Chromosomal Anomalies - Structure

Question 1

Which chromosomes are acrocentric?

Answer 1

13, 14, 15, 21, 22.

Question 2

What is chorionic villus sampling?

Answer 2

The sampling of tissue from the villus of a chorion (outermost membrane of an embryo) at ~11 weeks of pregnancy.

Question 3

Why might a family wish to take fetal karyotyping if a robertsonian translocation is suspected?

Answer 3

To determine whether the baby has the normal pattern of chromosomes, the balanced or unbalanced form.

Question 4

How might a partial aneuploidy arise?

Answer 4

From inheriting one of the products of a reciprocal translocation (not both - this would be balanced).

Question 5

List 4 symptoms and complications of partial aneuploidies.

Answer 5

1 - Miscarriage.

2 - Congenital malformation.

3 - Developmental delay.

4 - Intellectual disability.

Question 6

What is the most likely cause of two children (separate births) being born with a chromosomal deletion or duplication (genetic defect not caused by translocation) where the parents are not carriers (arose during meiosis).

Answer 6

• Chromosomal deletions and duplications are usually one off events in meiosis and are rare.
• Recurrence suggests it is not by chance, so is likely due to gonadal mosaicism (mutation occurred to gonadal stem cell).

Question 7

List 3 different patterns of chromosomes that can cause down syndrome.

Answer 7

1 - Possessing three separate copies of chromosome 21.

2 - Possessing three copies of chromosome 21 due to a Robertsonian translocation.

3 - Mosaicism causing some cells to possess 3 copies of trisomy 21 and others to be normal.

Question 8

How does mosaicism arise?

Answer 8

A mutation is introduced postzygotically (de novo) to a stem cell.