LECTURE 3 (the molecular basis of mutation 3) Flashcards
(39 cards)
What’s deletion?
The loss of base pairs in a gene or a part of a chromosome.
What does a chromosome deletion involves?
It involves the cut of a region that’s not the centromere otherwise it couldn’t be pulled in the chromosomal spindle and it’ll be lost.
What are the two main types of deletions?
Intragenic and multigenic.
describe intragenic deletions
It’s located w/in the gene, it deactivates it and produces a null mutation (the gene won’t be expressed e.g albinism
describe multigenic deletion
not only one gene is missing but several. serious consequences. appears as a result of inbreeding leaving homozygous. can uncover recessive alleles
How can we correct intragenic deletions to the wild type?
it’s impossible, only base pair mutations not involving deletions can be corrected.
How can we detect deletions?
via chromosome mapping, having a look under the microscope and determining the position of the deletion loop or if a recessive allele is expressed (shows dominance) in a heterozygous that implies a deletion
what does the uncovering of recessive alleles imply?
A deletion.
Give two examples of deletions in humans
- Cri du Chat. occurs a the tip of the p arm of chr 5. moonlight face, mental retardation, reach adulthood.
- williams syndrome 1.5Mb deleted in the chr 7 musical abilities, caused by unequal crossover probably
What is pseudo dominance?
When a recessive allele is expressed and so it appears to have dominance
How can we use pseudo dominance to map deletions?
if the deletion location is known pseudo dominance can be used in reverse so we can asses the position of the mutant alleles.
What are duplications?
extra copies of chromosome regions.
What types of duplications can we encounter?
Tandem duplications and insetional duplications
What are tandem duplications?
two identical DNA seq or chr region e.g an extra cur arm or part of the arm attached to a non-homologous chr. They can’t unmask recessive alleles.
What are insertional duplications?
identical DNA seq that are in different section of a chr or even in different chr. they’re essential for evolution bc they get accumulated over several generations.
How can we use microarrays to quantify deletions and duplications?
The DNA of wild type and of mutant are dyed with different fluorescent dyes that emit different wavelength. this are added to cDNA clones and will hybridize and we can compare the abnormal wavelengths to the normal chr one to quantify these types of mutations.
What are transposable elements?
DNA elements that move to new positions in the chr or in a different chr
How are T.E detected?
Through mutations because when they’re inserted they deactivate genes. they have effect on genes if they’re located in the middle of a coding seq.
Which % of human chr are T.E ?
50%
How many classes of T.E are there?
class 1 and class 2
What are T.E class one?
they’re retroelements bc they have an RNA intermediate this RNA intermediate makes the insertion to be permanent
What are class 2 T.E?
they’re simple DNA elements. they were discovered in maize
How are transposons called in euk? What structure do they show?
Bacterial insertion sequences. (IS) They always interrupt a gene inactivating the gene expression. Firstly found in gal operon in E.coli
(IR) abcd transposase dcba (IR)
How many types of bacterial transposons can we find?
- composites
- simple
