Comparing Plant & Animal Cells Reviewing Mitosis Comparing Plant & Animal Cells

Animal vs. Plant Mitosis Animal Cells Have centrioles! Cytokinesis simple pinching of cell membranes Plant Cells No centrioles Equatorial plate Cytokinesis must form 2 membranes PLUS 2 cell walls

Meiosis Formation of Gametes

Definitions Gamete Sperm Ovum (plural ova) Testes Ovaries Zygote Fertilization Haploid Diploid

Meiosis Two nuclear divisions Creates haploid gametes In animals, sperm and ova In plants, spores Crossing Over occurs 4 daughter cells are created.

Crossing-Over Section 11-4

Meiosis Leads to Genetic Recombination!!!

Meiosis I: Separation of Homologues Prophase I Chromosomes Condense Nuclear Envelope Disappears Spindle Formed (Asters seen here) Homologues Pair Up Crossing-over occurs here!

Figure 11-15 Meiosis Section 11-4 Meiosis I

Metaphase I Homologous chromosomes move to equator

Figure 11-15 Meiosis Section 11-4 Meiosis I

Chromatids do not separate from centromeres! Anaphase I Homologues separate Chromatids do not separate from centromeres!

Figure 11-15 Meiosis Section 11-4 Meiosis I

Telophase I THIS IS REDUCTION DIVISION! Nuclear envelope usually does not reform. Chromosome number in 2 new cells is now half because chromatids did not separate. THIS IS REDUCTION DIVISION! Cytokinesis may or may not occur.

Figure 11-15 Meiosis Section 11-4 Meiosis I

Meiosis II No replication of chromosomes!!!! Proceeds just like mitosis Starts and ends with haploid cells

Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells.

Ovum Formation Meiotic stages are the same One daughter cell keeps ALL of the cytoplasm Other 3 daughter cells only have genetic material – Polar Bodies (Barr Bodies)

Sperm Formation Cytoplasm and Nuclear Material Divides evenly. Flagella are added last to the cells following differentiation Define “differentiation” in your notes here.

Fertilization The haploid sperm and egg fuse to create a diploid zygote.