When Meiosis goes wrong…

1. When Meiosis goes wrong… 1.10.12

2. What can go wrong during meiosis?

3. What can go wrong during meiosis? • Nondisjunction – The failure of homologous chromosomes or non-sister chromatids to separate during anaphase I or anaphase II

4. What can go wrong during meiosis? • Nondisjunction – The failure of homologous chromosomes or non-sister chromatids to separate during anaphase I or anaphase II • One gamete ends up with two copies of a chromosome, the other with zero • Mitosis then spreads this chromosomal error throughout the organism

5. Alteration of Chromosome # • Trisomy = 3 copies of a particular chromosome • Monosomy = 1 copy

6. Alteration of Chromosome # • Trisomy = 3 copies of a particular chromosome • Monosomy = 1 copy • Polyploidy = double/triple/etc. of entire genome (whole set of chromosomes) • Kills animals (prevents development), but makes plants bigger and stronger • Can occur from 2 sperm fertilizing 1 egg or by a diploid gamete

7. Alteration of Chromosome # • It is common for humans to have an irregular # of chromosomes, but usually disastrous • 1/3 of all pregnancies end in spontaneous abortions (natural miscarriage), and ½ of these are due to nondisjunction

8. Down’s Syndrome (Trisomy 21)

9. Down’s Syndrome (Trisomy 21) • 3 copies of chromosome #21 • 1 in 500 children in U.S. • Flattened face, short stature, mental retardation, shortened lifespan, heart defects, sterile

10. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30

11. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952

12. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35

13. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378

14. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40

15. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106

16. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106 • Under 45

17. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106 • Under 45 1 in 30

18. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106 • Under 45 1 in 30 • Under 50

19. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106 • Under 45 1 in 30 • Under 50 1 in 11

20. Down’s Syndrome (Trisomy 21) • Occurrence directly related to maternal age • Under 30 1 in 952 • Under 35 1 in 378 • Under 40 1 in 106 • Under 45 1 in 30 • Under 50 1 in 11 • Trisomy 13, 15, and 18 also occur, but die shortly after birth. All other human trisomies fail to develop

21. Nondisjunction of Sex Chromosomes • Far less serious • Why? • Y chromosome carries very few genes • X chromosome will mostly shrivel up into an inactive state if an extra is present (Barr body)

22. Klinefelter’s Syndrome (XXY) • 1 in 2,000 births • Underdeveloped male sex organs • Feminine secondary characteristics • Sterile

23. XYY • 1 in 1,000 • Normal looking male • Tall with relatively severe acne

24. XXX • 1 in 1,000 • Tall female with irregular menstrual cycle • Otherwise normal, needs karyotype(picture of chromosomes) for diagnosis

25. Turner’s Syndrome (XO)

26. Turner’s Syndrome (XO) • 1 in 2,000 female births • Only viable monosomy(the only chromosome that humans can survive with only one copy of)

27. Turner’s Syndrome (XO) • 1 in 2,000 female births • Only viable monosomy(the only chromosome that humans can survive with only one copy of) • Normal until puberty • Short, sterile, no secondary sex characteristics, normal intellect, treatable with hormone therapy