Structural and numerical chromosome abnormalities Flashcards
What are unbalanced abnormalities?
Result in a gain or loss of genetic information
What are the 6 types of unbalanced structural chromosome abnormalities?
- Deletions
- Duplications
- Ring chromosomes
- Isochromosomes
- Dicentric and acentric chromosomes
- Non-reciprocal translocations
What are balanced chromosome abnormalities?
Not the typical configuration of where the material should be, but not missing anything or have anything extra
What are the 3 types of unbalanced structural chromosome abnormalities?
- Inversions
- Reciprocal translocations
- Robertsonian translocations
What is the result of a deletion in terms of the amount of genetic material?
Partial monosomy and haploinsufficiency for the genes involved
Would we start with FISH when trying to find a chromosome abnormality?
No, need to know what we’re looking for. Will start with G-banding and then probe from there
Why do we counterstain chromosomes when doing cytogenetic analysis?
So we can actually tell how many nuclei we’re looking at. Otherwise the results would be difficult to interpret.
What do deletions look like with FISH hybridization?
Only one signal of the corresponding sequence is seen
What is the result of a duplication in terms of the amount of genetic material?
Partial trisomy
What do duplications look like with FISH hybridization?
An extra signal of the corresponding sequence is seen
What are ring chromosomes?
Chromosomes that lost their telomeres and subtelomeric sequences and circularized
How do we identify which chromosome formed a ring chromosome?
Banding pattern
Why is identifying the origin of a ring chromosome sometimes hard?
Often don’t get much more than a centromere and pericentric heterochromatin, so need FISH to figure it out
What are isochromosomes?
Chromosomes formed when the plane of segregation is perpendicular to what should’ve normally happened. They have 2 p arms or 2 q arms
What is the result of an isochromosome in terms of the amount of genetic material?
Partial monosomies for the lost arm and partial trisomies for the arm that’s still there
What do isochromosomes look like with FISH hybridization?
Arms are mirror images of each other
What are dicentric chromosomes?
Chromosomes with 2 centromeres, get torn apart during meiosis because of spindles pulling on them both
What are acentric chromosomes?
Chromosomes with no centromere. Get lost during metaphase since there’s nothing for the spindles to attach to
What do inversions look like with FISH hybridization?
If we have several probes that bind sequentially next to each other, they’ll be in a different order
What do translocations look like with FISH hybridization?
Sequences that are supposed to be on one chromosome will hybridize with markers for a different chromosome
What is an aneuploidy?
Missing or having extra sets of one chromosome, where the total number of chromosomes is not a multiple of the haploid number 23
What is mixoploidy?
A generic term for cells derived from 2 or more distinct cell lineages
What are the 2 types of mixoploidy?
Mosaicism and chimerism
Will constitutional triploid individuals survive?
Yes, but perinatal death is typical
What are the 3 mechanisms by which a triploid individual can be generated? Which is the most common?
- Dispermy - two haploid sperm fertilize a haploid egg
- Haploid sperm fertilizes diploid egg
- Diploid sperm fertilizes haploid egg
Dispermy most common
How do we know if the extra set of chromosomes in a triploid individual came from mom or dad?
If it came from dad, see placental abnormalities. If it came from mom, see spontaneous early abortions
How do tetraploid individuals arise?
Endoreduplication in the early zygote. DNA copies but cell division doesn’t happen
Is tetraploidy always lethal?
Constitutive tetraploidy is, yes. Segmental tetraploidy is quite common though
What are two ways for aneuploidies to happen?
Non-disjunction and anaphase lag
What does the trisomic chromosome look like when non-disjunction occurred in meiosis I?
The homologs didn’t separate, so the trisomic gamete gets a sister chromatid from each one. Can see 3 different alleles
What does the trisomic chromosome look like when non-disjunction occurred in meiosis II?
The sister chromatids didn’t separate, so the trisomic gamete gets the same allele twice. Can’t see multiple alleles
