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CAMPBELL BIOLOGY IN FOCUS Urry • Cain • Wasserman • Minorsky • Jackson • Reece 10 Meiosis and Sexual Life Cycles Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge © 2014 Pearson Education, Inc. Inheritance of Genes Each gene has a specific locus, on a certain chromosome © 2014 Pearson Education, Inc. Sets of Chromosomes in Human Cells A karyotype is an ordered display of the pairs of chromosomes from a cell The 2 in each pair are called homologous chromosomes, or homologs These carry genes controlling the same inherited characters – 1 from each parent © 2014 Pearson Education, Inc. Figure 10.3 Application Technique Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome © 2014 Pearson Education, Inc. 5 m The sex chromosomes are called X and Y remaining 22 pairs are called autosomes © 2014 Pearson Education, Inc. Figure 10.4 Key 2n 6 Maternal set of chromosomes (n 3) Paternal set of chromosomes (n 3) Sister chromatids of one duplicated chromosome Two nonsister chromatids in a homologous pair © 2014 Pearson Education, Inc. Centromere Pair of homologous chromosomes (one from each set) Animal Life Cycle multicelled body zygote fertilization diploid haploid meiosis gametes © 2014 Pearson Education, Inc. Fig. 10-8b, p.162 Figure 10.6a Key n Gametes n n MEIOSIS 2n Diploid multicellular organism (a) Animals © 2014 Pearson Education, Inc. FERTILIZATION Zygote 2n Mitosis Haploid (n) Diploid (2n) Figure 10.6b Haploid multicellular organism (gametophyte) Mitosis n Key Haploid (n) Diploid (2n) Mitosis n n Spores MEIOSIS 2n Diploid multicellular organism (sporophyte) Gametes FERTILIZATION 2n Mitosis (b) Plants and some algae © 2014 Pearson Education, Inc. n n Zygote Figure 10.6c Haploid unicellular or multicellular organism Mitosis Key Haploid (n) Diploid (2n) Mitosis n n n n Gametes FERTILIZATION MEIOSIS 2n Zygote (c) Most fungi and some protists © 2014 Pearson Education, Inc. n Concept 10.3: Meiosis reduces the number of chromosome sets from diploid to haploid Meiosis 2 sets of cell divisions…meiosis I and meiosis II results in 4 haploid daughter cells (that become gametes) © 2014 Pearson Education, Inc. 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 Meiosis II Haploid cells with duplicated chromosomes 2 Sister chromatids separate Haploid cells with unduplicated chromosomes © 2014 Pearson Education, Inc. Figure 10.7a Interphase Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes Sister chromatids © 2014 Pearson Education, Inc. Chromosomes duplicate Diploid cell with duplicated chromosomes Figure 10.7b Meiosis I 1 Homologous chromosomes separate Meiosis II Haploid cells with duplicated chromosomes 2 Sister chromatids separate Haploid cells with unduplicated chromosomes © 2014 Pearson Education, Inc. Meiosis I, homologous pairs pair and separate Meiosis II, sister chromatids separate Animation: Meiosis Video: Meiosis I in Sperm Formation © 2014 Pearson Education, Inc. Figure 10.8a MEIOSIS I: Separates homologous chromosomes Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole Cleavage pair) furrow Chiasmata Metaphase Spindle plate Fragments of nuclear envelope Homologous chromosomes © 2014 Pearson Education, Inc. Homologous chromosomes separate Microtubule attached to kinetochore Figure 10.8b MEIOSIS II: Separates sister chromatids Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming © 2014 Pearson Education, Inc. In synapsis, homologous chromosomes loosely pair up, aligned gene by gene © 2014 Pearson Education, Inc. In crossing over, nonsister chromatids exchange DNA segments Crossing over produces recombinant chromosomes, which combine DNA from each parent © 2014 Pearson Education, Inc. 3 events unique to meiosis, all in meiosis l Synapsis and crossing over Homologous pairs at the metaphase plate: Separation of homologs © 2014 Pearson Education, Inc. Figure 10.9a MITOSIS MEIOSIS Parent cell Chiasma MEIOSIS I Prophase I Prophase Duplicated chromosome Metaphase Anaphase Telophase 2n Daughter cells of mitosis © 2014 Pearson Education, Inc. Chromosome duplication 2n = 6 Chromosome duplication Individual chromosomes line up. Pairs of chromosomes line up. Sister chromatids separate. Homologs separate. 2n Sister chromatids separate. Homologous chromosome pair Metaphase I Anaphase I Telophase I Daughter cells of meiosis I MEIOSIS II n n n n Daughter cells of meiosis II Figure 10.9aa MITOSIS Prophase Duplicated chromosome MEIOSIS Parent cell Chromosome Chromosome duplication 2n = 6 duplication Individual chromosomes line up. Metaphase © 2014 Pearson Education, Inc. Chiasma Pairs of chromosomes line up. MEIOSIS I Prophase I Homologous chromosome pair Metaphase I Figure 10.9ab MEIOSIS MITOSIS Anaphase Telophase Sister chromatids separate. 2n Daughter cells of mitosis © 2014 Pearson Education, Inc. 2n Anaphase I Telophase I Homologs separate. Sister chromatids separate. Daughter cells of meiosis I MEIOSIS II n n n n Daughter cells of meiosis II 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 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 © 2014 Pearson Education, Inc. Concept 10.4: Genetic variation produced in sexual life cycles contributes to evolution Mutations …the original source of genetic diversity Mutations create different alleles Reshuffling alleles produces genetic variation © 2014 Pearson Education, Inc. Origins of Genetic Variation Among Offspring meiotic mechanisms that contribute to genetic variation Independent assortment of chromosomes Crossing over Random fertilization © 2014 Pearson Education, Inc. Possible Chromosome Combinations As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n (and this is without crossing over) © 2014 Pearson Education, Inc. Possible Chromosome Combinations 2n for humans would be … 223 or… 8,388,608 © 2014 Pearson Education, Inc. Figure 10.10-1 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I © 2014 Pearson Education, Inc. Figure 10.10-2 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II © 2014 Pearson Education, Inc. Figure 10.10-3 Possibility 2 Possibility 1 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2 © 2014 Pearson Education, Inc. Combination 3 Combination 4 1 2 3 combinations possible or Possible Chromosome Combinations or or © 2014 Pearson Education, Inc. Fig. 10-7, p.161 Figure 10.11-1 Prophase I of meiosis Crossing over © 2014 Pearson Education, Inc. Pair of homologs Nonsister chromatids held together during synapsis Figure 10.11-2 Prophase I of meiosis Crossing over Pair of homologs Chiasma Centromere TEM © 2014 Pearson Education, Inc. Nonsister chromatids held together during synapsis Synapsis and crossing over Figure 10.11-3 Prophase I of meiosis Crossing over Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I © 2014 Pearson Education, Inc. Breakdown of proteins holding sister chromatid arms together Figure 10.11-4 Prophase I of meiosis Crossing over Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I Anaphase II © 2014 Pearson Education, Inc. Breakdown of proteins holding sister chromatid arms together Figure 10.11-5 Prophase I of meiosis Crossing over Pair of homologs Chiasma Nonsister chromatids held together during synapsis Synapsis and crossing over Centromere TEM Anaphase I Breakdown of proteins holding sister chromatid arms together Anaphase II Daughter cells Recombinant chromosomes © 2014 Pearson Education, Inc. Random Fertilization Random fertilization adds to genetic variation fusion of 2 gametes (each with 8.4 million possible combinations (from independent assortment)) produces zygote with 70 trillion diploid combinations © 2014 Pearson Education, Inc.