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BIO 350 - Medical Genetics > Lecture 5 - Clinical Cytogenetics > Flashcards

Lecture 5 - Clinical Cytogenetics Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

What is cytogenetics?

A

It is the study of chromosomes and their abnormalities

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2
Q

What is a karyotype?

A

The number and type of chromosomes present in an individual

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3
Q

What is the actual printed display of chromosomes called?

A

A karyogram

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4
Q

How are chromosomes classified?

A

According to size, then shape

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5
Q

What different kinds of shapes are their for chromosomes?

A

Metacentric (centromere in middle); Acrocentric (centromere near tip); and Submetacentric (between middle and tip)

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6
Q

What would the karyotype designation of a normal female be?

A

46,XX

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7
Q

What is the karyotype of a male with Down’s syndrome?

A

47,XY + 21

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8
Q

What is the karyotype of Turner’s Syndrome?

A

45,X

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9
Q

What can be done to the chromosomes in a lab setting for a karyogram?

A

There are many different stains and techniques to visualize chromosomes

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10
Q

What is FISH?

A

A technique in which a labelled probe (ssDNA) is hybridized to metaphase, prophase, or interphase chromosomes

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11
Q

What can FISH be used for and how?

A

To test for missing or additional chromosomal material as well as chromosome rearrangements. In a normal person, the probe will bind in 2 places. If it is in only 1 spot, then the patient probably has a deletion in the other chromosome.

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12
Q

What is spectral karyotyping?

A

A special form of the FISH technique to simultaneously visualize all the chromosomes in various colors

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13
Q

What is CGH and what is it used for?

A

Comparative genomic hybridization (CGH) can be used to detect deletions or duplications of whole chromosomes or regions

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14
Q

What are the differences between CGH versus Array CGH?

A

Array CGH can locate abnormalities at a higher resolution, while CGH can’t see deletions/duplications <5-10Mb

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15
Q

What is a disadvantage of FISH?

A

You have to know what you are looking for

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16
Q

What is euploid?

A

A cell that contains a multiple of 23 chromosomes

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17
Q

What is polyploidy?

A

The presence of a complete set of extra chromosomes

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18
Q

What are some examples of polyploidy in humans? Give the karyotypes for your examples.

A

Triploidy (69,XXX) ; Tetraploidy (92,XXXX)

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19
Q

What is the most common cause of triploidy?

A

The fertilization of an egg by two sperm (dispermy)

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20
Q

What are some other causes of triploidy?

A

The fusion of an ovum with a polar body, then fertilization by a sped. Also, meiotic failure which results in a diploid egg or sperm being produced.

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21
Q

How can you get a tetraploid baby?

A

Mitotic failure in the early embryo where all of the duplicated chromosomes migrate to one of the two daughter cells.

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22
Q

What is aneuploidy?

A

Cells with missing or additional individual chromosomes (not multiple of 23)

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23
Q

What kind of chromosome disorder is Turner’s Syndrome?

A

Monosomy

24
Q

What is the survival rate of trisomies compared to monosomies? Why?

A

Trisomies are seen at a higher frequency in the population because the body can tolerate an excess of DNA easier. Most monosomies are incompatible with survival to term, which is why they are less frequent.

25
Q

What is the most common cause of aneuploidy?

A

Nondisjunction

26
Q

What is nondisjunction?

A

The failure of chromosomes to separate normally in meiosis

27
Q

Why are older women more likely to have children with Down’s Syndrome?

A

Because their ova are the same age as them, which increases the chances of nondisjunction occurring. The oocytes remain suspended in Prophase 1 for their entire lives

28
Q

What is the gene required to be a male?

A

The SRY gene, which is found on the Y chromosome

29
Q

What does the protein from SRY do?

A

It is a transcription factor that bends the DNA

30
Q

How is it possible to have an XX male?

A

During meiosis in the father, faulty crossing over happened between the X and Y chromosome, where the SRY gene got transferred to the X chromosome, which ended up going to the offspring

31
Q

What is an unbalanced chromosome rearrangement?

A

A chromosomal rearrangement that results in gain or loss of chromosomal material

32
Q

What are the different types of translocation?

A

Robertsonian and reciprocal

33
Q

What is a reciprocal translocation?

A

When breaks occur in two different chromosomes and the material is mutually exchanged. The resulting chromosomes are called derivative chromosomes.

34
Q

How is the status of someone who carries a reciprocal translocation?

A

They are usually fine, as they have all of the DNA they need. However, their offspring can either be normal, carry the translocation, or have duplications/deletions

35
Q

What is a Robertsonian translocation?

A

It is when the short arms of two non-homologous chromosomes are lost and the long arms fuse.

36
Q

What is the status of someone with a Robertsonian translocation?

A

They are usually normal, since they didn’t lose essential genetic material. However, they have 45 chromosomes in each cell. Their offspring can be normal, have the same translocation, or have a trisomy/monosomy

37
Q

What are the 2 different types of deletions?

A

Terminal deletion (loss of tip); Interstitial deletion (internal bit)

38
Q

What are microdeletion syndromes? What can be used for them?

A

Syndromes where the chromosomal defect cannot be seen through a microscope
The FISH technique and the development of a large # of polymorphisms

39
Q

What is an example of a micro deletion syndrome?

A

Prader-Willi Syndrome

40
Q

What is a contiguous gene syndrome?

A

Syndromes caused by the deletion of a series of adjacent genes

41
Q

What are subtelomeric rearrangements and what do they usually account for?

A

Subtelomeric rearrangements involve deletions/duplications in gene rich regions near the telomeres
They usually lead to mental retardation

42
Q

What are the two main causes of Prader-Willi Syndrome?

A

Uniparental disomy and microdeletions

43
Q

What is uniparental disomy?

A

A condition where only one parent has contributed the two copies of a chromosome

44
Q

What is the difference between isodisomy and heterodisomy? What do they have to do with?

A

They are both forms of uniparental disomy.
If the parent gave 2 copies of one homolog, it is isodisomy.
If the parent gave 1 copy of each homolog, it is heterodisomy.

45
Q

How is uniparental disomy related to PW syndrome?

A

See pg. 122

46
Q

How do duplications come about? How are they compared to deletions?

A

Duplications or partial trisomy can arise from unequal crossover, or they can occur among the offspring of reciprocal translocation.
Duplications compared to deletions of the same region are generally not as bad.

47
Q

What is an inversion?

A

It is the result of two breaks on a chromosome, followed by reinsertion of the fragment at the original site except backwards

48
Q

What are the different types of inversions?

A

Pericentric inversions include the centromere; paracentric inversions don’t

49
Q

Do inversions typically result in a disease?

A

No, because no loss of genetic material

50
Q

Which kind of inversion is special?

A

Pericentric, because it can interfere with meiosis in carriers. A loop forms, in which duplications or deletions can be produced in the resulting gamete, affecting the offspring

51
Q

What is an isochromosome?

A

A chromosome that has 2 copies of one arm, but none of the other

52
Q

How are isochromosomes generated?

A

Faulty separation of the chromosomes, where the axis of division is perpendicular to normal.
Also, a Robertsonian translocation of homologous acrocentric chromosomes

53
Q

Which isochromosome formed is usually observed in live births?

A

The X chromosome, leading to features of Turner’s syndrome

54
Q

What kind of phenotypes are expected in general with chromosome abnormalities?

A

Developmental delay, mental retardation, facial characteristics, and various types of congenital malformations

55
Q

What kind of mutations could cause cancer?

A

Point mutations, Gene amplification, Chromosomal translocations, Local DNA rearrangements, and Insertional mutagenesis

56
Q

What are some examples of oncogenes?

A

Growth factors and receptors, G-proteins (eg. RAS), Protein kinases, Transcription factors, CDK-cyclins

57
Q

What are chromosomal instability syndromes?

A

Autosomal recessive conditions that exhibit an increased frequency of chromosome breaks under certain conditions

BIO 350 - Medical Genetics (10 decks)

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