Genetics 2

Question 1

In notes how are the short arm and long arm of chromosomes written as?

Answer 1

p = short arm and q = long arm

Question 2

What is an acrocentric chromosome? and what chromosomes are acrocentric?

Answer 2

Chromosomes what don’t really have a short arm. These are chromosomes 13, 14, 15, 21 and 22

Question 3

What is balanced chromosome rearrangement?

Answer 3

Where all chromosomal material is present but it just isn’t in the correct place

Question 4

What is unbalanced chromosomal rearrangement

Answer 4

Extra or missing chromosomal material, usually 1 or 3 copies of some of the genome.

Question 5

What is aneuploidy?

Answer 5

A whole extra chromosome or a missing chromsome

Question 6

What is 47 XY + 21

Answer 6

A boy who has trisomy 21 which results in down syndrome. The 47 means 47 chromosomes

Question 7

What is 47 XY + 18

Answer 7

A boy who has trisomy 18 resulting in Edward syndrome

Question 8

What is 47 XX + 13

Answer 8

A girl who has trisomy 13 resulting in Patau syndrome

Question 9

What are some of the rapid prenatal diagnosis of genetic disorders

Answer 9

Interphase chromosome counting using FISH (fluorescence In Situ Hybridisation) or comparative genome hybridisation

Question 10

What is 45 X

Answer 10

A girl with turner syndrome

Question 11

What aneuploidy’s are better tolerated?

Answer 11

X chromosome aneuploidy due to X inactivation

Question 12

Describe chromosomal insertions

Answer 12

This is a genetic mutation where part of one chromosome is cut out and gets inserted into another chromosome. Only symptomatic if it cuts through a gene.

Question 13

What is Robertsonian Translocation

Answer 13

When two acrocentric chromosomes are stuck end to end. (look at an image)

Question 14

What can result from Robertsonian translocation?

Answer 14

An increased risk of trisomy in pregnancy (50%)

Question 15

What is 46 XY, der (14;21) + 21

Answer 15

A boy with 46 chromosomes with an inherited (der = derived) robertsonian translocation where an chromosome 21 joined onto chromosome 14 and counted as 1 whole chromosome. Therefore he has three 21 chromosomes worth of genetic material.

Question 16

What is a reciprocal translocation

Answer 16

The exchange of two acentric fragments (chromosome lacking centromere) and this can occur with any autosomal chromosmes

Question 17

Explain 46, XX, t(12;17)(p13;p13)

Answer 17

A woman with a translocation between chromosomes 12 and 17. At the short arm position 13 on both.

Question 18

Explain 46, XY, der(17)t(12;17)(p13;p13)mat

Answer 18

A son who inherited chromosme 17 which has a translocation from chromosme 12 on the short arm at position 13.

Question 19

What are the reproductive risks with reciprocal translocations

Answer 19

50% normal/balanced and 50% unbalanced. Unbalanced results in miscarriage (large segments) or dysmorphic delayed child (small segments)

Question 20

What is a Philadelphia chromosome?

Answer 20

This is a reciprocal translocation between chromosomes 9 and 22 that can happen to anyone

Question 21

What is the clinical significance of philadelphia chromosome

Answer 21

95% of patients with chronic myeloid leukaemia have this genetic mutation

Question 22

What are some single chromosome mutations?

Answer 22

1. Deletion.
2. Duplication.
3. Inversion