2 Clinical genetics Flashcards
Name the different classifications of genetic disorders
Multifactorial Single Gene Chromosomal Mitochondrial Somatic Mutations
Name the methods of single gene inheritance
Autosomal dominant
Autosomal recessive
X-linked
Mitochondrial
Autosomal dominant inheritance. Chance of offspring affected. Types of molecules affected. Examples
50%
Structural proteins, receptors, transcription factors.
Myotonic dystrophy, marfans, huntingdons, 22q11 deletion.
Define penetrance
Frequency with which a phenotype is expressed by individuals that possess it
Define expressivity
Extent to which a heritable trait is manifested by an individual - variation in expression
Define anticipation.
2 examples
Symptoms of genetic disorder start earlier with each generation.
Myotonic dystrophy. Huntingdon’s.
Describe the familial appearance of X-linked inherited conditions.
Males affected. Females may be affected, but less severely (X-inactivatoin). NO male to male transmission.
Name 3 recessive X-linked conditions.
Red-green colour blindness.
Haemophilia.
DMD.
Describe X-inactivation.
Aka lyonisation.
Random inactivation of X in cells with more than one. Compensation for double dose. Occurs in embryogenesis. Most genes switched off.
Describe how X-inactivation is linked to disease expression
Skewed X-inactivation - random preference for normal X to be silenced.
Tissue variability - random preference for mutated X to be active in crucial tissue group
Explain mitochondrial inheritance.
All mitochondria from mother.
M+F equally affected.
27 genes in mitochondrial DNA.
Highly variable expressivity.
Draw the pedigree symbols for male, female, miscarriage, terminated pregnancy and monozygotic twins
Square. Circle. Pyramid. Pyramid with line through. Cherry branch with horizontal line.
Name two dominant X-linked conditions.
Rett syndrome (lethal to males). Fragile X.
Name two mitochondrially inherited conditions.
Maternally inherited diabetes and deafness.
