reduces chromosome number (part 2: meiosis I and II) Haploid cells with unduplicated chromosomes 14

__________________________________________ NOTE – this is not part of the text, but rather a quick summary of what is in Figure 10.8. Animation: Meiosis Video: Meiosis I in Sperm Formation 15

MEIOSIS I: Separates homologous chromosomes Figure 10.8a MEIOSIS I: Separates homologous chromosomes Telophase I and Cytokinesis Prophase I Metaphase I Anaphase I Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole pair) Cleavage furrow Chiasmata Metaphase plate Spindle Figure 10.8a Exploring meiosis in an animal cell (part 1: meiosis I) Homologous chromosomes separate Fragments of nuclear envelope Microtubule attached to kinetochore Homologous chromosomes 16

MEIOSIS II: Separates sister chromatids Figure 10.8b MEIOSIS II: Separates sister chromatids Telophase II and Cytokinesis Prophase II Metaphase II Anaphase II Sister chromatids separate Figure 10.8b Exploring meiosis in an animal cell (part 2: meiosis II) Haploid daughter cells forming 17

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Daughter cells of meiosis II Figure 10.9a MITOSIS MEIOSIS Parent cell Chiasma MEIOSIS I Prophase Prophase I Chromosome duplication Chromosome duplication Homologous chromosome pair Duplicated chromosome 2n = 6 Individual chromosomes line up. Pairs of chromosomes line up. Metaphase Metaphase I Anaphase Sister chromatids separate. Homologs separate. Anaphase I Telophase Telophase I Figure 10.9a A comparison of mitosis and meiosis in diploid cells (part 1: mitosis vs. meiosis art) Sister chromatids separate. Daughter cells of meiosis I 2n 2n MEIOSIS II Daughter cells of mitosis n n n n Daughter cells of meiosis II 21

Chromosome duplication Chromosome duplication Figure 10.9aa MITOSIS MEIOSIS MEIOSIS I Parent cell Prophase Chiasma Prophase I Homologous chromosome pair Duplicated chromosome Chromosome duplication Chromosome duplication 2n = 6 Individual chromosomes line up. Pairs of chromosomes line up. Figure 10.9aa A comparison of mitosis and meiosis in diploid cells (part 1a: prophase and metaphase art) Metaphase I Metaphase 22

Daughter cells of mitosis Figure 10.9ab MITOSIS MEIOSIS Anaphase Anaphase I Telophase Telophase I Sister chromatids separate. Homologs separate. Sister chromatids separate. Daughter cells of meiosis I MEIOSIS II 2n 2n n n Figure 10.9ab A comparison of mitosis and meiosis in diploid cells (part 1b: anaphase, telophase and meiosis II art) Daughter cells of mitosis n n Daughter cells of meiosis II 23

SUMMARY Property Mitosis Meiosis DNA replication Figure 10.9b SUMMARY Property Mitosis Meiosis DNA replication Occurs during interphase before mitosis begins Occurs during interphase before meiosis I begins Number of divisions One, including prophase, prometaphase, metaphase, anaphase, and telophase Two, each including prophase, metaphase, anaphase, and telophase Synapsis of homologous chromosomes Does not occur Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Number of daughter cells and genetic composition Two, each diploid (2n) and genetically identical to the parent cell Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Figure 10.9b A comparison of mitosis and meiosis in diploid cells (part 2: mitosis vs. meiosis table) Role in the animal body Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Produces gametes; reduces number of chromosome sets by half and introduces genetic variability among the gametes 24

Concept 10.4: Genetic variation produced in sexual life cycles contributes to evolution __________________________________________ 25

Origins of Genetic Variation Among Offspring __________________________________________ __________________________________________ ___________________________________ 26

Possible Chromosome Combinations ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________

Possible Chromosome Combinations ___________________________________ ___________________________________ ___________________________________

Possibility 2 Possibility 1 Two equally probable arrangements of Figure 10.10-1 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Figure 10.10-1 The independent assortment of homologous chromosomes in meiosis (step 1) 29

Possibility 2 Possibility 1 Two equally probable arrangements of Figure 10.10-2 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 10.10-2 The independent assortment of homologous chromosomes in meiosis (step 2) 30

Possibility 1 Possibility 2 Two equally probable arrangements of Figure 10.10-3 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Figure 10.10-3 The independent assortment of homologous chromosomes in meiosis (step 3) Daughter cells Combination 1 Combination 2 Combination 3 Combination 4 31

combinations possible Possible Chromosome Combinations 1 2 3 combinations possible or or or Fig. 10-7, p.161

Crossing over Prophase I of meiosis Nonsister chromatids held together Figure 10.11-1 Prophase I of meiosis Nonsister chromatids held together during synapsis Pair of homologs Crossing over Figure 10.11-1 The results of crossing over during meiosis (step 1) 33

Crossing over Prophase I of meiosis Nonsister chromatids held together Figure 10.11-2 Prophase I of meiosis Nonsister chromatids held together during synapsis Crossing over Pair of homologs Synapsis and crossing over Chiasma Centromere TEM Figure 10.11-2 The results of crossing over during meiosis (step 2) 34

Crossing over Prophase I of meiosis Nonsister chromatids held together Figure 10.11-3 Prophase I of meiosis Nonsister chromatids held together during synapsis Crossing over Pair of homologs Synapsis and crossing over Chiasma Centromere TEM Breakdown of proteins holding sister chromatid arms together Anaphase I Figure 10.11-3 The results of crossing over during meiosis (step 3) 35

Crossing over Prophase I of meiosis Nonsister chromatids held together Figure 10.11-4 Prophase I of meiosis Nonsister chromatids held together during synapsis Crossing over Pair of homologs Synapsis and crossing over Chiasma Centromere TEM Breakdown of proteins holding sister chromatid arms together Anaphase I Figure 10.11-4 The results of crossing over during meiosis (step 4) Anaphase II 36

Crossing over Prophase I of meiosis Nonsister chromatids held together Figure 10.11-5 Prophase I of meiosis Nonsister chromatids held together during synapsis Crossing over Pair of homologs Synapsis and crossing over Chiasma Centromere TEM Breakdown of proteins holding sister chromatid arms together Anaphase I Figure 10.11-5 The results of crossing over during meiosis (step 5) Anaphase II Daughter cells Recombinant chromosomes 37

Random Fertilization ___________________________________ ___________________________________ ___________________________________ (from independent assortment) ___________________________________ ___________________________________ 38