Meiosis

Fig. 13-3b TECHNIQUE Pair of homologous replicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 µm

Fig Key Haploid (n) Diploid (2n) n n Gametes n n n Mitosis MEIOSIS FERTILIZATION MEIOSIS 2n2n 2n2n Zygote 2n2n Mitosis Diploid multicellular organism (a) Animals Spores Diploid multicellular organism (sporophyte) (b) Plants and some algae 2n2n Mitosis Gametes Mitosis n n n Zygote FERTILIZATION n n n Mitosis Zygote (c) Most fungi and some protists MEIOSIS FERTILIZATION 2n2n Gametes n n Mitosis Haploid multi- cellular organism (gametophyte) Haploid unicellular or multicellular organism

Key Haploid (n) Diploid (2n) n n n n n 2n2n 2n2n Mitosis Zygote Spores Gametes MEIOSISFERTILIZATION Diploid multicellular organism (sporophyte) Haploid multi- cellular organism (gametophyte) (b) Plants and some algae

Terms to know... o Somatic vs germ line cells o Chromosomes (13.6) o Chromatids o Homologous o Autosomes vs sex chromosomes o Locus

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

Key Haploid (n) Diploid (2n) Haploid gametes (n = 23) Egg (n) Sperm (n) MEIOSISFERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

 Different Chromosome Numbers Are Found in One Organism  Gametes contain half as many chromosomes as somatic cells  Zygotes are produced by fusion of gametes  Fusion of gametes is called fertilization or syngamy  Meiosis serves to stabilize the chromosomes number  Is a reduction division process  Gametes are haploid and possess a single set of genetic material  An individual inherits genes from its father and its mother

I.Sexual Reproduction Varies by Kingdom A. Unicellular organisms 1. Individual cells function directly as gametes 2. Zygote may divide mitotically or meiotically B. Plants 1. Haploid cells are produced through meiosis 2. Cells divide mitotically to form multicellular haploid phase 3. Special haploid cells differentiate into eggs or sperm C. Animals 1. Gamete-producing cells differentiate from somatic cells early 2. Referred to as germ line cells 3. Somatic cells are diploid and reproduce by mitosis 4. Diploid gamete-producing cells, produce haploid gametes by meiosis

 If you think you can you can.  If you think you can’t you're right.

Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Prophase II Metaphase IIAnaphase II Telophase II and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow Sister chromatids separate Haploid daughter cells forming

Meiosis I o Interphase: replication o Each chromosome = 2 sister chromatids o Prophase I: o Condensation of chromatin o Synapsis o Tetrads form o Crossing chiasmata o Centrosomes separate, spindles form, bind to kinetochores

Meiosis I o Metaphase I: o Tetrads line up on metaphase plate o Anaphase I: o Chromosomes (each = 2 sister chromatids) move to poles o Pulled along fibers by kinetochore o Centromeres don’t separate o Telophase/cytokinesis o Cleavage furrow o N set of each pole o DAUGHTER CELLS ARE HAPLOID

Fig. 13-8b Prophase IMetaphase I Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Centromere (with kinetochore) Metaphase plate Homologous chromosomes Fragments of nuclear envelope Microtubule attached to kinetochore

Fig. 13-UN4

Fig. 13-8c Anaphase I Telophase I and Cytokinesis Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow

Fig. 13-8d Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming

Meiosis II(NO INTERPHASE) o Prophase II o New spindle fibers form o Chromosomes move to middle o Metaphase II: o Chromosomes on metaphase plate o Anaphase II: o Centromeres/sister chromatids separate o Each chromosome now = 1 chromatid o Telophase II/cytokinesis o Nuclear membrane forms

Fig. 13-8e Prophase IIMetaphase II

Fig. 13-8f Anaphase II Telephase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming

Fig Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Prophase II Metaphase IIAnaphase II Telophase II and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Sister chromatids remain attached Homologous chromosomes separate Cleavage furrow Sister chromatids separate Haploid daughter cells forming

Fig. 13-UN1 Prophase I: Each homologous pair undergoes synapsis and crossing over between nonsister chromatids. Metaphase I: Chromosomes line up as homolo- gous pairs on the metaphase plate. Anaphase I: Homologs separate from each other; sister chromatids remain joined at the centromere.

Fig SUMMARY Meiosis Mitosis Property DNA replication Number of divisions Occurs during interphase before mitosis begins One, including prophase, metaphase, anaphase, and telophase Synapsis of homologous chromosomes Does not occur Number of daughter cells and genetic composition Two, each diploid (2n) and genetically identical to the parent cell Role in the animal body 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 chromosomes by half and introduces genetic variability among the gametes

OOGENESIS/SPERMATOGENESIS

Genetic Variation o Independent assortment of maternal/paternal chromosomes (13.9) o How many pairs in a human?!?!? o Crossing over o Exchange b/w homologous chromosmes o Recombinant: genetic info from 2 sources o Sister chromatids  identical o Random fertilization