X-linked Inheritance

Question 1

T or F: an affected male can pass the disease to his son in x-linked recessive diseases

Answer 1

FALSE

Question 2

If a male has an x-linked recessive disease, what is the chance that his daughters will be carriers?

Answer 2

100%

Question 3

If a female is a carrier of an x-linked recessive disease, what are the chances of her daughter carrying it?

Answer 3

50%

Question 4

If a female is a carrier of an x-linked recessive disease, what are the chances of her son having it?

Answer 4

50%

Question 5

What is the only non-homologous chromosome pair in the body?

Answer 5

XY

Question 6

T or F: an offspring with the genotype XO is a male

Answer 6

False - Y is the male determining chromosome

Question 7

What is PAR?

Answer 7

The pseudoautosomal region on the X and Y chromosomes

Question 8

What is the job of PAR?

Answer 8

promotes sex chromosome pairing in prophase I of male meiosis

Question 9

What process allows females to achieve dosage compensation?

Answer 9

x inactivation allows matching between the number of gene products present in males and females

Question 10

What chromosomes in the body are most prone to nondisjuction issues?

Answer 10

XY

Question 11

T or F: the X in sperm must come from the mother

Answer 11

T

Question 12

T or F: X chromosome in female sex cells must be from mother

Answer 12

F - its has equal chance of being paternal or maternal

Question 13

When does x-inactivation occur

Answer 13

at around 40 or 50 cells (7-10 days)

after this point the pattern is fixed

Question 14

T or F: the initial decision of what x chromosomes to turn off is random

Answer 14

T

Question 15

T or F: females will never display mild phenotypic consequences of an x-linked recessive mutation

Answer 15

False - x inactivation may be skewed leading to a mild phenotype

Question 16

What is XIST?

Answer 16

• Gene on the Barr Body and ONLY on the Barr Body that produces NON-coding RNA
• RNA coats the chromosome marking it as inactive

Question 17

T or F: no gene on the barr body escapes x inactivation.

Answer 17

False - 15 -20% genes escape x inactivation

Question 18

What is the region where the genes escaped deactivation on the barr body called?

Answer 18

pseudoautosomal region

Question 19

T or F: it is an epigenetic process that achieves dosage compensation

Answer 19

True

Question 20

What happens to the barr body in germline cells?

Answer 20

It is decondensed

Question 21

What are four examples of x-linked recessive disorders?

Answer 21

1. Duchenne & Becker muscular dystrophy
2. Hemophilia A
3. Red green colorblindness
4. G6PD

Question 22

What are 3 examples of x-linked dominant disorders?

Answer 22

1. hypophyosphatemic rickets
2. Rett Syndrome
3. Incontinentia pigmenti type 1

Question 23

What is the disease risk to a son whose father has hemophilia A?

Answer 23

none

Question 24

When can a women be determined an obligate carrier of an autosomal recessive disease?

Answer 24

• affected brother and affected son

- two or more affected sons

Question 25

What is a simplex case?

Answer 25

a case that may either be a new mutation or an inherited mutation

Question 26

What is an example of a simplex case with hemophilia A

Answer 26

single affected family member