Genetics: From Whole Chromosomes to Single Bases Flashcards
how is a chromosome recognised
- centromere position
- length
- banding patters with specific stains
what is the make up of a chromosome
- telomeres at either end
- centromere
- short arm (p)
- long arm (q)
what are acrocentric chromosomes and what are they liable to
- chromosomes that can lose their short arm without consequences for that individual
- translocations
aneuploidy
whole extra/missing chromosome
balanced translocation/re-arrangement
all genetic material is present
unbalanced translocation/re-arrangement
genetic material is missing or extra (1/3 copies)
what is a robertsonian translocation and what does it pose a risk of
- two acrocentric chromosomes stuck end-to-end, translocation
- risk of trisomy in offspring
why is X-chromosome aneuploidy better tolerated
X-chromosome inactivation
what do unbalanced translocations result in in pregnancy
- miscarriage
- dysmorphic delayed child
FISH
fluoresent in-situ hybridisation
what does FISH detect
chromosomal abnormalities
how does FISH work
- maps all the genetic material in a cell and targets a specific sequence
- flurescent markers are attached to this sequence and you are now able to see if its present
what does an aCGH detect
detects deletions/duplications - any size imabalance but not balanced translocations
how do an aCGH work
takes the entire genome and compares it to a reference sample
what indicates deletions in aCGH
half as much DNA on the graph compared to reference
what is 1st line chromosome testing
aCGH
what does karyotyping detect
any change in chromosomes - un/balanced
how does PCR testing work
sequence a small section of DNA many times - useful to sequence tiny changes but need to know which stretch to sequence
how does NGS work
used instead of PCR
- can sequence the whole genome or just exons and is used to show differences between the normal and whats sequenced
mocaicism
different cells having a different genetic makeup (chromosomal or point)
somatic mocaicism
changes in DNA that are not inherited but happen during proliferation
partial trisomy
an extra ‘chunk’ of chromosome as a result of parental balanced translocation
what is a homologous chromosome
the same chromosome repeated (i.e. during mitosis) - same centromere position, length and band sequence
