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.

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 –Crossing-over occurs here!

Metaphase I Homologous chromosomes move to equator

Anaphase I Homologues separate Chromatids do not separate from centromeres!

Telophase I 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.

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

Draw a sperm and egg uniting to form a zygote. Be sure to include the number of chromosomes for each.

Using 2 different colored pencils, draw two homologous chromosomes before and after they cross over.