Meiosis: Special Nuclear Division (PDF)

## Meiosis **Special Nuclear Division** * **Sexual Reproduction** * Makes a more genetically diverse population. * Asexual reproduction (like in bacteria) is great in a stable environment. * But sexual reproduction and its genetic diversity are key to survival in a changing env...

## Meiosis **Special Nuclear Division** * **Sexual Reproduction** * Makes a more genetically diverse population. * Asexual reproduction (like in bacteria) is great in a stable environment. * But sexual reproduction and its genetic diversity are key to survival in a changing environment. * **GAMETES** are required for sexual reproduction. * GAMETES = eggs and sperm. * Meiosis helps make gametes. * So meiosis makes sexual reproduction possible. * **Meiosis: The process helps produce GAMETES** * **Males** produce gametes called **SPERM**. * **Females** produce gametes called **EGGS**. * **A few facts about the human Gametes?** * **For males,** * Sperm are made fresh daily. * **For females,** * All the eggs a woman will have are made **BEFORE** she is born. * Females release one egg every month once they hit puberty. * Sometimes they release two or three. This is when Fraternal twins and Fraternal triplets can be conceived. * **Why Meiosis?** * Humans have 46 chromosomes in each cell. * A full set (46) is called **diploid**. * A baby needs a total of 46 chromosomes in the first cell. * 23 from Mom and 23 from Dad, 23 + 23 = 46. * A half set (23) is called **haploid**. * Therefore, we need to take a **DIPLOID** cell with 46 chromosomes and make **HAPLOID** cells with 23 chromosomes. * This is called **Meiosis**. * There are 8 phases in **MEIOSIS**. * **The 46 Chromosomes** * There are 23 pairs of chromosomes. * The 23rd pair of chromosomes determines the sex. * XX = Female * XY = Male * **Stages of Meiosis** * Prophase 1 * Metaphase 1 * Anaphase 1 * Telephase 1 * Prophase 2 * Metaphase 2 * Anaphase 2 * Telephase 2 * **Meiosis Produces Sperm in Males** * **Diploid** cell (with 46 chromosomes). * After Meiosis 1, 2 **haploid** cells are produced (23 chromosomes each). * After Meiosis II, 4 **haploid** cells are produced (23 chromosomes each). * Tails grow later. * **Meiosis Produces Egg in Females** * **Diploid** cell (with 46 chromosomes). * After Meiosis 1, 1 large **haploid** cell and 1 **polar body** are produced (both with 23 chromosomes). * After Meiosis II, 1 large **haploid** cell and 3 **polar bodies** are produced (all with 23 chromosomes). * Polar bodies are reabsorbed. * **Compare** | | **Mitosis** | **Meiosis** | |------------------------------------|:--------------------------------------------|:----------------------------------------------| | **This is used for what?** | To grow and replace damaged body cells | To make gametes for sexual reproduction | | **From one cell, produces...** | 2 cells | 4 cells | | **Compared to parent cell, each daughter cell is...** | genetically identical | genetically different | | **Kind of cell (how much of the original DNA?)** | **Diploid** (full set of DNA: 46 chromosomes) | **Haploid** (half set of DNA: 23 chromosomes) |