Chromosomal abnormalities

Chromosomal Abnormalities

Can be numerical or structural

Numerical: having too many or too few chromosomes

Structural rearrangement

Autosomes

Monosomy and Trisomy

Body cant tolerate really Monosomies

Polyploidy

Extra set of chromosomes

All numbers not multiples of N

Usually lethal in embryos

Aneuploidy

Abnormal number of chromosomes

Tetraploidy (4n)

Four full sets of chromosomes

Lethal in humans

Common Autosomal Aneuploidies

Down Syndrome 47, +21

Edwards Syndrome 47, +18

Patau Syndrome 47, +13

Sex Chromosome Aneuploidies

Turner Syndrome 45, X

Klinefelter Syndrome 47, XXY

Triple X Syndrome 47, XXX

XYY Syndrome 47, XYY

Translocations

Interchange between chromosome arms

Reciprocal Translocation

Exchange of chromosomal segments in both directions

It can be a combination or Dicentic and acentic fragment

Non reciprocal translocation

Only one chromosome puts a segment in another

Robertsonian Translocations

Long arm goes with long arm and short arm goes with short arm

ONLY acrocentric chromosomes

Short arms are lost usually

13, 14, 15, 21, 22

Alternate segregations

Offspring chromosomally normal or have a balanced translocation with normal phenotype

Adjacent segregation

gametes are unbalanced and offspring may have trisomy or monosomy

Deletion

Portion of chromosome is deleted

Cru chat- partial deletion chromosome 5

Terminal deletion

Single break that includes chromosome tip

Interstitial deletion

Two breaks occur and material between break is lost

Duplication

Same region of chromosome will be twice

Prader willi- duplication in chromosome 15

Non disjunction

Failure of chromosomes to disjoin normally durning meiosis/mitosis

Ring chromosome

Very common in down syndrome

Deletion in both tips of chromosomes so the ends fuse

Inversions

Portion of chromosome is broken, turned upside down and reattached (material is inverted)

Paracentric inversion

Centromere is not included

Pericentric inversion

Centromere is included