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GENE 418: Human Genetics > Structural and numerical chromosome abnormalities > Flashcards

Structural and numerical chromosome abnormalities Flashcards

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1
Q

What are unbalanced abnormalities?

A

Result in a gain or loss of genetic information

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2
Q

What are the 6 types of unbalanced structural chromosome abnormalities?

A
  1. Deletions
  2. Duplications
  3. Ring chromosomes
  4. Isochromosomes
  5. Dicentric and acentric chromosomes
  6. Non-reciprocal translocations
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3
Q

What are balanced chromosome abnormalities?

A

Not the typical configuration of where the material should be, but not missing anything or have anything extra

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4
Q

What are the 3 types of unbalanced structural chromosome abnormalities?

A
  1. Inversions
  2. Reciprocal translocations
  3. Robertsonian translocations
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5
Q

What is the result of a deletion in terms of the amount of genetic material?

A

Partial monosomy and haploinsufficiency for the genes involved

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6
Q

Would we start with FISH when trying to find a chromosome abnormality?

A

No, need to know what we’re looking for. Will start with G-banding and then probe from there

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7
Q

Why do we counterstain chromosomes when doing cytogenetic analysis?

A

So we can actually tell how many nuclei we’re looking at. Otherwise the results would be difficult to interpret.

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8
Q

What do deletions look like with FISH hybridization?

A

Only one signal of the corresponding sequence is seen

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9
Q

What is the result of a duplication in terms of the amount of genetic material?

A

Partial trisomy

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10
Q

What do duplications look like with FISH hybridization?

A

An extra signal of the corresponding sequence is seen

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11
Q

What are ring chromosomes?

A

Chromosomes that lost their telomeres and subtelomeric sequences and circularized

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12
Q

How do we identify which chromosome formed a ring chromosome?

A

Banding pattern

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13
Q

Why is identifying the origin of a ring chromosome sometimes hard?

A

Often don’t get much more than a centromere and pericentric heterochromatin, so need FISH to figure it out

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14
Q

What are isochromosomes?

A

Chromosomes formed when the plane of segregation is perpendicular to what should’ve normally happened. They have 2 p arms or 2 q arms

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15
Q

What is the result of an isochromosome in terms of the amount of genetic material?

A

Partial monosomies for the lost arm and partial trisomies for the arm that’s still there

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16
Q

What do isochromosomes look like with FISH hybridization?

A

Arms are mirror images of each other

17
Q

What are dicentric chromosomes?

A

Chromosomes with 2 centromeres, get torn apart during meiosis because of spindles pulling on them both

18
Q

What are acentric chromosomes?

A

Chromosomes with no centromere. Get lost during metaphase since there’s nothing for the spindles to attach to

19
Q

What do inversions look like with FISH hybridization?

A

If we have several probes that bind sequentially next to each other, they’ll be in a different order

20
Q

What do translocations look like with FISH hybridization?

A

Sequences that are supposed to be on one chromosome will hybridize with markers for a different chromosome

21
Q

What is an aneuploidy?

A

Missing or having extra sets of one chromosome, where the total number of chromosomes is not a multiple of the haploid number 23

22
Q

What is mixoploidy?

A

A generic term for cells derived from 2 or more distinct cell lineages

23
Q

What are the 2 types of mixoploidy?

A

Mosaicism and chimerism

24
Q

Will constitutional triploid individuals survive?

A

Yes, but perinatal death is typical

25
Q

What are the 3 mechanisms by which a triploid individual can be generated? Which is the most common?

A
  1. Dispermy - two haploid sperm fertilize a haploid egg
  2. Haploid sperm fertilizes diploid egg
  3. Diploid sperm fertilizes haploid egg

Dispermy most common

26
Q

How do we know if the extra set of chromosomes in a triploid individual came from mom or dad?

A

If it came from dad, see placental abnormalities. If it came from mom, see spontaneous early abortions

27
Q

How do tetraploid individuals arise?

A

Endoreduplication in the early zygote. DNA copies but cell division doesn’t happen

28
Q

Is tetraploidy always lethal?

A

Constitutive tetraploidy is, yes. Segmental tetraploidy is quite common though

29
Q

What are two ways for aneuploidies to happen?

A

Non-disjunction and anaphase lag

30
Q

What does the trisomic chromosome look like when non-disjunction occurred in meiosis I?

A

The homologs didn’t separate, so the trisomic gamete gets a sister chromatid from each one. Can see 3 different alleles

31
Q

What does the trisomic chromosome look like when non-disjunction occurred in meiosis II?

A

The sister chromatids didn’t separate, so the trisomic gamete gets the same allele twice. Can’t see multiple alleles

GENE 418: Human Genetics (31 decks)

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