1. AP Biology AP Question of the Day Which is true about a testcross? A. It is a mating between 2 hybrid individuals B. It is a mating between a hybrid and homozygous recessive individual C. It is a mating between an individual with an unknown genotype and a homozygous recessive individual D. It is a mating to determine which individual is homozygous recessive

2. AP Biology Today…  Human chromosomal disorders  Case Study

3. AP Biology 2006-2007 Human Genetics and Disorders

4. AP Biology Chromosomal Abnormalities  Nondisjunction  chromosomes don’t separate properly during meiosis  Chromosomal Mutations  deletion  duplication  inversion  translocation

5. 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

6. AP Biology Autosomal Disorders  Dominant  Acondroplasia  Dwarfism  Lethal in homozygous cond.  Acromegaly  Gigantism  Overactive pituitary  Huntington’s  Degeneration of nervous system  Manifests around 40 years of age  Recessive  Albinism  Melanin pathway mutated  photosensitivity  Phenylketoneuria  Cannot break down phenylalanine  Lead to mental retardation  Cystic fibrosis  Cl - channel problem  Mucus buildup  Death around 40

7. 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 - aneuploidy 2n n n n-1 n+1

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

9. AP Biology trisomy 2n+1 Nondisjunction  Cause of aneuploidy (wrong chromosome #)  trisomy  cells have 3 copies of a chromosome  monosomy  cells have only 1 copy of a chromosome n+1 n monosomy 2n-1 n-1 n

10. 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

11. 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

12. AP Biology Sex Chromosomes Abnormalities  Human development more tolerant of wrong numbers in sex chromosome  Cause is nondisjunction  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

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

14. AP Biology Case Study  Put your genetics knowledge into practice!  Work with a partner on the case study.  Due next time.