21 & 22- Chromosome Abnormalities 1 & 2 Flashcards
Three types of chromosome mutations
- Chromosome rearrangements: alter the structure of chromosome
- aneuploid: number of chromosomes is altered (one or more individual chromosome added or deleted)
- Polyploid: one or more complete sets of chromosomes are added
4 types of chromosome rearrangements
Duplications, Deletions, Inversions and translocations
Effect of duplication mutation
Problems arise in chromosome pairing during meiosis. Duplicated chromosome loops out to allow sequences to aline
Cri-du-chat syndrome
- Heterozygous deletion of tip of p arm
- Chromosome 5
- Small head, distinctive cry, widely spaced eyes, round face, retard
Wolf Hirschhorn syndrome
- Deletion
- 4, short arm
- Small head with high forehead, wide nose, cleft lip and palate, severe retard
Williams-Beuren syndrome
- Deletion
- 7, long arm
- Facial features, heart defects, mental impairment
Prader Willi syndrome
- Deletion
- 15, long arm
- Feeding difficulty early age but obese after 1 year, mild to moderate retard
Types of aneuploidy
- Nullisomy: loss of both members of homologous sets of chromosomes
- Monosomy: loss of a single chromosome (45 chr, 2n-1)
- Trisomy: gain of single chromosome (47 chr, 2n + )
- Tetrasomy: gain of two homologous chromosomes. (48 chr, 2n + 2)
what causes extreme abnormalities in monosomics
The expression of any deleterious recessive alleles on the monosomic chromosome
Aneuploidy
Aneuploidy is a change in the number of individual chromosomes but NOT by a complete set of chromosomes.
What causes aneuploidy
Nondisjunction, where chromosomes fail to correctly
separate (segregate) during meiosis. This can occur at 1st or 2nd meiotic division.
Polyploidy
Change in number of chromosome sets
Types of polyploidy
- Diploid (2n): two complete sets of chromosomes
- Triploid (3n): extra set of chromosomes (69 in total)
- Tetraploid (4n): 4 complete sets of chromosomes (92)
