CH. 13 – CHROMOSOMES, ETC.
I. SEX CHROMOSOMES & SEX DETERMINATION
A. CHROMOSOMES 46 (23 pairs)
1. KARYOTYPE - Shows chromosomes in cell (p. 191)
2. Autosomes - 44 (22 pairs)
3. Sex chromosomes - 2: X & Y (p. 241)
a. XX = female
b. XY = male SRY gene (p. 242)
TDF-testis determining factor, 6-7 weeks
B. PRIMARY SEX RATIO 1:1 at fertilization
1. Determined by male
2. Punnet square:
3. 1/2 chance of male; 1/2 chance of female; “Pascal’s triangle”
II. SEX-LINKED (X-LINKED) RECESSIVE INHERITANCE
A. PATTERNS Females Males
XX - normal XY - normal
XcX - normal, but carrier XcY - affected
XcXc - affected
B. DISEASES - males always more affected
1. Color blindness - red/green; 5-9% caucasian males
2. Hemophilia - bleeder's disease (p. 242)
C. Y-LINKED TRAITS
1. maleness determined
2. "hairy ears" syndrome
3. smaller chromosome; fewer traits
III. MISTAKES IN MEIOSIS
A. ABNORMALITIES IN CHROMOSOME NUMBER
1. Monosomy - Missing 1 or more chromosomes è 45 or less
2. Trisomy - Extra copy of a chromosome è 47 or more
3. WHY? - NONDISJUNCTION = Failure of chromatids to separate
during anaphase II of meiosis.
4. Down's syndrome (3 of chromosome #21) in offspring (p. 250)
increases for women over 35 and men over 55 - WHY? (p. 249)
5. SEX CHROMOSOMES (p. 251)
B. ABNORMALITIES IN CHROMOSOME STRUCTURE (see p. 301)
1. Deletion - part missing, most serious
a. Prader-Willi syndrome – missing part of chrom #15 (read p. 251)
2. Duplication - ABCD è ABBCCD
3. Inversion - ABCD è ACBD
4. Translocation - part broken off one and added to another
a. Robertsonian = just like Downs syndrome
C. GENETIC TESTING
1. Genetic counseling & pedigree analysis
2. AMNIOCENTESIS (p. 252)
3. Chorionic villi sampling (p. 253)