DLA 13

Question 1

Describe the characteristics of X-linked recessive disorders?

Answer 1

skipping of generations

NO male to male transmission

found in males more often

Question 2

Duchenne Muscular Dystrophy (DMD)

Answer 2

tends to be lethal before the age of 30

enlarged calves and wasting of thigh muscles

Do not have children

X-linked recessive disorder

Question 3

Becker muscular dystrophy

Answer 3

Same mutation found in DMD

Becker is a less severe mutation compared to duchenne

for example, BMD can have children

Question 4

Hemophilia A

Answer 4

inherited deficiency of the clotting factor VIII, thus there is an increased tendency to bleed after minor traumas.

is caused by incorrect splicing

does show allelic heterogeneity

Question 5

X-linked SCID

Answer 5

Caused by a defective gamma chain of the receptor for several different interleukins

T-cells are not able to mature, thus no immune function

SCIDX1 gene mutation

Question 6

Manifestations in a female typically are due to?

Answer 6

skewed or asymmetric X-inactivation

Question 7

Red/green color deficiency?

Answer 7

An example of a non-lethal sex-linked trait

Question 8

Example of an X dominant disorder?

Answer 8

Rett syndrome

affects females more than males

however, males with this mutation normally die during pregnancy or right after birth

Question 9

Incontinentia pigmenti?

Answer 9

An x-linked dominant disorder that is lethal to males

Males usually die in utero

variable expresstivity in females due to X-inactivation

Question 10

Symtpoms of Incontinentia pigmenti?

Answer 10

rashes and blisters early in life

hyperpigmentation

intellectual disability

retinal detachment (in some)

Question 11

More examples of X-linked dominant disorders?

Answer 11

1. vitamin D resistant rickets
2. rett syndrome (lethal in males)
3. incontinentia pigmenti (lethal in males)

Question 12

What is incomplete penetrance?

Answer 12

When an individual has an allele for a certain illness but does not show symptoms

Question 13

What is full penetrance?

Answer 13

All those that have the mutated allele will show symptoms of that disorder

Question 14

What is a general example of incomplete penetrance?

Answer 14

age-dependent penetrance

delayed onset

Question 15

some people are heavily impacted and some are mildly impacted by a mutated allele why?

Answer 15

1. random chance
2. other genetic factors (sex)
3. environmental factors

Question 16

Example of variable expression?

Answer 16

hemochromatosis

males are more impacted than females due to gender.

males are not able to remove iron while females can

Question 17

What is the meaning of pleiotropy?

Answer 17

This is a disorder where more than one organ system is impacted

Ex: marfan syndrome and osteogenesis imperfecta

Question 18

What is locus heterogeneity?

Answer 18

mutations at different loci that cause the same disease

mutations of different genes that cause the same disease

Question 19

Example of locus heterogeneity?

Answer 19

osteogenesis imperfecta - mutation at gene 17 or 7?

Question 20

Explain breast cancer susceptibility genes?

Answer 20

BRCA1 and BRCA2

both of these genes are located at different chromosomes but they have a similar phenotype

Question 21

Does charcot-Marie-Tooth disease show locus heterogeneity?

Answer 21

Yes, multiple genes are known that can lead to this disorder

Question 22

Locus heterogeneity VS allelic heterogeneity

Answer 22

Locus = mutations of different genes that lead to the same disease state

Allelic = different mutations on the SAME gene