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MCG Review > RL Lectures 41 and 42: Chromosomes and Cytogenetics > Flashcards

RL Lectures 41 and 42: Chromosomes and Cytogenetics Flashcards

1
Q

What causes the majority of spontaneous abortions in the first trimester?

A

chromosomal abnormalities

66%

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2
Q

What is the overall incidence of chromosomal abnormalities in the live born population?

A

~1 in 125

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3
Q

When are chromosomes visible?

A

mitotic phase of the cell cycle

karyotype requires cells that are spontaneously dividing or in cells where division has been induced

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4
Q

How is karyotyping performed?

A

blood sample is taken and G-banding procedure allows for discrimination of banding per chromosome which can identify all 23 pairs of chromosomes

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5
Q

List the sections of the chromosomes.

A

p-arm (short arm)
q-arm (long arm)
centromere (central condensed region essential for mitotic spindle attachment)
telomere (cap at the end)

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6
Q

What are metacentric chromosomes?

A

chromosomes whose arms have very similar lengths

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7
Q

What are sub-metacentric chromosomes?

A

chromosomes where the p-arm is visually shorter than the q-arm

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8
Q

What are acrocentric chromosomes?

A

chromosomes where the p-arm is very short and only contains repetitive information and ribosomal RNA genes

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9
Q

List the acrocentric chromosomes.

A

13, 14, 15, 21, and 22

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10
Q

List the kinds of aneuploidy.

A

monosomy/ deletion (missing chromosome or missing part of a chromosome)
disomy/ duplication (additional chromosome or part of a chromosome)

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11
Q

How do aneuploidys occur?

A

failure of the chromosomes to properly segregate during division (most commonly meiotic 1 non-dysjunction)

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12
Q

What is Down Syndrome?

A 
Trisomy 21
most common trisomy seen in live births
1 in 800
95% due to meitotic 1 non-dysjunction
highly correlated with AMA
life expectancy ~60 years
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13
Q

What are the symptoms associated with Down Syndrome?

A 
ID
short stature
hearing loss
seizures
heart malformations
digestive tract malformations
increased disease risk
distinct facial features
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14
Q

What is Edward Syndrome?

A

Trisomy 18
1:6,000 live births
95% result in spontaneous abortion or miscarraige
poor survival rates (4 days average)

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15
Q

List the symptoms of Edward Syndrome.

A 
rocker bottom feet
overlapping fingers
multiple congenital organ anomalies
restricted growth
microcephaly
short palpebral fissures
small chin and mouth
low-set ears
cutis aplasia
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16
Q

What is Patau Syndrome?

A

Trisomy 13
1 in 10,000 live births
life expectancy about 130 days

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17
Q

What features are present in babies with Patau Syndrome?

A 
distinctive midline defects (cleft lip/palate)
multiple congenital organ anomalies
hypertelorism
holoprosencephaly
polydactyly
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18
Q

Describe trisomy mosaicism.

A

typically have attenuated features of the trisomy

result from non-dysjunction of the chromosomes after fertilization

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19
Q

What is Turner Syndrome?

A

Monosomy X
1 in 5,000 live female births
99% of embryos spontaneously aborted
loss of PAR region

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20
Q

What are the symptoms associated with Turner Syndrome?

A 
webbed neck
lymphedema
short stature
coarctation of aorta
structural kidney defects
ovarian dysgenesis
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21
Q

What is PAR?

A

pseudoautosomal regions

repeat sequences at both ends of sex chromosomes that act as autosomal genes and escape X-inactivation

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22
Q

What is Kleinfelter syndrome?

A

47,XXY
1 in 1000 live male births
half maternal and half paternal in origin
one X chromosome is inactivated but three pairs of PAR regions are still expressed

23
Q

What symptoms are associated with Kleinfelter Syndrome?

A 
small testes
low testosterone
geynecomastia
no spermatogenesis
taller and thinner
learning issues
ADHD
24
Q

What is Super Female Syndrome?

A

47, XXX
1 in 1000 female births
mostly maternal in origin
only one X is active but still have three pairs of PAR genes active

25
Q

List the symptoms of Super Female Syndrome?

A

tall stature
balance problems
generally fertile
risk of speech delay and learning issues

26
Q

What is Jacob syndrome?

A

47, XYY
1 in 1000 live male births
paternal in origin
only one X is active but three pairs of PAR regions are present

27
Q

What are the symptoms of Jacob Syndrome?

A

tall but normally proportioned

mostly completely asymptomatic

28
Q

What screenings can be used to detect risk of an aneuploidy in the first trimester?

A

NT
PAPP-A
f-bhCG

29
Q

What percent of pregnancies are lost due to aneuploidy per trimester?

A

1st: 66%
2nd: 20%

30
Q

What results on a first trimester screening would indicate increased risk for Down Syndrome?

A

increased NT
low PAPP-A
high f-bhCG

31
Q

What results on first trimester screening would indicate increased risk for Edward Syndrome?

A

increased NT
low PAPP-A
low f-bhCG

32
Q

What results on first trimester screening would indicate increased risk for Patau Syndrome?

A

increased NT
low PAPP-A
low f-bhCG

33
Q

What serum analyte screenings can be used to detect risk of aneuploidy in the second trimester?

A

estriol
inhibin A
hCG
AFP

34
Q

What results on a quad screening would indicate increased risk for Down Syndrome?

A

low AFP
low estriol
high hCG
high Inhibin A

35
Q

What results on a quad screening would indicate increased risk for Turner Syndrome?

A

decreased AFP
decreased estriol
very high hCG
very high inhibin A

36
Q

What results on a quad screening would indicate increased risk for Edward Syndrome?

A

low estriol
very low hCG
low AFP

37
Q

What results on a quad screening would indicate an increased risk for Patau Syndrome?

A

increased AFP

38
Q

How would you confirm the results of a triple or quad screening?

A

CVS

amnio

39
Q

What is uniparental diploidy?

A

normal number of chromosomes, but they are all from one parent
pathogenic (most clinically significant with chromosomes containing imprinted regions)

40
Q

What chromosomes contain imprinted regions?

A

6, 7, 11, 14, 15, 16

41
Q

What is the result of paternal origin uniparental diploidy?

A

complete hydatidiform mole (no fetal tissue, only trophoblast hyperplasia, leading to carcinoma)
results from an egg that lacks a nucleus and is fertilized by one normal sperm

42
Q

What is the result of maternal origin uniparental diploidy?

A 
ovarian teratoma (disorganized empbryonic material)
results from an activated unovulated oocyte
43
Q

What is triploidy?

A

having three sets of chromosomes (total of 69)

caused by polyspermy (fertilization of a normal egg with two sperm resulting in a partial mole containing fetal tissue)

44
Q

What is tetraploidy?

A

having four sets of chromosomes (total 92)

caused by failure of the first zygotic division (usually does not contain fetal tissue and is spontaneously aborted)

45
Q

Provide examples of deletion syndromes that can be visualized on karyotyping.

A

Wolf-Hirshhorn syndrome (4p16 terminal deletion)

46
Q

What are translocations and inversions?

A

abnormalities in which genetic material is not gained or lost, but rather relocated

47
Q

What is a balanced translocation?

A

a translocation where no genes are disrupted
occurs when there is a reciporcal interchange of genetic material between two non-homologous chromosomes
carriers typically have no phenotype but risk recurrent miscarraige or phenotypically abnormal offspring because gametes may be unbalanced

48
Q

What is a Robertsonian translocation?

A

exchange of a full q arm from one acrocentric (homologous or non-homologous) chromosome with the p-arm of another acrocentric chromosome resulting in the loss of the p-arm
all genetic material is still accounted for because p-arm is repetitive

49
Q

What is a pericentric inversion?

A

two breaks in one chromosome where the area inbetween the breaks inverts and rejoins including the centromere

50
Q

What is paracentric inversion?

A

two breaks in one chromosome where the area inbetween the breaks inverts and rejoins confined to only one arm (does not include centromeric region)

51
Q

What happens when homologous recombination occurs with an inversion?

A

an elaborate looped pairing is needed during meiosis

52
Q

What does the loop pairing during meiosis cause?

A

unbalanced chromosomal abnormality in the conceptus with a partial duplication of one end of the inverted region in conjugation with a partial deletion of the other end of the inverted region

53
Q

Describe the formation and results of ring chromosomes.

A

tip of p arm is fused with the q arm on the same chromosome
genetic material at the tip can be lost, creating a terminal deletion
easily loose the whole chromosome during mitosis

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