Mitosis and Meiosis

Differences in Human Cell Types Somatic Cells Somatic Cells-“regular” -diploid (46 chromosomes) -Identical DNA throughout body Gamete- Gamete- -sex cells -haploid -sperm and eggs

Mitosis Division of somatic cells Division of somatic cells Necessary for tissue growth or repair Necessary for tissue growth or repair 5 steps 5 steps –DNA must be duplicated –4 step process to divide DNA

Interphase Longest stage of cell’s life cycle Longest stage of cell’s life cycle Part of the cell cycle in which DNA replication occurs Part of the cell cycle in which DNA replication occurs Towards the end, the cell prepares for division Towards the end, the cell prepares for division

Prophase Cell with 2 sets of DNA Cell with 2 sets of DNA Chromatin (loose DNA) condenses into chromosomes Chromatin (loose DNA) condenses into chromosomes First step in which chromosomes are visible. First step in which chromosomes are visible.

Metaphase Chromosomes line up on “equator” of cell Chromosomes line up on “equator” of cell Spindle Fibers attach to centromere (center of chromosome) from centrioles at each pole Spindle Fibers attach to centromere (center of chromosome) from centrioles at each pole

Anaphase Chromosomes are split into two (each still identical) and pulled towards opposite poles. Chromosomes are split into two (each still identical) and pulled towards opposite poles.

Telophase Daughter cells separate by pinching apart Daughter cells separate by pinching apart Nuclear division complete Nuclear division complete Finishes with cytokinesis (division of cytoplasm) Finishes with cytokinesis (division of cytoplasm)

After Mitosis Two identical daughter cells Two identical daughter cells Have identical (diploid) genome Have identical (diploid) genome

Cancer Uncontrolled growth of cells Uncontrolled growth of cells Proteins called oncogens and protooncogens usually control cell cycle Proteins called oncogens and protooncogens usually control cell cycle If they get damaged, cell cycle is uncontrolled If they get damaged, cell cycle is uncontrolled

Meiosis Cell division in gametes Cell division in gametes Same stages as mitosis Same stages as mitosis In meiosis, DNA undergoes another division In meiosis, DNA undergoes another division

Meiosis contd. Leads to 4 haploid daughter cells (23 chromosomes each) Why? Leads to 4 haploid daughter cells (23 chromosomes each) Why? In females, 1 of the daughter cells is retained as ovum In females, 1 of the daughter cells is retained as ovum In males, all 4 become nucleus of sperm In males, all 4 become nucleus of sperm

When Meiosis goes wrong.. Non-disjunction-both chromosomes pulled into one daughter cell, resulting in 47 chromosomes after fertilization Non-disjunction-both chromosomes pulled into one daughter cell, resulting in 47 chromosomes after fertilization

Results Downs syndrome – trisomy 21 Downs syndrome – trisomy 21 Edwards syndrome – trisomy 18 Edwards syndrome – trisomy 18 Patau’s syndrome – trisomy 13 Patau’s syndrome – trisomy 13