Mendelian Inheritance Flashcards
Types of genetic disorder
- Single gene disorder
- Multifactorial/common complex disorder
- Chromosome disorder
- Mitochondrial disorder
- Somatic mutation
Types of single gene disorder
- Dominant
- Recessive
- X-linked (D+R)
Exceptions to Mendel’s rules in autosomal dominant inheritance
- Variation in expression
- Reduced/incomplete penetrance (+ age-dependent penetrance)
- New mutation
- Anticipation
- Mosaicism
What is anticipation?
Due to unstable trinucleotide repeat mutations expanding, age of onset is reduced and severity of phenotype is increased in successive generations
How can you recognise an autosomal recessive disease from a pedigree?
- Can’t follow the disease through the pedigree
- See siblings affected (horizontal transmission)
- Equal incidences of male + female
- May be evidence of consanguinity
What must be present for the Hardy-Weinberg principle to hold true?
- Random mating
- Infinitely large population
- No preferential selection of genotypes
- No new alleles
Why do some females show X-linked recessive traits?
- Skewed X-inactivation
- Turner syndrome (45,X)
- Homozygous recessive trait
- X;autosome translocations
How can an X-linked dominant disease be distinguished from an autosomal dominant in a pedigree?
- Excess of affected females
- No male to male transmission
Why is mitochondrial inheritance only maternal?
Sperm mitochondria are expelled from the fertilized egg
What proportion of offspring from an affected male and female would be affected through mitochondrial inheritance?
- Male = 0%
- Female = 100%
