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Biology LibreTexts

9.S: Changes in Chromosome Number and Structure (Summary)

  • Errors during anaphase in mitosis or meiosis can lead to trisomy and other forms of aneuploidy.
  • Errors during the repair of DNA breaks or during meiotic crossing over can lead to chromosome rearrangements.
  • Five common forms of aneuploidy in humans are 47,sex,+21 (Down syndrome),  47,XYY,  47,XXX,  45,X (Turner syndrome) and  47,XXY (Klinefelter syndrome).
  • Deletion(5) causes a serious condition (cri-du-chat syndrome) because deletions are unbalanced chromosome rearrangements.
  • Inversion(9) causes few health consequences because inversions are balanced chromosome rearrangements.
  • Bright field microscopy can be used to detect chromosome number abnormalities and some chromosome rearrangements.
  • Fluorescence in situ hybridization can be used to detect all types of chromosome abnormalities.
  • PCR and DNA chip based techniques can be used to detect chromosome number abnormalities, deletions, and duplications.

Key Terms:

origin of replication

telomere

centromere

non-disjunction

euploid

aneuploid

balanced

unbalanced

first division nondisjunction

second division nondisjunction

double strand break

nonhomologous end joining

                DNA repair system

chromosome rearrangement

deletion

inversion

paracentric inversion

pericentric inversion

tandem duplication

translocation

reciprocal translocation

Robertsonian translocation

meiotic crossover

deletion loop

karyotype

46,XX

46,XY

47,sex,+21 (Down syndrome)

trisomy

47,XYY

47,XXX

monosomy

45,X (Turner syndrome)

pseudoautosomal region

47,XXY (Klinefelter syndrome)

46,sex,deletion(5)
          (cri-du-chat syndrome)

46,sex,inversion(9)

bright field microscopy

Giemsa stain

fluorescence in situ hybridization

fluorescent probe

DAPI stain

amniocentesis

Contributors