Genetic Diseases Flashcards
Give three broad causes of disease.
Genetic e.g. Cystic fibrosis
Environmental - main cause of death in third world countries e.g. infection
Multifactorial - main cause of disease in developed countries e.g. diabetes
What term is given to the position of a gene?
Locus
Which chromosomes are autosomal?
1-22.
What is a genotype?
Genetic constitution of a person.
What is a phenotype?
Appearance of an individual as a result of their genotype.
What is the term given to alternative forms of a gene at a specific locus?
Allele
What is a normal allele called?
Wild type
What is polymorphism?
Frequent hereditary variations at a locus. Can make you more or less susceptible to a disease.
What is the term given to two relatives who reproduce?
Consanguinity
What does homozygous mean?
Both alleles are at the same locus
What does heterozygous mean?
Alleles at a locus are different.
Which term refers to genes being carried on an unpaired chromosome - i.e. a locus on an X chromosome in a male?
Hemizygous
What does penetrance mean?
Proportion of people with a gene who show the expected phenotype
Which term is given to the fact that there is variation in clinical features between patients of a genetic disorder?
Variable expression
If a multifactorial condition is more common in males, which relatives (in terms of sex) will have a higher risk?
The female relatives
What does congential mean?
Condition manifested at birth
Which pattern of inheritance results in disease only manifesting if in the heterozygous state?
Autosomal dominant. One defective gene required.
What is the only pattern of inheritance that allows disease to be passed from male to male?
Autosomal dominant
When would parents be unaffected by an autosomal dominant disease?
- Don’t have genes for it
- Gonadal mosaicism
- Mother has reduce penetrance or variable expression
What is autosomal recessive inheritance?
A disease that manifests in the homozygous state. Two defective genes required.
What % chance will the offspring have the condition and be a carrier if the parents are carriers?
25% chance offspring having condition
2/3 chance offspring will be a carrier
What is the most common autosomal recessive condition affecting whites in the UK?
Cystic fibrosis. Incidence = 1 in 25,000
Who should you disregard when calculating risk of carriers in offspring?
The already affected child. If one child is unaffected, one is affected and 2 are carriers, then the chance of being a carrier is 2/3 NOT 1/2.
What causes X-linked inheritance?
A mutation in genes on the X chromosome.
