L19: Numerical Chromosome anomalies Flashcards
What are the main types of mutation
- single gene disorders : autosomal dominant and recessive and x linked
- Chromosome
- mitochondrial
- multifactorial
What is the classification of chromosomal anomalies
- numerical
- structural
- cell lines
What does numerical chromosomal anomalies include
- aneuploidy: trisomy and monosomy
- polyploidy: trisomy
What does structural chromosomal anomalies include
- translocation: reciprocal and robertsonian
- deletion
- duplication
- inversion
What does cell lines include
Mosaicism
What is the most common numerical disorders
Down’s syndrome Patau syndrome Edwards syndrome Klinefelter syndrome Turner syndrome
What are the 3 clauses of Down’s syndrome
- trisomy 21
- robertsonian translocation
- somatic mosaicism
How does trisomy 21 occur to give Down syndrome
- non disjunction occurs in meiosis 1 or 2 in eggs of the mother
Why does non disjunction occur in eggs but not sperms to give trisomy 21
- oocytes are a stock of egg
- each month one oocyte is released and completes meiosis 1
- as the maternal age increases the egg undergoes wear and tear to the spindle fibres
- at fertilisation when meiosis 2 is occurring the spindles cannot separate the chromosomes
- this results in trisomy 21
What is patau syndrome
Trisomy 13
What is edwards syndrome
Trisomy 18
What is Klinefelter syndrome
47, XXY
What is turners syndrome
45,X
What is triploidy
When there are 69 chromosomes
Is autosomal monosomy or sex chromosome anamolies the worst
Autosomal monosomy
Why does an extra chromosome of 21 give downs syndromes phenotype
- 1.5x gene dosage
- overall effect on imbalance of development
How do we recognise sequences experimentally
By DNA hybridisation
- make a fluorescent probe that recognises short sequence we want
- when it binds to the short sequence the colour is given off and seen
What is FISH
- A fluorescent probe recognises a gene on of the chromosome
- the number of chromosome can be seen in one cell
What would we see by FISH for a patient who has Down syndrome
- 3 same colours of chromosome 21
What is array CGH
- identifies specific genes on a chromosome
