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Genetics > Module A: Cytogenetics > Flashcards

Module A: Cytogenetics Flashcards

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1
Q

What is chromatin?

A

complexes of chromosomes condensed with histones

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2
Q

Describe the utility of a standard karyotype and how it is obtained.

A

how it is obtained:

cells are induced to divide, then trapped in metaphase and stained

utility:

allows chromosomes to be visualized under a light microscope

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3
Q

Only certain cells can be induced to divide for a standard karyotype. What are they? (6)

A

blood lymphocytes

amniotic fluid cells

chorionic villi

skin fibroblasts

testicular biopsies

bone marrow

[BACSTB]

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4
Q

In the absence of genes on a Y chromosome, how will the embryo develop?

A

embryo will develop into a female

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5
Q

In the context of chromosome staining, what are bands?

A

predictable patterns of light and dark regions

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6
Q

A typical chromosome spread has how many bands?

A

550 bands

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7
Q

High resolution chromosome spreads have how many bands?

A

1500 bands

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8
Q

Define acrocentric chromosome.

A

centromeres close to one end

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9
Q

Define metacentric chromosome.

A

centromeres near middle

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10
Q

Define centromere.

A

constriction points where spindle fibers ttach

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11
Q

Define autosome.

A

chromosomes that are not sex chromosomes

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12
Q

Define euchromatin.

A

contains genes being actively transcribed

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13
Q

Define heterochromatin.

A

condensed and generally inactive

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14
Q

What are homologous chromosomes?

A

two chromosomes in a pair in diploid organisms

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15
Q

What are satellites?

A

strings of repetitive DNA (usually rRNA coding) that make up short arms of acrocentric chromosomes

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16
Q

What are telomeres?

A

strings of repetitive DNA at ends of chromosomes

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17
Q

Human chromosomes are numbered from 1 to 22 in what order?

A

roughly in size order

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18
Q

Describe how the centromere divides the chromosome.

A

centromere divides chromosome into short arm (p) and long arm (q)

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19
Q

Describe the band-numbering convention in chromosomes. (4)

A

bands are numbered extending from centromere (band 10)

first major band = 1, second major band = 2, etc.

subbands of major band given second digit (i.e. third subband of first band = 13)

splitting of subband denoted by number following decimal point

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20
Q

In the standard nomenclature system, how are abnormalities indicated? Give an example by writing out the karyotype nomenclature for a male with Down syndrome. (2)

A

abnormalities indicated following comma after sex chromosomes

47, XY, +21

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21
Q

In the standard nomenclature system, how are deletions indicated? Give an example by writing out the karyotype nomenclature for a male with a deletion of the short arm of chromosome 5. (2)

A

indicated with “del”

46, XY, del(5p)

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22
Q

In the standard nomenclature system, how are duplications indicated?

A

indicated with “dup”

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23
Q

In the standard nomenclature system, how are inversions indicated?

A

indicated with “inv”

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24
Q

Chromosome abnormalities are relatively common in what groups of people?

A

couples with infertility

spontaneous abortions/miscarriages

children with multiple congenital anomalies

couples with multiple miscarriages

individuals with cancer

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25
Q

Define aneuploidy.

A

having abnormal number of chromosomes

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26
Q

Define trisomy.

A

having three copies of a chromosome

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27
Q

Define triploidy.

A

having three copies of all the chromosomes

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28
Q

Define monosomy and its clinical relevance. (2)

A

having only one copy of a chromosome

other than X-monosomy, most monosomies are lethal in humans

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29
Q

Define inversion.

A

chromosomal anomaly in which part of chromosome is turned around in orientation

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30
Q

Define translocation.

A

anomaly in which part of one chromosome is attached to another (usually reciprocal)

31
Q

Define Robertsonian translocation.

A

attachment of long arms of 2 acrocentric chromosomes at centromere

32
Q

What is the karyotypic nomenclature for Down syndrome?

A

47, XX (or XY), +21

33
Q

What is the karyotypic nomenclature for Kleinfelter syndrome?

A

47, XXY, +X

34
Q

What is the karyotypic nomenclature for Turner syndrome?

A

45, X

35
Q

Numerical chromosomal abnormalities include (2)

A

errors of ploidy = multiples of 23 chromosomes other than 2

aneuploidy = extra or missing copies of a single/multiple chromosomes, but not the whole set

36
Q

Structural chromosomal abnormalities include (5)

A

reciprocal translocations

Robertsonian translocations

deletions

duplications

inversions

37
Q

What are copy number variants?

A

common occurrences of duplications and deletions too small to be seen by standard karyotype analysis

38
Q

Under what conditions is a chromosome rearrangement called “balanced?”

A

if there is no missing or extra DNA

39
Q

Broadly speaking, what are the clinical presentations of someone with a balanced rearrangement?

A

person should be generally normal, but may be at risk for having children with unbalanced chromosomal rearrangements

40
Q

In mitosis, what structures behave independently of each other?

A

in mitosis, the pairs of chromosomes (not the chromatids) behave independently of each other

41
Q

What happens in meiosis I? (3)

A

two pairs of chromosomes (each with 2 sister chromatids) pair as bivalents

then homologous regions of the 2 chromosomes pair precisely and cross over

spindle fibers pull bivalents apart, resulting in 2 daughter cells w/ 23 chromosomes (46 chromatids) in each

42
Q

What is non-disjunction?

A

failure of chromosomes or chromatids to segregate properly, resulting in aneuploidy

43
Q

What is mosaicism and how does it develop? (2)

A

a phenomenon in which some cells have an aberrant genotype, but then other cells within the same individual have a normal genotype

always a post-zygotic event

44
Q

What is hybridization?

A

allowing the two strands of DNA to separate, then allowing a matching sequence to bind/anneal to the strand

45
Q

What is stringency?

A

how well the sequences must match for a probe to anneal to a DNA strand, dependent on physical and chemical conditions

46
Q

Describe the properties of short probes. (2)

A

15-60 nucleotides

requires sufficiently stringent conditions

47
Q

Describe the properties of longer probes. (2)

A

~1000 nucleotides

less stringent conditions

48
Q

Describe the mechanism of Dot blots. (2)

A

labeled oligonucleotide hybridizes to patient’s DNA

unbound DNA washed off

49
Q

Dot blots are useful for what purpose?

A

detecting specific single base changes

50
Q

Describe the mechanism of Southern blots.

A

detect the size of a DNA fragment, sometimes produced by cutting DNA w/ restriction endonuclease, that binds to a probe

51
Q

In what context are Southern blots useful?

A

used to detect the number of sequence repeats in a gene

52
Q

FISH stands for

A

fluorescence in situ hybridization

53
Q

FISH is used for (2)

A

determining whether a segment of DNA is present on a chromosome

detecting microdeletions or duplications in patient’s DNA

54
Q

Describe how FISH is performed. (3)

A

mitotic chromosome spread placed on slide (just like conventional karyotype)

probe hybridized to slide and excess washed away

fluorescence microscope reveals signal (dot) where probe has hybridized

55
Q

In what range can FISH detect deletions?

A

FISH is used to detect deletions in the 40 kb to 1 Mb range

56
Q

FISH is NOT useful for what kinds of changes? (2)

A

single base changes

small deletions

57
Q

Why would interphase FISH be helpful compared to metaphase FISH or conventional karyotypes? (2)

A

helpful because cells do not need to be induced to divide

study can be done more rapidly than conventional karyotype or metaphase FISH

58
Q

Describe the process of interphase FISH. (4)

A

cells bound to microscope slide

probe allowed to hybridize

unbound probe washed away

number of signals (dots) in each nucleus indicates number of DNA sequences

59
Q

What does CMA stand for?

A

chromosome microarray

60
Q

What are the two types of cytogenomic microarray (CMA) analysis?

A

array comparitive genomic hybridization (aCGH)

in silico methods

61
Q

What is a common feature of the two types of CMA analysis?

A

both use thousands of probes bound to a silicon chip in an array

62
Q

Explain the general basis of comparitive genomic hybridization. (5)

A

patient + control DNA labeled with different fluorescent probes and mixed

mixture of DNA hybridized to chip with thousands of single copy sequences

washing

if patient DNA has more copies than control DNA, probe will fluoresce with patient color

if patient DNA has fewer copies than control DNA, probe will fluoresce with control color

63
Q

Typical CMA arrays can detect what size of copy number variants?

A

20kb or more in size (though more specialized arrays that detect smaller variants do exist)

64
Q

In CMA analysis, a 1:2 ratio for an autosomal probe indicates

A

patient has a deletion

65
Q

In CMA analysis, a 3:2 ratio for an autosomal probe indicates

A

patient has a duplication

66
Q

What are single nucleotide polymorphisms (SNPs)?

A

DNA sequence variations among chromosomes in the population

67
Q

Describe how SNP-CMA analysis differs from standard aCGH CMA analysis.

A

patient’s DNA is labeled with a fluorescent probe and washed and all, but this technique does not require control DNA

68
Q

How is the readout of SNP-CMA analysis interpreted?

A

intensity of bound fluorescence indicates whether 0, 1, 2 or more sequences from the patient bind to the particular probe

69
Q

CMA analysis can detect (2)

A

genetic imbalances

copy number variants

70
Q

CMA analysis can NOT detect

A

balanced rearrangements

71
Q

What is the resolution for conventional karyotyping?

A

3-5 Mb

72
Q

What is the resolution for FISH?

A

100 kb - 1000 kb

73
Q

What is the resolution for CMA?

A

5-30 kb

74
Q

What is the resolution for ASO?

A

single base differences (but only specific sequence variants)

Genetics (5 decks)

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