Meiosis
Vocabulary 1. Parent cell: original cell before division 2. Daughter cell: cells after division 3. Gamete/sex cell: eggs and sperm 4. Somatic cell: all other body cells besides eggs and sperm 5. Haploid (n): one set of unique chromosomes 6. Diploid (2n): two sets of unique
Vocabulary 7. Alleles: different forms of a gene. For example, there are at least two different alleles for eye color. Different combinations of alleles give organisms different variations of the same trait, such as brown eyes or blue eyes. 8. Homologous chromosomes: chromosomes that are similar, but not identical. For example, the larger chromosomes to the left are homologous to each other, and the smaller chromosomes are homologous to each other. They may not have the exact same alleles, but they have the same genes in the same places (and the same chromosome number). 9. Non-homologous chromosomes: chromosomes that are not similar at all. In the picture on the left, the large and small chromosomes are non-homologous because they carry different genes.
Vocabulary 10. Sister chromatids: identical halves of a chromosome that has replicated 11. Tetrad: a complex of 4 homologous chromatids
Vocabulary 12. Chromosome: a molecule of DNA 13. Fertilization: when an egg cell and a sperm cell join to form a zygote 14. Zygote: a fertilized egg that has not yet started to divide 15. Mitosis: the process of cell division that results in two identical daughter cells (2n 2n) 16. Meiosis: the process of cell division that results in four haploid sex cells (2n n)
Vocabulary 17. Karyotype: the number and visual appearance of the chromosomes in the cell nuclei of an organism or species. (This is a picture of a normal karyotype. Is this individual male or female?)
Key Point #1: Mitosis and Meiosis are two different types of cell division Mitosis vs. -Mitosis creates two identical daughter cells from one parent cell -ALL of your somatic cells do mitosis -after mitosis, the daughter cells have the same number of chromosomes as the parent cell (2n 2n) Meiosis -Meiosis creates four unique daughter cells from one parent cell -Meiosis is ONLY used to make sex cells -each daughter cell has HALF the number of chromosomes as the parent cell (2nn)
Key Point #2: Mitosis is cell division that results in two diploid cells identical to the original cell The diploid (2n) parent cell replicates its DNA to go from I-shaped to X-shaped double chromosomes The parent cell divides (splitting the X shaped double chromosomes into I-shaped single chromosomes) to create two identical cells that are both 2n. Do you want all of your skin cells to be different, or the same?
Check for Understanding If a skin cell with 46 chromosomes undergoes mitosis, how many chromosomes will each daughter cell have? If two daughter cells in a cabbage leaf have 18 chromosomes each, how many chromosomes did the parent cell have?
Key Point #3: Meiosis is two cell divisions that results in four haploid, non- in non- identical daughter cells Step 1: The parent cell duplicates (copies) its DNA. The chromosomes have gone from I shaped to X shaped. This cell is still considered diploid (Why?). Step 2: The parent cell divides to make two haploid daughter cells (the X shaped chromosomes split up) Step 3: Each daughter cell divides. The X shaped chromosomes split into I shaped chromosomes to make a total of 4 haploid daughter cells
Key Point #4: Meiosis only happens in reproductive organs to create sex cells In females, meiosis happens in the ovaries to create egg cells. In males, meiosis happens in the testes to make sperm cells. Egg and sperm cells are called gametes.
Meiosis Diagram -The parent cell is diploid (2n) and has 2 of each chromosome. -After the DNA duplicates and the chromosomes are X shaped, the cell is still considered diploid. -The parent cell divides and one chromosome from each pair goes to each cell. The daughter cells are now haploid, but the chromosomes are still in duplicate form, so they are still X-shaped. -Each haploid (n) cell divides into 2 daughter cells that are also haploid (the duplicated X shaped chromosomes separate into I shaped chromosomes)
Filling in the Diagram (write this in your notes) In humans, this is the number of chromosomes in each cell during meiosis. So what about frogs? Frogs are diploid and have 26 chromosomes in their somatic cells. Copy this meiosis diagram for Sparky.
Check for Understanding Copy this meiosis diagram for coyotes. Coyotes are diploid and have 76 chromosomes in their somatic cells.
Check for Understanding If a human somatic cell has 46 chromosomes, how many chromosomes would there be in a human cell after meiosis? If a goat gamete produced during meiosis has 30 chromosomes, how many chromosomes would a goat skin cell have? Assume goats are diploid.