1. Lecture 40
Prof Duncan Shaw

2. Chromosome abnormalities
Numerical abnormalities - gain or loss of one or more whole chromosome(s)
Includes aneuploidy (trisomy, monosomy)
Structural abnormalities - chromosome breakage and rejoining in a different configuration
Includes translocations, deletions, inversions
Only a few are compatible with life

3. Aneuploidies

4. The cause of aneuploidy
Non-disjunction - failure of pairs of chromosomes to separate during meiosis I or II
Probably usually due to ageing of oocyte, hence maternal age effect
Environmental factors may also be important, e.g. radiation

7. Structural abnormalities
Translocation - transfer of part of one chromosome to another
Reciprocal translocation
Robertsonian translocation
Deletions - loss of material from within a chromosome (usually lethal)
Insertions - extra material added within a chromosome
Inversion - section within a chromosome is turned around