genetic variation from chromosomes and single bases Flashcards
what parts make up a chromosome
telomere, short arm, centromere, long arm
which arm on a chromosome does the most
long arm
what is balanced rearrangement
a chromosome change where all the genetic material is present but maybe a part of a chromosome has stuck onto a different chromosome
what is an unbalanced rearrangement
chromosome change where there is extra or missing chromosomal material. usually 1 - 3 copies of genome. bad news
conventional clinical analysis
currently moving away from looking at chromosomes but understanding conventional cytogenetics is essential
what is aneuploidy
whole extra or missing chromosome
what is translocation
rearrangement of chromosomes
what are insertion/deletion mutations
missing or duplicated material
how does down syndrome come about
unbalanced rearrangement. 47xy + 21 (meaning chromosome 21 has attached to chromosome 47)
what is a robertsonian translocation
they are chromosomal rearrangements that result from fusion of the long arms of two different chromosomes
x chromosome aneuploidy
duplication of the x chromosome. better tolerated because of x inactivation in females
what is reciprocal translocation
when bits of chromosomes swap to other parts. balanced. not important unless on important gene
reproductive risks of reciprocal translocation
50% of conceptions will be normal or have the translocation. if big segments have been swapped the miscarriage can occur. small segments = dysmorphic delayed child
how many base pairs for reciprocal translocations to have an effect
if smaller than 5 million base pairs then you cant see effect or see it on tests
what is the FISH genetic test
fluorescence in situ hybridisation. its a test that looks for gene changes in cells. Makes them glow
what does FISH test for
predominantly breast cancer cells. HER2
what is the aCGH test
used to detect imbalances in genome. DNA based test that reflects underlying chromosomes. can detect imbalance of any size and polymorphisms
what does the aCGH test make things look like
luminescent
where do mutations come from
if one parent has a germ line mutation they can ass it on. if a parent is mosaic the child will be too
what is mosaicism
occurs when a person has two or more genetically different sets of cells in their body. if abnormal outweigh normal then it can lead to disease. it can be chromosomal or point mutation in one gene
somatic mosaicism
all cells suffer mutations as they divide, at meiosis and at mitosis
how to chromosome changes promote cancer
they can activate oncogenes and delete tumour suppressor. eg HER2 can be amplified
how do we analyse DNA: aCGH
for deletions/duplications
how do we analyse DNA: PCR
polymerase chain reaction. allows us to select one small piece of the human genome and amplify it. to compare to normal genomes
