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302 genetics > anneuploidy- genetics 1 > Flashcards

anneuploidy- genetics 1 Flashcards

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Biology 101 flashcards
1
Q

what is the function of a chromosome?

A

vessels of genetic inheritance

Allow DNA to be stably maintained Package 2.17m long DNA into 40μm nucleus

Allows DNA to be replicated and segregated

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2
Q

how many genes do humans have?

A

3.2 billion bp, ~20.000 genes

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3
Q

label the following

A
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4
Q

what are the 3 different types of chromosomal structures?

A

Metacentric - centromere placed in middle
Sub-metacentric - closer to one telomere
Acrocentric - centromere near telomere

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5
Q

describe the human karyotype

A

2 haploid sets of 23 chromosomes
44 autosomes, 2 sex chromosomes

arranged according to G banding and size

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6
Q

what are the 2 main types of chromosomal abnormalities?

A

Aneuploidy – too many or too few chromosomes
Structural – chromosome rearrangements

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7
Q

what is the most common cause of anneuploidy?

A

maternal non dysjunctin in meiosis 1

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8
Q

what are thedifferent combinations of abnormal gametes that can arrise?

A
  1. trisomic conceptus
  2. monosomic conceptus
  3. uniparental disomy
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9
Q

what is mosacism?

A

Mosaicism is when a person has 2 or more genetically different sets of cells in his or her body- some cells may have 46 chromosomes and some may have either more orless-

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10
Q

describe the daughter cells if nondysjunction occurs in meiosis 1

A
  • 2 gametes with an extra chromosome
  • 2 gamaetes with a chromosome missing
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11
Q
A
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12
Q

describe the daughter cells if non dysjunction occurs in meiosis 2

A

1 daughter cell with an extra chromosome

1 daughter cell with missing chromosome

2 daughter cells with normal chromosomes

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13
Q

what are the 2 different ways that mosaicism can occur that will result in conditions like downsyndrome?

A
  1. post zygotic non- dysjunction
    - this is when a normal coceptus zygote will undergo non dysjunction during mitosis and this will lead to some cells having 47 chromosomes and others having 45- the cells with 45 chromosomes are less likely to survive, but the cells with 4 7 chromosomes will go on to proliferate- if nondyjunction occurs earlier on more cells will have trisomy, but if it occurs later on less cells will hav trisomy
  2. Anaphase lag
    - this is when the zygote starts with trisomy 21, the sister chromatids do not seperate properly from eachother resulting in soem cells with 48 chromosomes and some cells with 46

the cells with 48 chromosomes die off, but the cells with 46 chromosomes continue to proliferate. this increases the number of cells with a normal chromosome number

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14
Q

what is the downsyndrome phemotype?

A

learning difficulties,
dysmorphic features,
heart defects
Alzheimer’s 20-30 years earlier

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15
Q
A
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16
Q

which chromosome is affected in downssyndrome?

A

trisomy 21

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17
Q

what are the 3 different types of karyotypes that can occur in don syndrome?

A
  1. 95% primary (full) trisomy : 47,XX,+21 (or 47,XY,+21)
  2. 1-2% mosaicism: 46,XX/47,XX,+21 (or XY)
  3. 4% translocation: 46, XX,der(14;21)(q10),+21 (or XY)
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18
Q

what is the name given to those with trisomyy 21

A

edwards syndrome

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19
Q

what is the phenotype for edwards syndromes?

A
  • SEVERE MENTAL DISABILITY
  • DYSMORPHIC FEATURES: MICROGNATHIA, PROMINENT OCCIPUT
  • ROCKER-BOTTOM FEET,
  • CLENCHED FISTS WITH OVERLAPPING FINGERS
  • CONGENITAL HEART DEFECTS
    MANY DIE WITHIN WEEKS, 90% WITHIN 1 YEAR
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20
Q

which type of translocation can cause downsyndrome?

A

robertsonian

21
Q

what is trisomy 13?

A

patau’s syndrome

22
Q

what is the phenotype for pataues syndrome?

A
  • SEVERE MENTAL DISABILITY
  • DYSMORPHIC FEATURES (CLEFT LIP AND PALATE, POLYDACTYLY, HOLOPROSENCEPHALY)
  • RENAL ABNORMALITIES,
  • CARDIAC DEFECTS

MANY DIE WITHIN WEEKS, 95% WITHIN 1 YEAR

23
Q

Q17. what is the mechanism of 20% of patau’s syndromes?

A

translocation

24
Q

what are the 3 types of sex chromosome trisomies?

A
  1. Klinefelter syndrome (XXY)
  2. XYY syndrome
  3. Triple X syndrome (XXX)
25
Q

what is the chromosomal cause of turners syndrome?

A

x chromosome monosomy

26
Q

what is the phenotype for turner syndrome?

A
27
Q

in which aneuploidy is maternal age not a risk factor?

A

turners syndrome

28
Q

what is the phenotype for klienfelter syndrome?

A
  • tall stature, long limbs
  • gynaecomastia (30-50%)
  • small testes, sometimes Crypthochirdism
  • infertility, azoospermia
  • Delayed or incomplete puberty
29
Q

what is the phenotype for XXX syndrome?

A
  • largely asymptomatic
  • in 10% seizures or kidney abnormalities
  • may be taller but usually does not cause unusual physical features,
  • no infertility
  • increased risk of learning disabilities and delayed development of speech and language skills
30
Q

what is the phenotype for XYY?

A
  • often asymptomatic
  • symptoms may include;
  • learning disabilities,
  • speech delay,
  • low muscle tone (hypotonia),
  • being taller than expected
    usually normal sexual development, and normal fertility, sometimes develop testicular failure
31
Q

why do autosomal aneuploidys cause a more severe phenotype than sex chromosome anneuploidy?

A
  • Due to x chromosome inactivation – lyonisation
  • 2 weeks post-fertilisation
    in descendent cells, the same X remain active/inactive
    XXY, XXX, XXXX: always one X remains active
32
Q

what is the mechanism for chromosome ring formation?

A
  • TELOMERES ARE LOST LEAVING STICKY ENDS
  • THESE ENDS JOIN TOGETHER AND FUSE
33
Q

what is the mechanism for X inactivation ?

A

X-inactive specific transcript RNA (Xist) expressed on inactive X

Xist transcripts coat X chromosome
leading to inactivation

34
Q

what are the different types of structural abnormalities that can occur in chromosomes?

A

Translocation,

inversion,

deletion,

duplication,

all of these can either be balanced or non balanced
Balance (no loss of genetic material) vs unbalanced (exchange of chromosome material as in deletion and duplications)

35
Q

what is translocation?

A

A translocation occurs when a piece of one chromosome breaks off and attaches to another non homologous chromosome
or on a new site on the same chromosome

36
Q

is isochromosome formation balanced or unbalanced? how does it occur?

A

CENTROMERE FISSION

  • TWO IDENTICAL ARMS
  • EITHER 2 P ARMS OR 2 Q ARMS JOIN TOGETHER
  • ONE DUPLICATED, OTHER DELETED
  • SO FORMATION OF ISOCHROMOSOME IS ALWAYS UNBALANCED AS THE GENES ON EITHER LONG OR SHORT ARM ARE ALWAYS LOST
37
Q

What is the mechanism of duplication and deletions?

A

Misalignment of homologous chromosomes during meiosis results in allelic product that a reciprocally imbalanced

This will result in one allele having a duplication of a gene and another having a deletion of the same gene

38
Q

Which syndromes are associated with deletion and duplication of genes on chromosome 17 respectively?

A

Deletion= smith magenis syndrome

duplication= potoki lupski syndrome

39
Q

decribe what occurs in robertonian translocaton

A
40
Q

compare and contrast reciprical translocation with robersontian translocation

A
41
Q

in which type of translocation is a trivalent formed instead of a bivalent during translocation?

A

robertsonian

A TRIVALENT IS FRMED INSTEAD OF A BIVALENT

  • THIS CAN SPLIT IN 3 DIFFERENT WAYS
  • TO PRODUCE 6 DIFFERENT GAMETES
  • half will result in inviable miscariage
  • 2/3 will be either normal or carrier
  • 1/3 of live births will be downsyndrome
42
Q

what is a chromosomal translocation

A

the exchange of genetic materrials between non homologous chromosomes

43
Q

why can reciprial translocated indviduals have problems in their gametes?

A
  • during meiosis the translocated chromosomes will have homology with more than one other chromosome
  • quadravalents will form intead of bivalents
  • this will make segreation more complicated
  • there will be 5 possible pairs of daughter gametocytes
44
Q

what can cause cru du chat syndrome?

A

deletions in the p orm of chromosome 5

symptoms are dependent on the length of the deletion

45
Q
A
46
Q

how can cri du chat result from a translocated parent?

A

e.g. father has balanced translocation of chromosomes 5 and 11

passes translocated chromosome 5 to child but child inherits normal chromosome 11 from mother

the child will have an unbalanced translocation as the material lost on the fathers chromosome 5 is not made up by any other chromosome

this will result in cri du chat

47
Q

what s the main mechanism by which cri du chat mutation occurs?

A
  • denovo mutation
48
Q
A

302 genetics (4 decks)

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