Santolaya - Meiosis and Chromosomal normalities Flashcards
Non-disjunction during meiosis 1
Two zygotes will have two pairs of the same chromosome from different parents. Two zygotes will have 0 pairs of the chromosome
Non-disjunction during meiosis 2
Will cause 2 of the offspring to have 1 chromosome. One zygote will have zero chromosomes. One zygote will have two pairs of the chromosome from the same parent
Turner syndrome
45, X
How do we test to see if the non-disjunction event occurred in meiosis 1 or meiosis 2?
You look at the DNA close to the centromere (they are called Polymorphic DNA markers, which are CA repeats). This way you can tell if you have two pairs of the chromosome from same parent or different parents. The reason we look near the centromere is because there is crossing over at the metaphase plate normally.
Translocations
- They raise the risk of non-disjunction because the translocated chromosomes might not synapse properly from the metaphase plate.
- Can be reciprocal or non-reciprocal
- Recombination at the inversion loop during M-1 can cause acentric/dicentric chromatids and duplication/deficiencies of genetic material.
Mary Lyon Hypothesis (X-inactivation)
In a female, her body will preferentially turn off the X that has a deletion in it.
Uniparental Dysomy
If you have a nondisjunction during meiosis 2 and you have 2 chromosomes from the same parent, when that gets fertilized, you now have 2 chromosomes from one parent and one from the other. You can have random trisomy rescue where one chromosome disappears. If it is the other parents chromosome then you have only 2 chromosomes from the same parent. This causes all sorts of weird inheritance patterns like
Second trimester “quad” screening test
Looks at certain proteins and the ratio of your protein levels to normal protein levels.
Centromere Index
length of p arm / total length of chromosome x 100
