16. Cytogenetics

Question 1

What is the short arm of a chromosome known as?

Answer 1

p arm

Question 2

Long arm

Answer 2

q arm

Question 3

What is a metacentric chromosome?

Answer 3

Centromere is in the middle

Question 4

What is a submetacentric chromosome?

Answer 4

Centromere is more to one end

Question 5

What is an acrocentric chromosome?

Answer 5

DNA above the centromere doesn’t contain genes

Question 6

How do you name a part of interest on a chromosome?

Answer 6

1. Chromosome number
2. Long/short arm
3. Region
4. Band
5. Sub-band

Question 7

What is non-disjunction?

Answer 7

Failure of chromosomes to separate in mitosis or meiosis

Question 8

What happens if non-disjunction occurs within the first division of meiosis?

Answer 8

Gametes contain both parental chromosomes or neither (leads to aneuploidy)

Question 9

What happens if non-disjunction occurs within the second division of meiosis?

Answer 9

Gametes contain 2 copies of the same chromosome or neither

Question 10

What happens if non-disjunction occurs in mitosis?

Answer 10

Causes a ‘mosaic’ organism

Symptoms of disease are less severe

Question 11

What is Robertsonian translocation?

Answer 11

2 acrocentric chromosomes lose their short arms and fuse to form a single chromosome
This attracts both of the former chromosomes’ matches
Likely to cause trisomy due to uneven splitting

Question 12

Clinical indications for prenatal cytogenesis

Answer 12

1. Abnormal ultrasound
2. Advanced maternal age
3. Previous child with trisomy
4. Infertility
5. Known carrier of chromosome abnormality

Question 13

What is imprinting?

Answer 13

Different expression of same chromosomal region depending on which parent the region was inherited from
Eg. Prader Willi=paternal
Angelman=maternal