Lecture 15 - Errors in Meiosis & X-inactivation

Question 1

What are the types of chromosomal abnormalities? (6)

Answer 1

• Nondisjunction
• Aneuploidy
• Deletion
• Duplication
• Inversion
• Translocation

Question 2

What is Aneuploidy and give three examples?

Answer 2

Abnormal number of a
particular chromosome

E.g down syndrome, trisomy 21 (3 21 chromosomes)

E.g Klinefelter syndrome; extra sex chromosome (XXY)

E.g. Turner syndrome; only one sex chromosome (XO)

Question 3

What is Non-disjunction?

Answer 3

Failure of chromosomes
to separate properly
during meiosis

Question 4

How does non-disjunction lead to down syndrome?

Answer 4

95% of Down syndrome babies have two maternal chromosome 21, leading there to be 2 maternal and 1 paternal chromosome 21.

Question 5

If a pair of chromosomes fails to disjoin at anaphase of meiosis I, what will be the likely chromosome numbers (N) of the four resulting gametes?

A. N+1, N+1, N, N.
B. N+1, N+1, N-1, N-1.
C. N+1, N-1, N, N.
D. N, N, N-1, N-1

Answer 5

N+1, N+1, N-1, N-1.

Question 6

What is polyploidy?

Answer 6

Possession of multiple sets of chromosomes

Question 7

What is allopolyploidy?

Answer 7

2 total sets of chromosomes

Question 8

What is triploid?

Answer 8

3 total sets of chromosomes

Question 9

What is deletion? Give an example

Answer 9

Removal of chromosomal segment

E.g. Lejeune syndrome, deletion of tip in chromosome 5

Question 10

What is inversion? What does it lead to?

Answer 10

Reverses a segment within a chromosome, leads to large duplication or large deletion

Question 11

What is translocation? Give three examples

Answer 11

Moves a segment from one chromosome to a nonhomologous chromosome

E.g. Familial down syndrome; chromosomes together combine to give extra “21” chromosomes

E.g. Philadelphia Translocation t(9;22):

E.g. TK Overexpression:

Question 12

Individuals with familial Down Syndrome have which of the following karyotypes?

A) 47 chromosomes; trisomy 21.
B) 46 chromosomes; translocation of 21.
C) 46 chromosomes; inversion of 21.
D) 45 chromosomes; monosomy 21.

Answer 12

B) 46 chromosomes; translocation of 21.

Question 13

Chromosomal non-disjunction is a major cause of:

(A) X inactivation.
(B) familial Down syndrome.
(C) genetic differences between siblings.
(D) Turner syndrome.

Answer 13

(D) Turner syndrome.

Question 14

What are the consequences of x-inactivation?

Answer 14

Random inactivation of X chromosomes leads to mosaic
patterning

Question 15

An XXY human will:

A) exhibit Turner syndrome.
B) have a Barr body in each nucleus.
C) be an abnormal female.
D) be a monosomic.

Answer 15

C) be an abnormal female.

Question 16

A female is colour blind in one eye only. Her father is colour blind in both eyes. The cause of the female’s condition could be:

A) X-inactivation in a heterozygote.
B) a somatic mutation.
C) damage to one eye.
D) any of the above.

Answer 16

D) any of the above.