Chromosomes and Chromosomal Abnormalities - Genetics 2 Flashcards
How is a chromosome recognised?
- Banding pattern with specific stains
- Length
- Position of the centromere
What can the short arm of the chromosome be written as?
p
What can the long arm of the chromosome be written as?
q
What is an afrocentric chromosome?
- Doesn’t really have a short arm (little bit that encodes satellite ribosomal genes, tRNAs etc)
- Has a centromere and a long arm
- Only chromosomes 13, 14, 15, 21 and 22
What is a balanced chromosomal rearrangement?
• All chromosomal material is present
What is an unbalanced chromosomal rearrangement?
- Extra or missing chromosomal material, usually one or three copies of the same gene
- Developmentally ‘bad news’
What is aneuploidy
When there is a whole extra or missing chromosome
What is Translocation?
Rearrangement of chromosomes
What is Aneuploidy usually caused by?
Nondisjunction in meiosis in either meiosis 1 (resulting in two gametes having 3 chromosomes and two having one) or in meiosis 2 (resulting in two gametes being normal and one having 3 and the final having only one)
What is Down syndrome?
Trisomy 21 (3 copies of chromosome 21)
What is Edward syndrome?
Trisomy 18
What is Patau syndrome?
Trisomy 13
How can chromosomal defects be tested before birth?
- Interphase chromosome counting using FISH (fluorescence In situ Hybridization)
- Chromosome will fluoresce and then can be counted, for example: a trisomy will show 3 fluorescent chromosomes instead of 2
How can chromosomal defects be tested (not before birth)
Array CGH (comparative genome hybridisation)
• Patient DNA and Control DNA of an equal amount and normal chromosome complement are mixed
• Hybridise them into a gene chip and if the control DNA and the patients DNA match, it should produce an even graph with equal amounts of the control and patient DNa
• If there is less or more of the patient DNA/chromosome this will be shown as a slight dip or a peak in the graph
What is Turner syndrome?
45X: only one sex chromosome