Cytogenetics - human chromosomes and disorders Flashcards

1
Q

what are microsatellites?

A

repeated units of DNA

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2
Q

what is an aneuploidy?

A

one or more individual chromosomes in extra copy or missing

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3
Q

how many chromosomes do humans have?

A

46 chromosomes

(23 from mom and 23 from dad)

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4
Q

in a normal karyotype picture, what do the dark bands represent? What do the light bands represent?

A

dark bands= heterochromatin (AT rich and gene poor region)

light band = euchromatin (GC rich and gene rich)

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5
Q

describe the banding nomenclature of chromosomes

ex) 1p13.3

A

1p13.3 refers to the

1st chromosome

p= short arm of chromosome

13= region of the chromosome

3= sub-band of region

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6
Q

what are the two basic types of chromosome abnormalities?

A
  1. numberical aberrations
    1. like trisomy (47 chromosomes) or monsomy (45 chromosomes)
  2. structural aberrations
    1. involving 1 chromosome- deletion , duplications, inversion, ring chromosome
    2. involving 2 chromosomes - translocations
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7
Q

how does aneuploidy arise?

A

from chromosomal non-disjunction

  • failure of homologous chromosomes to separate and segregate normally in either mitosis or meiosis
  • when it occurs in meiosis, non-disjunction results in imbalances gametes - should one of those gametes fertilize, all cells derived from the resulting embryo will have a chromosome imbalance
  • when it occurs in mitosis - nondisjunction produces two cell-lineages derived from a single zygote (known as mosaicism)= less severe syndrome
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8
Q

when does non-disjunction occur in meiosis?

A

non-disjunction can occur in either the first or second meiotic division and consequences are different

first = gametes contain either both parental chromosomes which failed to separate or neither

second = gametes contian two identical copies of the same chromosome or neither

zygotes will either bet monosomic or trisomic

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9
Q

what are some clinical features of down syndrome?

A
  • developmental delay
  • variable intellectual disability
  • characteristic facial features
  • congenital heart defects
  • premature ageing
  • risk of leukaemia
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10
Q

what is the incidence of trisomy 21?

A

1/650 live-births (about 50% spontaneous abortions)

risk increases with maternal age

30 yr= 1/900

36 year= 1/300

40 yr= 1/100

44 yr = 1/40

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11
Q

What is trisomy 18?

A

Ewards Syndrome= rocker-bottom feet, usually die within 1 year

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12
Q

What is Trisomy 13?

A

Patau syndrome = polydactyly, death usually within 1 year

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13
Q

what is monosomy X?

A

Turner syndrome

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14
Q

what is kleinefelter syndrome?

A

extra x chromosome male

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15
Q

what is a reciprocal translocation of chromosome?

A

where two chromosomes swap genetic material

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16
Q

what is a robersonian translocation?

A

where part two chromosomes combine

17
Q

what test is used to detect microdeletion syndromes?

A

fluorescence in situ hybridization = FISH

  • also used to detect estrogen dependent cancer -
18
Q
A
19
Q

what does ‘imprinting’ mean in genetics ?

A

different expression of the same chromosomal region depending on whether the region was inhertied from mom or dad

*DNA methylation differences responsible for altered gene expression*

20
Q

what is an Array CGH used for?

A

it is the ‘gold standard ‘ for future genetic testing

detects highly subtle gain or loss of genetic material - significantly more sensitive than G-band karyotyping

-same resolution as FISH but is genome-wide detection method

21
Q

when do we use G-band karyotyping, FISH or Array CGH?

A

large chromosome syndromes = g band karyotyping or FISH

translocations = g band karyotyping

microdeletions = FISH

unexplained developmental delay or congenital malformations = Array CGH