1. Meiosis and Sexual Reproduction n n 2n Review Question Discussion Question

2. Mitosis Review Single-cell organisms (prokaryotic) carry out Mitosis for asexual reproduction Multi-cell organisms (eukaryotics) carry out Mitosis for growth and repair The phases of mitosis in order are: Prophase, Metaphase, Anaphase, and Telophase Interphase is known as the “resting phase” Cytokinesis occurs at the same time as telophase

3. Through which process do eukaryotic cells reproduce? Requires sex cells from two parents (male and female) Sex cells form as a result of meiosis Offspring are usually not identical Important for the survival of many species ◦ Process results in genetic variation of offspring Sexual Reproduction

4. Define the following terms: Sexual Reproduction Meiosis Gamete Somatic Cells Haploid Textbook pg 46 - 51 Fertilization Zygote Diploid Homologous Pairs

5. New Vocabulary Meiosis: The process that results in the formation of gametes Gametes: Sex cells (egg in females; sperm in males); contains haploid chromosomes Somatic Cells: All body cells except for sex cells; contain Diploid chromosomes Haploid: another term for half; refers to the number of chromosomes; written as n ◦ Chromosomes found singular

6. Fertilization: the union of an egg and a sperm Zygote: Cell that forms as a result of fertilization ◦ Contains Diploid chromosomes (2n) Diploid: Chromosomes found in pairs; written as 2n; Somatic Cells Homologous Chromosomes: Similar chromosomes that are found in pairs; ½ of pair comes from mother, other ½ from father ◦ Human Body somatic cells contain 46 chromosomes, so 23 homologous pairs

7. Meiosis Two division of the nucleus occurs Steps of each division are similar to those of mitosis Meiosis I ◦ Each chromosome is duplicated, similar to mitosis Meiosis II ◦ Two cells that form as a result of Meiosis I divide again ◦ Four daughter cells are produced Video

8. Meiosis Parent cell – chromosome pair Chromosomes copied 1 st division - pairs split 2 nd division – produces 4 gamete cells with ½ the original no. of chromosomes

9. Meiosis I PhaseImageDescription Prophase I - Homologous chromosomes pair together - Crossing over occurs between pairs resulting in genetic variation Metaphase I- Spindle fibers attach to chromosomes and line up in the middle of the cell Anaphase I- Spindle fibers pull the homologous pairs apart - Chromosomes move to opposite sides of the cell Telophase I (& cytokinesis) -Nuclear Membrane forms -Cell splits into two new cells - Cells contain haploid chromosomes (n)

10. Meiosis II PhaseImageDescription Prophase II -new Spindle fibers form and attach to sister chromatids Metaphase II - Spindle fibers attach to sister chromatids and line up in the middle of the cell Anaphase II- Spindle fibers pull the sister chromatids apart - Chromosomes move to opposite sides of the cell Telophase II ( & cytokinesis ) -Nuclear Membrane forms -Each cell splits into two new cells -Forms 4 haploid cells What is the end result of Meiosis?

11. End Results of Meiosis Female Eggs are MUCH larger than male sperm Each haploid cell in males become a gamete ◦ Results in 4 sperm Only 1 of the haploid cells in females become a gamete ◦ Results in 1 egg and 3 polar bodies ◦ Polar bodies are unused and broken down KKKK KKKK Egg Polar Bodies Why does only one gamete form in Females?

12. How do Mitosis and Meiosis differ?

14. The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The first (and distinguishing) division of meiosis

15. Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment. Explain the significant of crossing over. Another Way Meiosis Makes Lots of Different Sex Cells

16. Another Way Meiosis Makes Lots of Different Sex Cells (Gametes) – Independent Assortment Independent assortment produces 2 n distinct gametes, where n = the number of unique chromosomes. That’s a lot of diversity by this mechanism alone. In humans, n = 23 and 2 23 = 6,000,0000.

18. Meiosis – division error Chromosome pair Describe the errors that occur during each division.

19. Meiosis error - fertilization Should the gamete with the chromosome pair be fertilized then the offspring will not be ‘normal’. In humans this often occurs with the 21 st pair – producing a child with Downs Syndrome

20. 21 trisomy – Downs Syndrome Can you see the extra 21 st chromosome?