Week 106 - Introduction to Medical Genetics Flashcards Preview

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Flashcards in Week 106 - Introduction to Medical Genetics Deck (18):

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



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


Give examples of chromosome disorders

Trisomy 21 - an extra chromosome 21

Turners syndrome - X => gonadal dysgenesis

Klinefelters syndrome - XXY => hypogonadism + sterility


What are somatic cell gene disorders?

Mutations only in cells of the same lineage

- i.e. tumour cell that contains a mutated gene that is passed onto daughter cells


What are mitochondrial disorders?

Mutations in mitochondrial DNA
=> maternally inherited as sperm cell mitochondria don't enter the egg