Inversions & Insertions Inheritance Flashcards
What are the 2 types of inversions and what do they mean?
Pericentric - includes the centromere, changes the shape of the chromosome.
Paracentric - confined to either the p or q arm of the chromosome, doesn’t include the centromere.
How does an inversion behave at meiosis?
- attempts to achieve maximum pairing
- if the inversion is big the main segment will pair and the small ends will mismatch
- or it forms an inversion loop
What causes the potential imbalance when an inversion is involved?
A uneven number of crossovers within the inverted segment.
What are the resulting products if you get an uneven number of crossovers within a PERICENTRIC inverted segment?
1 x normal chromatid
1 x inverted chromatid
2 recombinant del/dup chromatids - each one will have a duplication of one end that lies outside of the inversion and a deletion of the other end that lies outside of the inversion.
Which carries a higher risk: a small pericentric inversion or a large one? Why?
The large one.
The risk of an abnormal liveborn is higher when the areas outside of the inversion are small (large inversion, non-inverted segment small). This can result in an fetus with a relatively small duplication and deletion which may be compatible with life with an abnormal phenotype.
Smaller inversions are more likely to produce a large imbalance which isn’t compatible with life.
If you analysed an array and saw a chromosome with a deletion at one end and a duplication at the other, what would you think?
Could be the recombinant product of an inversion.
What are the resulting products if you get an uneven number of crossovers within a PARACENTRIC inverted segment?
1 x normal chromatid
1 x inverted chromatid
2 x recombinant chromatids - 1 of which will be dicentric and 1 will be acentric.
What are the different types of insertions?
Inter or intra-chromosomal and segment can be direct or inverted.
How do insertions behave at meiosis?
Interchromosomal
- small ones likely to loop out
- larger ones a quadrivalent will form and recombination can form deletion and duplication products.
Intrachromosomal
- small ones may loop out
- larger ones will result in complex looping back and forth! This can produce complicated recombinaton products.
What is the risk of a carrier with a balanced insertion?
Very high!
But ultimately depends on the viability of the resulting duplication or deletion.
Intrachromosomal - 15%
Interchromasomal - 50% of either the del or the dup being passed on (50% of being either a carrier or normal).
Why are insertions and inversions relevant in recurrent miscarriage and infertility?
Miscarriage:
Unbalanced products from incorrect segregation or recombination may cause an imbalance that will allow pregnancy but will abort part way through.
Infertility:
Spermatogenesis is very fussy!
If the rearrangement fails to pair correctly it can interfere with the X-Y bivalent, when this occurs spermatogenesis is blocked. The more often it occurs, the greater the impact on sperm count.
