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Cytogenetics > Midterm 1 > Flashcards

Midterm 1 Flashcards

1
Q

% of liveborn babies with chromosomal abnormality?

A

1/120

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2
Q

when was number of chromosomes (46) in cell discovered?

A

1956

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3
Q

nucleosome core

A

147 bp DNA wrapped around 8 histone proteins 2X(H2A,H2B,H3,H4)

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4
Q

centromere makeup

A

satellites: repetitive DNA sequences. Heterochromatin

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5
Q

telomere composition

A

1-2k repeats of TTAGGG. Play role in synapsis

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6
Q

Are telomeric regions gene rich or gene poor?

A

gene rich

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7
Q

telomerase

A

reverse transcriptase that fills in last portion on lagging strand so chromosome does not shorten. Turned off in most adult somatic cells

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8
Q

aging syndromes

A

Hutchinson-Gilford Progeria Syndrome, Werner syndrome, Wiedemann-Rautenstrauch syndrome

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9
Q

nucleolar organizing regions

A

tandem repeats of rRNA genes found in stalk of all acrocentric chromosomes. Forms nucleolus, which combines rRNAs and proteins to form 40S and 60S ribosomal subunits

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10
Q

nucleolus

A

helps transcribe the rRNA genes and ultimately generates the ribosomal subunits (rRNA and proteins)

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11
Q

G-banding bands

A

Giemsa banding. Dark is AT rich (gene poor, heterochromatic) and light is GC rich (gene rich, euchromatic)

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12
Q

two main reagents needed for early chromosome counting

A

colchicine to arrest cells in metaphase, hypotonic solution

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13
Q

first autosomal trisomy to be discovered

A

Down syndrome. 1959

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14
Q

basic steps of preparing a karyotype

A

take blood, culture it, add cholchicine and hyptotonic saline, drop cells on slide, digest with trypsin, stain with Giemsa, analyze

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15
Q

will CGH microarray tell you copy number variants?

A

Yes, you compare to a reference sample and higher or lower expression will tell you

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16
Q

will a microarray detect a balanced translocation?

A

no

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17
Q

solenoid

A

coiling of nucleosomes

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18
Q

metacentric chromosome

A

p and q arms about equal length

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19
Q

submetacentric chromosome

A

small p arm

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20
Q

acrocentric chromosome

A

p arm is just a stalk and satellites (13,14,15,21,22)

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21
Q

composition of centromere

A

kinetochore, tandem repeats called satellite dna (distinct alpha satellites for each chromosome), heterochromatin

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22
Q

teleomere composition

A

role in synapsis- pairing in meiosis begins at subtelomeric regions. High gene density near telomeric regions. 1-2k TTAGGG repeats in telomeres

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23
Q

telomerase

A

reverse transcriptase. Turned off in most adult cells except certain blood cells and gonadal cells

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24
Q

origins of replication

A

sequence varies, but all have high AT content

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25
Q

NORs

A

Stalks of acrocentric chromosomes. Tandem repeats of rRNA genes. Forms nucleolus, which combines rRNA and proteins to make ribosome subunits

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26
Q

what are other types of banding stains?

A

R-banding (Reverse)
C-banding (constitutive heterochromatin)
T-banding (telomere)
Cd staining (centromeric dot or kinetochore)
NOR staining (nucleolar organizing regions)

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27
Q

In g staining, dark bands are…

A

A-T rich, late replicating, heterochromatic

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28
Q

in g staining, light bands are…

A

C-G rich, early replicating, euchromatic.

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29
Q

why does C-banding let you see Roberts syndrome?

A

c banding stains constitutive heterochromatin. In Roberts syndrome the heterochromatin (centromeres) repels from each other in sister chromatids, causing premature separation

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30
Q

In ISCN, in what order do you list abnormal chromosomes?

A

sex, then autosomal, starting with lowest

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31
Q

In ISCN, where do you put “mat” or “pat”

A

right after change. Ex: 46,XX,inv(14)(q12q31)pat

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32
Q

ISCN ::

A

break and rejoining

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33
Q

ISCN “add”

A

additional material of unknown origin

34
Q

ISCN “r”

A

ring chromosome

35
Q

ISCN “i”

A

isochromosome

36
Q

ISCN “arr”

A

microarray

37
Q

46,XX.ish 22q11.2(D22S75x2)

A

Interpretation: Female with normal karyotype by cytogenetic analysis and is normal by ish using a probe for locus D22S75

38
Q

Interphase

A

G1, S, G2

39
Q

Mitosis phases

A

prophase, metaphase, anaphase, telophase

40
Q

2 sources of genetic variation in gametes

A

independent assortment, recombination

41
Q

at what stage are oocytes arrested prior to menstruation?

A

prophase 1

42
Q

what happens to oocyte during menstruation?

A

completes meiosis 1 and produces first polar body

43
Q

Aneuploidy vs euploidy

A

aneuploidy is a difference from the normal 46. Euploidy is a difference in the set number

44
Q

sources of aneuploidy

A

anaphase lag, nondisjunction, premature centromere division

45
Q

most common autosomal trisomy

A

trisomy 16- but not compatible with life

46
Q

Autosomal aneuploidies largely contributed by

A

mom

47
Q

Mosaicism

A

more than one cell line, but all derived from same original zygote

48
Q

Chimerism

A

distinct cell lines within an individual. Fusion of two conceptions. Usually confined to specific tissue(s)

49
Q

does mitotic nondisjunction carry risk for UPD?

A

no

50
Q

Recurrence of autosomal dominant disorders in multiple sibs born to normal parents may suggest

A

gonadal mosaicism

51
Q

Cornelia de Lange syndrome features

A

eyebrows that meet in the middle, long eyelashes, short upturned nose thin downturned lips

52
Q

ISCN rules for mosaicism

A

separated by slash. normal karyotype listed last. number of cells analyzed but in brackets

53
Q

Isodisomy

A

inheritance of two copies of the same homolog from one parent

54
Q

heterodisomy

A

inheritance of two different homologs from one parent

55
Q

Mechanisms for generating UPD

A

Trisomy rescue, Gamete complementation, Monosomy rescue/mitotic duplication, Somatic crossing over

56
Q

what % of viable pregnancies show confined placental mosaicism?

A

2%

57
Q

nips lower limit of fetal fraction

A

4%

58
Q

how long are fetal dna fragments in blood?

A

about 200 bases

59
Q

whole chromosome aneuploidy usually from

A

mom

60
Q

de novo balanced structural rearrangements usually from

A

dad? really?

61
Q

deletion syndrome examples

A

cri du chat, Wolf-Hirschhorn, williams, Alagille, DiGeorge

62
Q

duplication syndrome examples

A

beckwith-wiedemann, cat eye

63
Q

paracentric inversions

A

do not include centromere. both breaks on one arm. can lead to dicentric and acentric chromosome in meiosis during crossover

64
Q

pericentric inversions

A

include centromere. one break on each arm. generate chromosomes with one centromere in meiosis (normal)

65
Q

most common structural rearrangement

A

robertsonian (13;14 most common)

66
Q

telemere gene density

A

There is a very high density of genes at the telomeres, and recombination rates are higher at the telomeres than at other regions of the chromosomes. The end of each chromosome is capped with 3 - 20 kb of TTAGGG repeat.

67
Q

Number of cross overs per meiosis

A

2.4 per chromosome pair for males. Higher for females

68
Q

Nondisjunction

A

failure of chromosomes (during meiosis I) or chromatids (during mitosis or meiosis II) to separate at anaphase

69
Q

Anaphase lag

A

failure of a chromatid or chromosome to attach to the spindle and segregate into a daughter cell

70
Q

Parental origin of triploidy

A

85% paternal

71
Q

Among couples with two or more SABs, X% of the couples will have a chromosome abnormality (usually a translocation or inversion).

A

6% of the couples (3% of individuals in those couples)

72
Q

Placental mosaicism seen at CVS is associated with true fetal mosaicism ~X% of the time.

A

10% (still current?)

73
Q

Breakdown of Down syndrome cause

A

85-90% maternal meiosis (75% M1, 25% M2)
3-5% paternal meiosis (25% M1, 75% M2)
4% robertsonian translocations (75% de novo, 25% familial, though depends on which robertsonian)
3-5% mitotic

74
Q

Inversions: Small distal segments lead to ___ imbalances and___ (sometimes very large) risks.

A

Small distal segments lead to small imbalances and large risks.

75
Q

Inversions: Large distal segments lead to ___ imbalances and relatively ___ risks for having liveborn abnormal children and ___ risks for period of infertility or miscarriages.

A

Large distal segments lead to large imbalances and relatively low risks for having liveborn abnormal children and high risks for period of infertility or miscarriages.

76
Q

Partial ___ are usually more lethal than partial ___.

A

Partial monosomies are usually more lethal than partial trisomies.

77
Q

___ segregation of a quadrivalent pairing will yield normal and balanced gametes

A

Alternate

78
Q

Supernumerary marker chromsomes

A

Extra structurally abnormal chromsomes whose origin or makeup are not apparent by traditional cytogenetic analysis.

79
Q

Potential gametes of large, direct insertions

A

Normal, balanced, del, or dup.

If quadrivalent forms in meiosis, an odd number of crossovers occur, can get gametes with del and dup

80
Q

Potential gametes of pericentric inversions

A

Normal, balanced.
Uneven number of crossovers in meiosis can lead to gametes with del and dup
If distal segments are large, not likely to be viable

81
Q

Potential gametes of paracentric inversions

A

Normal, balanced.

Recombinant offspring pretty much impossible because chromosome would have incorrect number of centromeres

Cytogenetics (2 decks)

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