Lecture 15 Flashcards
Define aneuploidy
An abnormal number of a particular chromosome
How does Down syndrome trisomy 21 occur?
It comes from an individual getting 3 copies of chromosome 21
What can the frequency of Down syndrome depend on?
The mothers ages
What is nondisjunction?
Failure of chromosomes to seperate properly during meiosis
What happens to the gametes when there is non disjunction during meiosis I?
N+1, N+1, N-1, N-1.
What happens to the gametes when there is nondisjunction during meiosis II?
N+1, N-1, N, N
What is Klinefelter syndrome?
XXY genotype
Phenotypically male but with female features
What is turners syndrome?
When there is only one X chromosome and nothing else.
Phenotypically female
What does the phenotype of an individual with Turner syndrome depend on?
Whether the X chromosome came from Mum or Dad
Define polyploidy
Possession of multiple sets of chromosomes
How do organisms become polyploid?
It occurs when a rare mitotic or meiotic catastrophe causes the formation of gametes that have complete set of duplicate chromosomes.
What is deletion? (Chromosomes)
Where a chromosomal segment is removed
What is duplication? (Chromosomes)
When a segment is repeated
What is inversion? (Chromosomes)
When a segment is reversed
What is translocation? (Chromosomes)
When a segment from one chromosome is moved to a nonhomologous chromosome
What is lejeune syndrome (cri du chat)?
Lejuene syndrome occurs when there is a deletion of the short arm of chromosome 5. Effects: Severe intellectual syndrome Can’t speak properly Die as children
What is the result of meiosis in a human inversion heterozygote?
Shortened arm on one chromosome and lengthened arm of other chromosome.
Reduced fertility but not completely sterile
What do 95% of patients with chronic myeloid leukaemia have?
Philadelphia translocation t(9;22)
What does Philadelphia translocation cause?
TK over-expression because the gene can’t be regulated.
Treatable with gleevac in 90% cases
What is robertsonian translocation?
Centric fusion
What is familial Down syndrome?
Occurs from t(14;21), Down syndrome that runs in families
