Cytogenetics Flashcards

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1
Q

Metacentric chromosome

A

Centromere is in the middle p=q

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2
Q

Submetacentric chromosome

A

Off-center centromere

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3
Q

Acrocentric chromosome

A

Centromere near the end (ends are called “satellite DNA” on p arm

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4
Q

Short arm

A

p

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5
Q

Long arm

A

q

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6
Q

What is euploidy?

A

abnormal number of copies of all chromosomes

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7
Q

What is triploidy?

A

3n
- usually SAB in 1st trimester
- 17% of SABs
- Usually 2 sperm cells fertilize 1 egg

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8
Q

What is tetraploidy?

A

4n
few cases, nonviable
1-2% of SABs
Possible due to failure of cells to cleave during division

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9
Q

What is the incidence of Down Syndrome?

A

1 in 185 births

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10
Q

What causes Down Syndrome?

A

95% T21 (90% maternal meiosis I, 10% paternal meiosis II)
4% Robertsomian translocation
Usually with 14 or 22
Rare: 21q21q translocation - isochromosome
Rare: partial T21 (part of q arm)
Rare: mosaic T21

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11
Q

What are the psuedoautosomal regions on the X and Y chromosomes?

A

Regions on X and Y that exhibit autosomal inheritance
Site of recombination - failure can lead to nondisjunction

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12
Q

What is uniparental disomy (UPD), and what types are there?

A

Both chromosomes from the same parent

Isodisomy: Chromosomes are identical and inherited from sister chromatids
Heterodisomy: inheritance of both homologs from one parent

This often happens from trisomy rescue

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13
Q

What is a marker chromosome? What are the most common types?

A

small chromosomes in addition to the normal amount

Extra chromosome 15
Ring chromosomes - marker chromosome with no telomeres (usually mosaic)

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14
Q

What is an isochromosome?

A

one arm is duplicated → mirrored chromosome
Opposite arm may be deleted
Trisomy of duplicated arm, monosomy of deleted arm

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15
Q

What is a Robertsonian translocation?

A

Most common rearrangement in humans
Fusion of two acrocentric chromosomes near the centromere
Loss of short arms is fine - little genetic material

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16
Q

What is an inversion, and what types are there?

A

two breaks in a single chromosomes and the segment flips

Paracentric - includes only one arm
Pericentric - includes both arms (and centromere)
Balanced - usually no phenotype in carriers

17
Q

What is allelic heterogeneity?

A

different mutations in a gene → same phenotype

18
Q

What is locus heterogeneity?

A

mutations in different genes → same phenotype