3.1 - Chromosomal Changes Flashcards
3 Types of Chromosomal Changes
1) Changes in parts
2) Aneuploidy
3) Polyploidy
Aneuploidy
- Abnormal number of chromosomes in cell
- monosomics & trisomics
ex: 45 or 47 instead of usual 46
Polyploidy
- More than 2 chromosome sets
ex: 3n (triploid), 4n (tetraploid), 5n (pentaploid), 6n (hexaploid), etc.
Deletions
- Chromosomal Changes: Parts
- Part of a chromosome or a sequence of DNA is lost during DNA replication.
Cytological detection of deletions
1) smaller
2) missing bands
3) centromere location appears to change (acrocentric to metacentric)
Duplications
- Chromosomal Changes: Parts
- Part of a chromosome or a sequence of DNA is duplicated during DNA replication
Cytological detection of duplications
1) larger
2) duplicated bands
3) Centromere location appears to change
Inversions
- Chromosomal Changes: Parts
- Part of a chromosome or a sequence of DNA inverses during DNA replication
Cytological detection of inversions
1) no size change
2) inverted banding pattern
3) centromere location (depends)
Paracentric inversion
A B C D E
A D C B E
- inversion is “outside” the centromere, does not include it
- dicentric bridge breaks randomly
Pericentric inversion
A B C D E
A D C B E
-inversion surrounds the centromere
Pericentric/Paracentric inversions result in…
- 2 unbalanced gametes (inviable)
- 1 normal gamete (no inversion)
- 1 inversion gamete (still viable)
Translocations
- Chromosomal changes: parts
- chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes
Cytological detection of translocations
- size may change
- banding patterns switched
- centromere location may change
Adjacent-1 Segregations
Up: T1 + N2
Down N1 + T2
-often inviable
Alternate Segregations
Up: T1 + T2
Down: N1 + N2
-viable
Monosomics
- 2n - 1
- human examples only involve the Y chromosome, all other are lethal
Turner’s Syndrome
- Monosomic (2n - 1)
- XO
- Female w/o barr bodies
Trisomics
- 2n + 1
- 47 instead of 46 in humans
Kleinfelter’s syndrome
- Trisomic (2n + 1)
- XXY
- Male w/ barr bodies
No syndrome
- Trisomic (2n + 1)
- XXX
- XYY
Down’s Syndrome
- Trisomic (2n + 1)
- autosomal; copy of 21st chromosome
Where does aneuploidy originate?
- Failure of homolog or chromatid segregation during meiosis
- Nondisjunction
Nondisjuction
- Chromosomal Changes: aneuploidy
- results in daughter cells with abnormal chromosome numbers (aneuploidy)
- Failure to separate during either Meiosis I, Meiosis II or Mitosis
Polyploidy
- More than 2 chromosome sets
- failure of the spindle during mitosis
- 2n to 4n
Autopolyploidy
- Chromosomal Changes: polyploidy
- extra sets of chromosomes from the same original species via somatic doubling
Allopolyploidy
- Chromosomal Changes: polyploidy
- extra sets of chromosomes from different but related species
- 2n(1)+2n(2)
Sterile cross-hybrid to fertile derivative
- n+n = 15 (odd # = sterile)
- somatic doubling occurs
- fertile derivative!
- 2n+2n = 30
