Autosomal Recessive Disorders

Question 1

How do you recognise ARD from phenotype

Answer 1

Cant follow disease through pedigree
Within 1 generation
Equal incidence of males and females
Evidence of consanguinity

Question 2

What is Pseudodominance

Answer 2

When ARD appears in subsequent generations

Question 3

What is the Hardy Weinberg Principle

Answer 3

p = dominant 
q = reccesive 
p^2 = homozygous dominant 
q^2 = homozygous recessive 
2pq = heterozygous

Question 4

How do we apply the Hardy Weinberg Principle and what are the conditions

Answer 4

Relative proportions of each genotype will remain constant in subsequent generations
Conditions = random mating, infinitely large pop, no preferential selection of genotypes, no new alleles

Question 5

How do we determine risk of other family members for disease

Answer 5

Screen affected and determine mutation

Screen other family members and see if they have same mutation

Question 6

What are the determinants of genotype frequency in population

Answer 6

New mutation rate
Heterozygous advantage = Aa adv. over AA
- Sickle cell gene resistant to malaria

Question 7

What are the methods analysis for parental diagnosis

Answer 7

Mutation analysis = gene tracking

Linkage analysis = when we dont know what mutation is. Label whole genes and compare affected with unaffected

Question 8

What is genetic heterogeneity

Answer 8

Defects in more than 1 gene account for disorder

Question 9

What is an example of a ARD?

Answer 9

Cystic Fibrosis
Production of very thick mucus that clogs lungs
Mutation in CFTR gene - 3BP deletion + CG accumulation upstream of gene coding regions