18. Mendelian Genetics 2

Question 1

What is X-chromosome inactivation?

Answer 1

In each cell one X chromosome is inactivated
All cells coming from that cell have the same inactivated X chromosome
Leads to ‘mosaic’ females and fully expressed males

Question 2

What is a Barr-body?

Answer 2

Dark staining mass of the inactive X-chromosome

Question 3

What is the intermediate effect?

Answer 3

50% mutated

Enough protein being made for female not to show symptoms

Question 4

What is skewed X inactivation?

Answer 4

Only 20% mutated

Normal phenotype

Question 5

What is a manifesting heterozygote?

Answer 5

80% mutated

Affected female

Question 6

Inheritance pattern of X-linked recessive disorders

Answer 6

1. No male-to-male transmission
2. Unaffected parents
3. Mother may have affected male relatives
4. Vertical pattern

Question 7

Inheritance pattern of X-linked dominant disorders

Answer 7

1. No male-to-male transmission
2. Daughters of affected males are affected
3. 50% female’s children affected
4. Vertical pattern

Question 8

Inheritance pattern of extra-nuclear inheritance

Answer 8

1. Vertical
2. Affects both sexes
3. Transmitted from mother
4. Variation of amount of abnormal DNA passed on

Question 9

Homoplasmy

Answer 9

Every cell contains mutation

Question 10

Heteroplasmy

Answer 10

Mixed population of normal and mutant genome

Question 11

What is a triplet repeat disorder?

Answer 11

Normal amount of repeated triplets repeated too many times
Expresses disease
Subtle or explosive

Question 12

What is the parent of origin effect?

Answer 12

Maternal and paternal meiosis cause different diseases

Question 13

What is anticipation?

Answer 13

Expansion of amount of repeated triplets from one generation to the next
Severity can worsen, or decreased age of onset