ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE

1
ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE

• A karyotype is a photographic inventory of an
  individuals chromosomes
• Human female karyotype

2
An extra copy of chromosome 21 causes Down
syndrome

• This karyotype shows three number 21 chromosomes
  trisomy 21
• An extra copy of chromosome 21 causes Down
  syndrome
• The chance of having a Down syndrome child goes
  up with maternal age

3
Accidents during meiosis can alter chromosome
number

• Abnormal chromosome count is a result of
  nondisjunction

4
Abnormal numbers of sex chromosomes do not
usually affect survival

• Nondisjunction can also produce gametes with
  extra or missing sex chromosomes
• A man with Klinefelter syndrome has an extra X
  chromosome
• A woman with Turner syndrome lacks an X
  chromosome

5
Alterations of chromosome structure can cause
birth defects and cancer
Deletion

• Chromosome breakage can lead to rearrangements
  that can produce genetic disorders or cancer
• Four types of rearrangement are deletion,
  duplication, inversion, and translocation

Duplication
Inversion
Reciprocaltranslocation
Nonhomologouschromosomes
6
Chromosomal changes in a somatic cell can cause
cancer

• A chromosomal translocation in the bone marrow is
  associated with chronic myelogenous leukemia

Chromosome 9
Reciprocaltranslocation
Chromosome 22
Philadelphia chromosome
Activated cancer-causing gene