2. AP Biology 2006-2007 Errors of Meiosis Chromosomal Abnormalities

3. AP Biology Chromosomal abnormalities  Incorrect number of chromosomes  nondisjunction  chromosomes don’t separate properly during meiosis  breakage of chromosomes  deletion  duplication  inversion  translocation

4. AP Biology Nondisjunction  Problems with meiotic spindle cause errors in daughter cells  homologous chromosomes do not separate properly during Meiosis 1  sister chromatids fail to separate during Meiosis 2  too many or too few chromosomes 2n n n n-1 n+1

5. AP Biology Alteration of chromosome number all with incorrect number1/2 with incorrect number error in Meiosis 1 error in Meiosis 2

6. AP Biology trisomy 2n+1 Nondisjunction  Baby has wrong chromosome number  trisomy  cells have 3 copies of a chromosome  monosomy  cells have only 1 copy of a chromosome n+1n monosomy 2n-1 n-1n

7. AP Biology Human chromosome disorders  High frequency in humans  most embryos are spontaneously aborted  alterations are too disastrous  developmental problems result from biochemical imbalance  imbalance in regulatory molecules?  hormones?  transcription factors?  Certain conditions are tolerated  upset the balance less = survivable  but characteristic set of symptoms = syndrome

8. AP Biology Down syndrome  Trisomy 21  3 copies of chromosome 21  1 in 700 children born in U.S.  Chromosome 21 is the smallest human chromosome  but still severe effects  Frequency of Down syndrome correlates with the age of the mother

9. AP Biology Down syndrome & age of mother Mother’s age Incidence of Down Syndrome Under 30<1 in 1000 301 in 900 351 in 400 361 in 300 371 in 230 381 in 180 391 in 135 401 in 105 421 in 60 441 in 35 461 in 20 481 in 16 491 in 12 Rate of miscarriage due to amniocentesis:  1970s data 0.5%, or 1 in 200 pregnancies  2006 data <0.1%, or 1 in 1600 pregnancies

10. AP Biology Genetic testing  Amniocentesis in 2nd trimester  sample of embryo cells  stain & photograph chromosomes  Analysis of karyotype

11. AP Biology Sex chromosomes abnormalities  Human development more tolerant of wrong numbers in sex chromosome  But produces a variety of distinct syndromes in humans  XXY = Klinefelter’s syndrome male  XXX = Trisomy X female  XYY = Jacob’s syndrome male  XO = Turner syndrome female

12. AP Biology  XXY male  one in every 2000 live births  have male sex organs, but are sterile  feminine characteristics  some breast development  lack of facial hair  tall  normal intelligence Klinefelter’s syndrome

13. AP Biology Klinefelter’s syndrome

14. AP Biology Jacob’s syndrome male  XYY Males  1 in 1000 live male births  extra Y chromosome  slightly taller than average  more active  normal intelligence, slight learning disabilities  delayed emotional maturity  normal sexual development

15. AP Biology Trisomy X  XXX  1 in every 2000 live births  produces healthy females  Why?  Barr bodies  all but one X chromosome is inactivated

16. AP Biology Turner syndrome  Monosomy X or X0  1 in every 5000 births  varied degree of effects  webbed neck  short stature  sterile

17. AP Biology Changes in chromosome structure  deletion  loss of a chromosomal segment  duplication  repeat a segment  inversion  reverses a segment  translocation  move segment from one chromosome to another error of replication error of crossing over

18. AP Biology Some Different Chromosomal Systems of Sex determination  XO system – Grasshoppers, Cockroaches, and some other insects there is only one type of sex chromosome – X  Females are XX and males are X (XO)

19. AP Biology The Z-W system – In birds, some fishes, and some insects, the sex chromosomes present in the egg determine the sex of the offspring. Females are ZW and males are ZZ

20. AP Biology The haplo-diploid system  There are no sex chromosomes in most species of bees and ants. Females develop from fertilized eggs and are diploid and males develop from unfertilized eggs are are haploid – They have no fathers.

21. AP Biology X-Inactivation in Female Mammals  Barr Body- inactivated X chromosome that lies along the inside of the nuclear envelope.  Involves the methylation of DNA (attachment of a -CH 3 to one of the nitrogenous bases)  Tortoise Shell Cat – Coat color in cats is on the X chromosome so females can have orange and black hair, but not males.

22. AP Biology Here Kitty, Kitty, Kitty!

23. AP Biology Genomic Imprinting  Genomic Imprinting -a process whereby only one gene copy is expressed, either the maternal or paternal allele  May lead to disease.  Diseases: Prader Willi - Paternal  Angelman Syndrome- Maternal  Certain Cancers (Wilm’s tumor) Same gene

24. AP Biology Prader-Willi Syndrome

25. AP Biology Prader-Willi Syndrome

26. AP Biology Angelman’s Syndrome

27. AP Biology Wilm’s Tumor

28. AP Biology 2006-2007 Don’t hide… Ask Questions!!