Honors Biology class PPt on the process of meiosis; used following Mitosis

1. Meiosis

2. What is it? Mitosis occurs, producing two identical daughter cells Only eukaryotic cells In humans, all cells but one type Involve diploid cells (2n) Humans reproduce sexually Sex cells = gametes = sperm & egg Meiosis is the making of gametes

3. Where does it happen? Made in reproductive organs Males: testes  sperm Females: ovaries  ova (eggs) Gametes contain 23 chromosomes Haploid cells (n) Mitosis involves the halving of the normal chromosome number

4. Creation of offspring Fertilization 23 + 23 = 46 n + n = 2n

5. Chromosomes Humans contain 23 pairs of chromosomes (46 total) Half from each parent Pairs 1 through 22 are homologous pairs Same size Carry genes for same traits Not identical

7. Abnormalities Nondisjunction- “failure to separate” Trisomy: three of one type of chromosome Trisomy 21: Down Syndrome Monosomy: one of one type of chromosome Klinefelter’s XXY (23rd pair) Turner’s Syndrome XO (23rd pair)

8. Meiosis Serves to halve the number of chromosomes, creating gametes In humans: Male gametes – 4 haploid sperm Female gametes – 1 haploid egg, 3 polar bodies Meiosis I & Meiosis II

9. Meiosis I Separates homologous pairs

10. Crossing OverIncreases Genetic Variability

14. Meiosis II No duplication of chromosomes between Meiosis I & II Meiosis II separates sister chromatids

16. Meiosis II Results Four daughter cells Contain half as many (n) chromosomes as parent (2n) Each cell is genetically different Fertilization restores chromosome number to 2n

17. Meiosis in Humans Formation of gametes Males: Spermatogeneis

18. Meiosis in Humans Formation of gametes Females: Oogeneis Meiosis I 1 diploid cell 1 polar body Meiosis II 1 haploid gamete 3 haploid polar bodies Result 1 egg

19. Genetic Variations Crossing over Shuffle genes on chromosomes Independent assortment of homologous pairs Arrange randomly on metaphase plate 223 (or 8 million) possibilities Random fertilization 8 million egg x 8 million sperm = 64 trillion zygote