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EMS > Lecture 11: Chromosomal pathology > Flashcards

Lecture 11: Chromosomal pathology Flashcards

1
Q

Give the 4 broad chromosomes changes that produce an abnormal change:

A

1) dosage effect

2) disruption of a gene at a break point

3) position effect

4) unmasking of a recessive disorder

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2
Q

How may a chromosomal change lead to the unmasking of a recessive disorder?

A

if a dominant chromosome in a heterozygous pair is deleted, a recessive phenotype may present

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3
Q

Give the three types of copy number variation:

A

1) chromosome number

2) chromosome structure

3) mosaicism

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4
Q

What does aneuploidy mean?

A

Abnormal number of chromosomes

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5
Q

What does euploidy mean?

A

normal number of chromosomes

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6
Q

What does polyploidy mean?

A

condition in which an organism has extra sets of chromosomes

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7
Q

What is chromosome mosaicism?

A

different cells containing different chromosomal makeup

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8
Q

What is the most common cause of aneuploidy?

A

meiotic non-disjunction

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9
Q

What is non-dysjunction?

A

failure of chromosome or chromatid separation

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10
Q

True or false: in aneuploidy, maternal age has a large effect whereas paternal age has little to no effect

A

true

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11
Q

Describe how non-disjunction in meiosis can cause aneuploidy:

A

non-disjunction can lead to disomic gamete which will then fuse with a normal monosomic gamete at fertilisation to form a trisomic zygote

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12
Q

What is the name of trisomy 21?

A

Down syndrome

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13
Q

What is the name of trisomy 13?

A

Patau syndrome

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14
Q

What is the name of trisomy 18?

A

Edwards syndrome

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15
Q

Give 5 characteristics of Down syndrome:

A

1) learning difficulties

2) heart malformations

3) gut atresia

4) early dementia

5) leukaemia

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16
Q

Give 4 characteristics of Patau syndrome;

A

1) microcephaly

2) holoprosencephaly

3) clefting

4) polydactyl

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17
Q

What is holoprosencephaly?

A

failure of left and right hemispheres to separate

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18
Q

What is holoprosencephaly?

A

failure of left and right hemispheres to separate

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19
Q

Give 5 characteristics of Edwards Syndrome:

A

1) microcephaly

2) growth retardation

3) rocker-bottom feet

4) clenched hands

5) cardiac anomalies

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20
Q

Why is it that only trisomies 21, 18 and 13 are viable?

A

because chromosomes 21, 18 and 13 are small and have few genes meaning life can still be sustained (larger chromosomes are required for life)

21
Q

True or false: sex chromosome aneuploidy tends to be more severe than autosomal aneuploidy

A

False

22
Q

What is the name of the sex chromosome aneuploidy with just one X chromosome?

A

of the sex chromosome aneuploidy with just one X chromosome?
Turner syndrome (45 X)

23
Q

Give 4 characteristics of Tuner syndrome (45 X):

A

1) short stature

2) infertile

3) neck webbing

4) aortic coarctation

24
Q

What is the name of the sex chromosome aneuploidy where there are two X chromosomes and one Y chromosome?

A

Klinefelter syndrome (47 XXY)

25
Q

True or false: 99% of polyploidy cases result in spontaneous miscarriage

A

True

26
Q

How does polyploidy come about?

A

either an eggy is digyny or there are two sperm (dispermy) at fertilisation

27
Q

Give two types of cytogenetic chromosome analysis methods:

A

1) karyotyping

2) FISH

28
Q

What is FISH (fluorescent in situ hybridization)?

A

using fluorescent DNA probes to identify specific genes or a lack of

29
Q

What is the name of the disease caused by a microdeletion at 22q11.2?

A

DiGeorge Syndrome

30
Q

Give four DNA based chromosome analysis methods:

A

1) chromosomal microarrays

2) whole genome sequencing

3) multiple ligation dependent probe amplification

4) quantitative fluorescent PCR

31
Q

Give three benefits of using chromosomal microarrays over karyotyping:

A

1) higher resolution

2) greater diagnostic rate

3) only needs DNA, rather than live cells

32
Q

What type of chromosome change can karyotyping identify that microarrays can’t?

A

balanced rearrangements

33
Q

What is copy number variation?

A

A difference in the amount of a specific DNA sequence found in different individuals

34
Q

What is copy number variations sequencing?

A

a method that looks to identify variations in copy numbers by sequencing DNA, cutting it into fragments then using computer alignment to count copy numbers

35
Q

What is a reciprocal translocation?

A

where regions of chromosomes break off and exchange with another chromosome

36
Q

What arrangement is formed by translocated chromosomes when matching up for meiosis?

A

meiotic quadrivalent/ pachytene cross

37
Q

Does adjacent segregation of a pachytene cross result in balanced or unbalanced segregation?

A

Unbalanced

38
Q

Does alternate segregation of a pachytene cross result in balanced or unbalanced segregation?

A

Balanced

39
Q

What is a Robertsonian translocation?

A

The long arms of two acrocentric chromosomes are joined to a common centromere through translocation, resulting in a large metacentric chromosome and a very small chromosome with two very short arms

40
Q

What are acrocentric chromosomes?

A

chromosomes which have small short arms

41
Q

Give the 5 acrocentric chromosomes:

A

13, 14 15, 21 and 22

42
Q

When is quantitative fluorescent PCR used?

A

Urgent situations

43
Q

Describe how quantitative fluorescent PCR works:

A

a DNA sample is targeted for important aneuploidies using markers for abnormal dosage and paternal and maternal material is compared by capillary electrophoresis

44
Q

What two methods can result in mosaicism?

A

1) mitotic non-disjunction

2) trisomy rescue

45
Q

What is trisomy rescue?

A

genetic phenomenon in which a fertilized ovum containing three copies of a chromosome loses one of these chromosomes to form a normal, diploid chromosome complement

46
Q

What are isochromosomes?

A

a chromosome made out of two long or short arms

47
Q

What genetic disorder is caused by mosaic tetrasomy of the 12p isochromome?

A

Pallister-Killian syndrome

48
Q

Give two characteristics of Pallister-Killian syndrome:

A

1) intellectual deficit

2) seizures

EMS (54 decks)

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