Sex Determination & Nondisjunction Disorders

1. Sex Determination& Nondisjunction Disorders

2. Karyotype Human Karyotype: • 46 chromosomes organized in 23 pairs in order of decreasing size • Pairs # 1-22: • autosomes • somatic (body) chromosomes • all 22 pairs are homologous • Pair # 23: • sex chromosomes • contain genes that code for sexual characteristics

3. Female Karyotype • XX • homologous pair • 2 sets of genes for every trait

4. Sex Chromosomes • XY • not homologous (no pair) • each one contains different genes • males only have 1 copy of genes on X & Y chromosome

5. Sex Determination XY Who determines the gender of offspring in humans? • all eggs carry one X chromosome • ½ of sperm carry one X chromosomes • ½ of sperm carry one Y chromosomes • Therefore: male determines the gender XX meiosis X Y X X eggs sperm X Y X X

6. Nondisjunction Disorders anaphase I

7. Nondisjunction: one pair of homologous chromosome doesn’t separate during anaphase I Result: ½ gametes have one chromosome too few other ½ gametes have one chromosome too many in females, nondisjunction occurs more often if >35 years old Nondisjunction Disorders missing one chromosome one extra chromosome

8. amniocentesis: recommended for all women over 35 years old fetal cells removed with a needle from amniotic fluid karyotype of fetal cells examined for nondisjunction disorders Nondisjunction Disorders http://pregnancy.healthguru.com/content/video/watch/100062/Understanding_Amniocentesis?HG_Google_Video_Sitemap=

9. Chromosomal Abnormalities occur when a normal gamete (n = ___)joins with a gamete that has: n + 1: individual will have ______________________ n - 1: individual will have ______________________ in either case the resulting individual will suffer from some disabilities depending on which chromosomes are involved Chromosomal Abnormalities 23 (24) 47 (1 chromosome too many) (22) 45 (1 chromosome less)

10. Nondisjunction Disorders Common Examples: Down Syndrome trisomy 21 Klinefelter’s syndrome XXY Turner’s syndrome X0 monosomy Trisomic female (super female) XXX Jacob’s syndrome (super male) XYY (47) male (47) female (45) (47) (47)

11. Chromosomal Abnormalities • Down Syndrome • trisomy 21

12. Chromosomal Abnormalities • Down Syndrome • developmental delays • physical abnormalities • short • folds around eyes • stubby fingers & toes • large protruding tongue • weak muscles • heart defects

13. Chromosomal Abnormalities • Klinefelter’s syndrome • XXY • male

14. Chromosomal Abnormalities • Klinefelter’s syndrome • tall • small testicles • after puberty develop some feminine traits (ex. breasts) • sterile

15. Chromosomal Abnormalities • Trisomic Female • XXX • super female • have very few problems • most are fertile

16. Chromosomal Abnormalities • Turner’s syndrome • XO • female

17. Chromosomal Abnormalities • Turner’s syndrome • short • thick neck • never goes through puberty • sterile 15 year old

18. Chromosomal Abnormalities • Jacob’s syndrome • XYY • super male • very tall • low mental ability • often aggressive

19. FUN QUIZ • Fill out the Atypical Meiosis Sheet • 7 min • Switch with the person behind you • 1 mark for every fill in the blank correct • Total in top right hand corner • Hand in to me!

20. Homework • Karyotype Assignment