Week 106 - Introduction to Medical Genetics Flashcards
What is loci?
Location of a gene on a chromosome
What is an allele?
Alternative copy of the same gene
- i.e. one gene is maternal and it’s allele is paternal
What is penetrance?
Proportion of individuals who carry a gene (mutation) that will display the phenotype
What are single gene disorders?
Disease caused by a mutation at a single gene loci
What is an autosomal dominant disease?
Gene mutation on a non-sex chromosome
Only need to get the gene from one parent
Not possible to be a carrier without the disease
50% chance that offspring will be affected
Give examples of autosomal dominant conditions?
Huntington disease - chromosome 4
Marfan syndrome
Familial hypercholesterolaemia
Familial adenomatous polyposis - APC gene
Long QT syndrome - prolonged QT interval
Breast cancer
What is an autosommal recessive condition?
Gene mutation on a non-sex chromosome
Both parents have to be carriers
Normally: 25% chance offspring will be affected
- i.e. Rr * Rr
Consanguinity will increase risk in offspring
Give examples of autosomal recessive conditions?
Cystic fibrosis
Phenylketonuria
Beta-thalassemia
Sickle cell anaemia
Tay sachs disease
Spinal muscular atrophy
What is an X-linked recessive condition?
Gene mutation on the X-chromosome
Males much more likely to be affected
- females would need two of the mutated genes
Father is unaffected (Y, Xo), mother is carrier (Xo,Xr)
25% chance of having an affected son
Give examples of X-linked recessive conditions?
Duchenne muscular dystrophy
Haemophilia A
Red-green colour blindness
What is an X-linked dominant condition?
Dominant gene mutation on the X chromosome
Father or mother is affected and the other is unaffected
50% chance of having an affected offspring
Give an example of an X-linked dominant condition
Charcot-marie-tooth disease
What are multifactorial disorders?
Disorders caused by multiple genes in combination with environmental factors
i.e. environment exposure to susceptible individuals
Give examples of multifactorial disorders
Type II diabetes mellitus
Essential hypertension
What are chromosome disorders?
Caused by aneuploidy (loss or gain) in one or more chromosomes
