Meiosis: Mistakes

1
Meiosis Mistakes Abnormalities

• More variation

2
Common mistakes

• Nondisjunctions altered chromosome
• Deletions, Duplications, Inversions
• Affect parts of a chromosome rather than whole
  thing
• Reciprocal translocations
• Affects two or more chromosomes
• Potentially generates new chromosomes

3
Altered chromosome

• Nondisjunction Members of a chromosome pair fail
  to separate
• In diploids Results in either half OR no normal
  gametes
• Nondisjunction in Meiosis 1

4
Altered chromosome

• Nondisjunction Members of a chromosome pair fail
  to separate
• In diploids Results in either half OR no normal
  gametes
• Nondisjunction in Meiosis II

5
Results in aneuploid zygote

• Normal sperm with n1 egg
• Zygote has trisomy of large chromosome

6
Trisomy 21 Downs

• Three copies of chromosome 21
• Probability of trisomy increases with maternal
  age
• Perhaps due to more time spent in arrested
  development
• Meiosis begins before birth, ends _at_ ovulation

7
Other abnormalities

• Sex chromosome abnormalities are fairly common in
  population, and rarely fatal

8
XXY

• Klinefelter Syndrome
• Underdevelopment of male traits
• Extra X squashes Y influence

9
X0

• Turner Syndrome
• Underdevelopment of female traits
• Need two X chromosomes for normal female
  development

10
Deletions, Duplications, Inversions
11
Reciprocal translocation

• Often results in gene activation at
  inappropriate times.
• May or may not be harmful

12
Leukemia translocation

• This one definitely is harmful
• Causes unchecked cell growth by activating a
  normal growth factor