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LQB490 > Numerical and structural abnormalities > Flashcards

Numerical and structural abnormalities Flashcards

1
Q

What is aneuploidy?

A

A condition in which a person has one or more chromosomes above or below the normal chromosome number.

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2
Q

What gives rise to aneuploidy?

A

Non-disjunction

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3
Q

What is non-disjunction?

A

The failure of chromosome pairs to separate properly during cell division.

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4
Q

Non-disjunction gives rise to what two types of cell lines?

A

Monosomy and trisomy cell lines.

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5
Q

What usually happens to the monosomy cell line that results from non-disjunction?

A

It is likely to be severely disadvantaged and most likely will die out.

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6
Q

Non-disjunction at mitosis can result in what outcome (if viable)?

A

Mosaicism

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7
Q

What is mosaicism?

A

An individual in which some cells are normal and some are abnormal.

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8
Q

Non-disjunctions are more common in what kind of cell division?

A

Meiosis

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9
Q

Approximately how many conceptions are monosomic or trisomic?

A

25%

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10
Q

What is the term for the way in which chromosomes are distributed in meiosis?

A

Segregation

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11
Q

Scenario: all four gametes produce a child.

What would be the ratio of normal, trisome, and monosomy if non-disjunction occurred during meiosis I?

A

No normal, two trisomy, two monosomy.

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12
Q

Scenario: all four gametes produce a child.

What would be the ratio of normal, trisome, and monosomy if non-disjunction occurred during meiosis II?

A

Two normal, one trisomy, one monosomy.

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13
Q

What is the ISCN denotation for a translocation?

A

t

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14
Q

What is a translocation?

A

A two-way exchange of material between two chromosomes.

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15
Q

What is the most common type of translocation?

A

Balanced reciprocal translocation

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16
Q

What is meant by ‘balanced’ in a balanced reciprocal translocation?

A

Balanced means that no total genetic material was lost or gained in the translocation.

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17
Q

What is meant by ‘reciprocal’ in a balanced reciprocal translocation?

A

Reciprocal means that the genetic material from the two chromosomes was exchanged with each other.

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18
Q

Does a balanced reciprocal translocation always occur between the same arms of the chromosomes?

A

No (not necessarily)

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19
Q

How common are translocations in the normal population?

A

1 in 600

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20
Q

How does a reciprocal translation occur?

A

Breaks occur in one arm of each chromosome and the portions of chromosome material distal to the breakpoints switch positions.

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21
Q

Breaks occurring in one arm of each chromosome and the portions of chromosome material distal to the breakpoints switching positions is a description of what type of structural abnormality?

A

Translocation

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22
Q

What is the term for the portions exchanged between chromosomes in reciprocal translocation?

A

Translocated segments

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23
Q

What is the term for the remainder of the chromosome (the portions NOT exchanged) including the centromere in reciprocal translocation?

A

Centric segment

24
Q

What is a centric segment?

A

The remainder of chromosomes including the centromere (i.e. the portions NOT exchanged) in reciprocal translocation.

25
Q

What is the term used for the rearranged chromosome following translocation?

A

Derivative chromosome (der).

26
Q

What is the ISCN denotation for a derivative chromosome?

A

der

27
Q

What is a derivative chromosome?

A

A rearranged chromosome following translocation.

28
Q

How are derivative chromosomes identified?

A

By which centromere it possesses.

29
Q

What type of chromosome is identified by which centromere it possesses?

A

Derivative chromosome

30
Q

What would be the denotation for a chr 5 with part of a translocated p arm from chr 10?

A

der(5)

31
Q

What would be the denotation for a chr 10 with part of a translocated q arm from chr 5?

A

der(10)

32
Q

Do balanced translocation carriers display phenotypical abnormalities?

A

No

33
Q

Do unbalanced translocation carriers display phenotypical abnormalities?

A

Yes

34
Q

What type of issues do balanced translocation carriers often have?

A

Fertility issues, often involving multiple consecutive miscarriages.

35
Q

Is it possible for a balanced translocation carrier to produce a genetically and phenotypically normal offspring?

A

Yes

36
Q

Scenario: all four gametes produce a child.

What would be the ratio of normal : balanced translocation carrier : unbalanced translocation carrier in the offpring of a balanced translocation carrier and a normal genotype?

A

1 normal : 1 balanced translocation carrier : 2 unbalanced translocation carriers.

Note: these are abnormalities and in reality do not follow the rules of a Punnett square.

37
Q

Are unbalanced translocation carriers usually the offspring of balanced translocation carriers or unbalanced translocation carriers?

A

Balanced translocation carriers.

38
Q

What is an unbalanced translocation?

A

A translocation in which genetic material is lost and gained.

39
Q

What determines the phenotype of an unbalanced translocation carrier?

A

The amount of material that is lost and gained.

Consider which genes are lost or gained, where they are used in the body, and how commonly they are used.

40
Q

What is a Robertsonian translocation?

A

Fusion of two acrocentric chr with loss of p arm material.

41
Q

What is the term for fusion of two acrocentric chr with loss of p arm material?

A

Robertsonian translocation.

42
Q

Is a Robertsonian translocation balanced or unbalanced?

A

Robertsonian translocations are considered balanced.

43
Q

How many chr do Robertsonian translocation carriers have?

A

45

44
Q

Why are Robertsonian translocations considered balanced?

A

They are fusions of acrocentric chr with loss of p arm material - satellites don’t contain important genetic material, so they are considered balanced.

45
Q

Which structural abnormality reduces the number of chr to 45 but is still considered balanced?

A

Robertsonian translocation

46
Q

What is the most common balanced chr rearrangement?

A

Robertsonian translocation

47
Q

How common are Robertsonian translocations?

A

1 in 1000

48
Q

Which acrocentric chromosomes can be involved in Robertsonian translocations?

A

All acrocentric chr - 13, 14, 15, 21, and 22.

49
Q

Which chromosomes can be involved in Robertsonian translocations?

A

All acrocentric chromosomes - 13, 14, 15, 21, and 22.

50
Q

Are Robertsonian translocations a numerical or a structural abnormality?

A

Both!

51
Q

What are the most important/clinically relevant Robertsonian translocations?

A

Those involving chr 21 as they are the basis of most cases of familial Down syndrome.

52
Q

What are the two possible ISCN denotations for a Robertsonian translocation?

A

der or rob

53
Q

What is the denotation for the breakpoints in a Robertsonian translocation?

A

q10

This is used as a fictional breakpoint representing the centre of the centromere.

54
Q

Why does a Robertsonian translocation reduce the chr number to 45?

A

Two acrocentric chr are fused and the two displaced satellites recombine and are lost.

55
Q

What is the karyotype of a female with a Robertsonian translocation between chr 13 and chr 14?

A

45,XX,rob(13;14)(q10;q10)
OR
45,XX,der(13;14)(q10;q10)

56
Q

What is the karyotype of a male with a Robertsonian translocation between chr 13 and chr 15?

A

45,XY,rob(13;15)(q10;q10)
OR
45,XY,der(13;15)(q10;q10)

LQB490 (2 decks)

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