CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 10 Meiosis and Sexual Life Cycles

© 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 ApplicationTechnique Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome 5  m

© 2014 Pearson Education, Inc.  The sex chromosomes are called X and Y  remaining 22 pairs are called autosomes

© 2014 Pearson Education, Inc. Figure 10.4 Key Centromere Pair of homologous chromosomes (one from each set) Sister chromatids of one duplicated chromosome Two nonsister chromatids in a homologous pair 2n  6 Maternal set of chromosomes (n  3) Paternal set of chromosomes (n  3)

© 2014 Pearson Education, Inc. multicelled body meiosis diploid fertilization zygote gametes haploid Fig. 10-8b, p.162 Animal Life Cycle

© 2014 Pearson Education, Inc. Figure 10.6a Key Haploid (n) Diploid (2n) Gametes MEIOSIS FERTILIZATION Zygote n n n 2n2n2n2n Mitosis Diploid multicellular organism (a) Animals

© 2014 Pearson Education, Inc. Figure 10.6b MEIOSIS 2n2n 2n2n FERTILIZATION n n n n n Spores Gametes Mitosis Haploid multi- cellular organism (gametophyte) Zygote Mitosis (b) Plants and some algae Diploid multicellular organism (sporophyte) Key Haploid (n) Diploid (2n)

© 2014 Pearson Education, Inc. Figure 10.6c Key Haploid (n) Diploid (2n) FERTILIZATION n n n n n Mitosis Haploid unicellular or multicellular organism Gametes Zygote 2n2n MEIOSIS (c) Most fungi and some protists

© 2014 Pearson Education, Inc. 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 Duplicated pair of homologous chromosomes Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Diploid cell with duplicated chromosomes Sister chromatids Homologous chromosomes separate Sister chromatids separate Haploid cells with duplicated chromosomes Meiosis I Meiosis II Haploid cells with unduplicated chromosomes 1 2

© 2014 Pearson Education, Inc. Figure 10.7a Interphase Duplicated pair of homologous chromosomes Pair of homologous chromosomes in diploid parent cell Chromosomes duplicate Diploid cell with duplicated chromosomes Sister chromatids

© 2014 Pearson Education, Inc. Figure 10.7b Homologous chromosomes separate Sister chromatids separate Haploid cells with duplicated chromosomes Meiosis I Meiosis II Haploid cells with unduplicated chromosomes 1 2

© 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 IMetaphase IAnaphase I Telophase I and Cytokinesis Sister chromatids Centromere (with kinetochore) Sister chromatids remain attached Centrosome (with centriole pair) Metaphase plate Chiasmata Spindle Cleavage furrow Homologous chromosomes separate Microtubule attached to kinetochore Fragments of nuclear envelope Homologous chromosomes

© 2014 Pearson Education, Inc. Figure 10.8b MEIOSIS II: Separates sister chromatids Prophase IIMetaphase IIAnaphase 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 MITOSISMEIOSIS Prophase Duplicated chromosome Metaphase Anaphase Telophase 2n2n2n2n Daughter cells of mitosis Sister chromatids separate. Individual chromosomes line up. Chromosome duplication Parent cell 2n = 6 Chromosome duplication Pairs of chromosomes line up. Chiasma MEIOSIS I Prophase I Metaphase I Homologous chromosome pair Anaphase I Telophase I MEIOSIS II Homologs separate. Sister chromatids separate. Daughter cells of meiosis II nn nn Daughter cells of meiosis I

© 2014 Pearson Education, Inc. Figure 10.9aa MITOSISMEIOSIS Prophase Duplicated chromosome Metaphase Individual chromosomes line up. Chromosome duplication Parent cell 2n = 6 Chromosome duplication Pairs of chromosomes line up. Chiasma MEIOSIS I Prophase I Metaphase I Homologous chromosome pair

© 2014 Pearson Education, Inc. Figure 10.9ab MITOSIS MEIOSIS Anaphase Telophase 2n2n2n2n Daughter cells of mitosis Sister chromatids separate. Anaphase I Telophase I MEIOSIS II Homologs separate. Sister chromatids separate. Daughter cells of meiosis II nn nn Daughter cells of meiosis I

© 2014 Pearson Education, Inc. Figure 10.9b DNA replication Number of divisions Synapsis of homologous chromosomes Number of daughter cells and genetic composition Role in the animal body Occurs during interphase before mitosis begins One, including prophase, prometaphase, metaphase, anaphase, and telophase Does not occur Two, each diploid (2n) and genetically identical to the parent cell Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Occurs during interphase before meiosis I begins Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Produces gametes; reduces number of chromosome sets by half and introduces genetic variability among the gametes SUMMARY MeiosisMitosisProperty

© 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: 2 n (and this is without crossing over)

© 2014 Pearson Education, Inc. Possible Chromosome Combinations 2 n for humans would be … 2 23 or… 8,388,608

© 2014 Pearson Education, Inc. Figure Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I

© 2014 Pearson Education, Inc. Figure Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II

© 2014 Pearson Education, Inc. Figure Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1Combination 2Combination 3Combination 4

© 2014 Pearson Education, Inc. or 123 combinations possible Fig. 10-7, p.161 Possible Chromosome Combinations

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Nonsister chromatids held together during synapsis Crossing over

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Synapsis and crossing over Nonsister chromatids held together during synapsis Crossing over

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Nonsister chromatids held together during synapsis Crossing over

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Anaphase II Nonsister chromatids held together during synapsis Crossing over

© 2014 Pearson Education, Inc. Figure Prophase I of meiosis Pair of homologs Chiasma Centromere TEM Anaphase I Synapsis and crossing over Breakdown of proteins holding sister chromatid arms together Anaphase II Daughter cells Recombinant chromosomes Nonsister chromatids held together during synapsis Crossing over

© 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