Lec 6 Outline - 2024 - A01 Biology PDF

HOW IS GENETIC MATERIAL INHERITED? PART 1 Relevant reading: Morris, 4th edition, Chapter 11 & 1  CELL DIVISION The process by which cells make more cells Cell division occurs for: – Growth – Cell replacement – Healing – Reproduction  CELL CYCLE (EUKARYOTES) INTERPHAS...

HOW IS GENETIC MATERIAL INHERITED? PART 1 Relevant reading: Morris, 4th edition, Chapter 11 & 1  CELL DIVISION The process by which cells make more cells Cell division occurs for: – Growth – Cell replacement – Healing – Reproduction  CELL CYCLE (EUKARYOTES) INTERPHASE INTERPHASE 1. G1 phase 2. S phase 3. G2 phase 4. G0 phase  EUKARYOTIC DNA 1 2 3 4 5 ORGANIZATION 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 X CENTROMERES/CHROMATIDS  MITOSIS STAGES: FIG. 11.18 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase + Cytokinesis Chromosomes attach to the mitotic spindle in prometaphase  MITOTIC CELL DIVISION Results in two identical 1. Prophase daughter cells. 2. Prometaphase Each daughter 3. Metaphase cell contains the same number of 4. Anaphase chromosomes as 5. Telophase the parent cell. + Cytokinesis FIG. 11.18 Mitosis.  MEIOTIC CELL DIVISION Results in four daughter cells. Each daughter cell contains half the number of chromosomes as the parent. Each daughter cell is genetically unique. Prophase I (Meiosis I): Steps 1–3 At the start of prophase 1, homologous chromosomes align next to each other, forming the bivalent.  Crossing Over Crossing over during prophase I is a factor in increasing genetic variation because it can result in novel combinations of alleles not seen in the parental chromosomes.  Prophase I (Meiosis I): Steps 4–5 By the end of prophase I, chromosomes are fully condensed, chiasmata are distinct, and the nuclear envelope has broken down.  Prometaphase I and Metaphase I In prometaphase I, the meiotic spindles attach to kinetochores on chromosomes, leading to metaphase I, where bivalents move to the center plane of the nucleus.  Anaphase I and Telophase I At the end of the first meiotic division (anaphase 1 and telophase 1), homologous chromosomes have separated, and the resulting cells are haploid.  Meiosis II No DNA synthesis occurs at the start of meiosis II. During this stage of meiosis, sister chromatids will separate, resulting in gametes. Meiosis II is often called the equational division. MEIOSIS II MEIOSIS II MEIOSIS II COMPARING MITOSIS AND MEIOSIS CYTOPLASMIC DIVISION The Case of the Mysterious Snake Big Surprise http://farm8.staticflickr.com/7042/6871311667_fa56be 2fc2_z.jpg The timber rattlesnake Timber rattlesnake Crotalus horridus Don’t lay eggs Incubate eggs internally so baby snakes are born alive and wriggling Male snakes produce sperm; female snakes produce eggs. http://animals.timduru.org/dirlist/snake/TimberRattlesnak e_01-OnSand.jpg Following mating, the two cells merge inside the female and the fertilized egg develops into a baby snake (with testes or ovaries). http://www.bbc.co.uk/nature/adaptations/Ovoviviparity Professor’s big surprise  One more surprise! It’s a male snake!  MEIOSIS DNA replicates once, but cell divides twice – First meiosis: duplicated, homologous chromosomes pair up at metaphase so each cell gets one set of duplicated chromosomes – Second meiosis: duplicated chromosomes line up independently at metaphase so each cell gets one sister chromatid (i.e. all cells are haploid and have only one copy of each chromosome) Produces gametes with one set of chromosomes – Four gametes (sperm) or one big gamete (egg) & three tiny cells called polar bodies  nucleus nucleus cell nucleus nucleus nucleus nucleus nucleus nucleus nucleus Mitosis Meiosis Cell division Cell division Cell division Cell division Cell division 2X  MEIOSIS: sex chromosomes X Y XY, male X Y X X Y Y X X Y Y  X X Y Y X X Y Y X Y  Genetic Sex Meiosis Determination X X X In Mammals Y Cell division Cell division X X X X X X Y Y Cell division Cell division XY XX X X Y Y X X X X Genetic Sex Meiosis Determination Z Z Z in Birds, Reptiles W Cell division Cell division Z Z Z Z Z Z W W Cell division Cell division ZW ZZ Z Z W W Z Z Z Z  Meiosis Genetic Sex Determination Z Z Z In Birds,Reptiles W Cell division Cell division Z Z Z Z Z Z W W Cell division Cell division ZW ZZ Z Z W W Z Z Z Z CYTOPLASMIC DIVISION