17. Mendelian Genetics 1

Question 1

What is autosomal dominant inheritance?

Answer 1

The gene is expressed in heterzygotes

Homozygous individuals have stronger symptoms

Question 2

What is the inheritance pattern for autosomal dominant diseases?

Answer 2

1. Vertical (affected have affected parents)
2. Even split between sexes
3. Transmitted by both sexes
4. Half of affected parent’s offspring are affected

Question 3

What are the exceptions to the AD inheritance pattern?

Answer 3

1. Mutations
2. Variable expressivity
3. Reduced penetrance

Question 4

How can mutations cause phenotype?

Answer 4

1. Haploinsufficiency
2. Dominant negative effect
3. Gain of function
4. Loss of heterozygosity

Question 5

What are autosomal recessive disorders?

Answer 5

Symptoms only show in recessive homozygotes

Heterozygous individuals at no selective disadvantage

Question 6

Autosomal recessive inheritance pattern

Answer 6

1. Limited to one ‘sib-ship’
2. Horizontal
3. Even between sexes
4. Consanguity

Question 7

How can AR diseases be identified?

Answer 7

1. Newborn screening programmes
2. Multiple affected siblings
3. Consanguity
4. Partial defect in parents

Question 8

What is genetically heterogeneity

Answer 8

Same clinically diagnosed disease is caused by different DNA sequence defects

Question 9

PKU: What type of genetic heterogeneity
What type of disease
What happens

Answer 9

1. Allelic
2. Autosomal recessive
3. PAH gene converts phenylalanine to tyrosine
   Can happen in various places, phenotype depends on where they occur

Question 10

What is retinitis pigmentosa and what 3 types of mutation contribute to the phenotype

Answer 10

Progressive visual loss

AD, AR, X-linked