Numerical and structural abnormalities

Question 1

What is aneuploidy?

Answer 1

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

Question 2

What gives rise to aneuploidy?

Answer 2

Non-disjunction

Question 3

What is non-disjunction?

Answer 3

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

Question 4

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

Answer 4

Monosomy and trisomy cell lines.

Question 5

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

Answer 5

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

Question 6

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

Answer 6

Mosaicism

Question 7

What is mosaicism?

Answer 7

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

Question 8

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

Answer 8

Meiosis

Question 9

Approximately how many conceptions are monosomic or trisomic?

Answer 9

25%

Question 10

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

Answer 10

Segregation

Question 11

Scenario: all four gametes produce a child.

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

Answer 11

No normal, two trisomy, two monosomy.

Question 12

Scenario: all four gametes produce a child.

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

Answer 12

Two normal, one trisomy, one monosomy.

Question 13

What is the ISCN denotation for a translocation?

Answer 13

t

Question 14

What is a translocation?

Answer 14

A two-way exchange of material between two chromosomes.

Question 15

What is the most common type of translocation?

Answer 15

Balanced reciprocal translocation

Question 16

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

Answer 16

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

Question 17

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

Answer 17

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

Question 18

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

Answer 18

No (not necessarily)

Question 19

How common are translocations in the normal population?

Answer 19

1 in 600

Question 20

How does a reciprocal translation occur?

Answer 20

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

Question 21

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?

Answer 21

Translocation

Question 22

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

Answer 22

Translocated segments

Question 23

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

Answer 23

Centric segment

Question 24

What is a centric segment?

Answer 24

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

Question 25

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

Answer 25

Derivative chromosome (der).

Question 26

What is the ISCN denotation for a derivative chromosome?

Answer 26

der

Question 27

What is a derivative chromosome?

Answer 27

A rearranged chromosome following translocation.

Question 28

How are derivative chromosomes identified?

Answer 28

By which centromere it possesses.

Question 29

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

Answer 29

Derivative chromosome

Question 30

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

Answer 30

der(5)

Question 31

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

Answer 31

der(10)

Question 32

Do balanced translocation carriers display phenotypical abnormalities?

Answer 32

No

Question 33

Do unbalanced translocation carriers display phenotypical abnormalities?

Answer 33

Yes

Question 34

What type of issues do balanced translocation carriers often have?

Answer 34

Fertility issues, often involving multiple consecutive miscarriages.

Question 35

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

Answer 35

Yes

Question 36

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?

Answer 36

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.

Question 37

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

Answer 37

Balanced translocation carriers.

Question 38

What is an unbalanced translocation?

Answer 38

A translocation in which genetic material is lost and gained.

Question 39

What determines the phenotype of an unbalanced translocation carrier?

Answer 39

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.

Question 40

What is a Robertsonian translocation?

Answer 40

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

Question 41

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

Answer 41

Robertsonian translocation.

Question 42

Is a Robertsonian translocation balanced or unbalanced?

Answer 42

Robertsonian translocations are considered balanced.

Question 43

How many chr do Robertsonian translocation carriers have?

Answer 43

45

Question 44

Why are Robertsonian translocations considered balanced?

Answer 44

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

Question 45

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

Answer 45

Robertsonian translocation

Question 46

What is the most common balanced chr rearrangement?

Answer 46

Robertsonian translocation

Question 47

How common are Robertsonian translocations?

Answer 47

1 in 1000

Question 48

Which acrocentric chromosomes can be involved in Robertsonian translocations?

Answer 48

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

Question 49

Which chromosomes can be involved in Robertsonian translocations?

Answer 49

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

Question 50

Are Robertsonian translocations a numerical or a structural abnormality?

Answer 50

Both!

Question 51

What are the most important/clinically relevant Robertsonian translocations?

Answer 51

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

Question 52

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

Answer 52

der or rob

Question 53

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

Answer 53

q10 This is used as a fictional breakpoint representing the centre of the centromere.

Question 54

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

Answer 54

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

Question 55

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

Answer 55

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

Question 56

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

Answer 56

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