Introduction to Genetics Flashcards
Describe features of autosomal dominance
- Affects males and females equally,
- Appears in multiple generations (vertical pedigree pattern),
- Disease expressed in heterozygotes,
- 50% chance of being affected,
- Variable Expressivity (Varies in severity),
- Incomplete penetrance (may have the genotype but not the phenotype)
Describe features of autosomal recessive
- Males and females equally affected.
- Usually only occurs in 1 generation (horizontal pedigree pattern),
- Diseases only expressed when homozygous or cpd heterozygotes (two mutation but different),
- 25% of being affected, 50% chance of being a carrier and 25% of neither.
- More constant expressivity,
- More common in consanguious families.
What are modifier genetic variants?
Mutations in genes other than the main gene mutated which will affect the severity or penetrance.
Name some examples of autosomal dominant conditions
- Inherited breast (BRCA)/colon cancer
- Adult Polycystic Kidney disease,
- Neurofibromatosis type 1
- Huntington’s disease
Name some examples of autosomal recessive conditions
- Cystic fibrosis,
- Phenylketonuria,
- Spinal muscular dystrophy,
- Congenital adrenal HYPERplasia,
- Wilson’s disease,
-Tay-sachs disease
What is Mosaicism
When a genetic abnormity arises during mitosis after fertilisation. So the individual has both a normal cell line and a genetically abnormal cell line.
What is Gonadal Mosaicism ?
This is when a healthy individual may have a genetic abnormality in a proportion of their germ cells. Only some cells will produce the genetic phenotype
What are the features of X-linked recessive?
- Never male-male transmission,
- ‘Knights move’ pedigree pattern,
- With an affected dad, all the daughters will be carriers
- With an affected mum, 50% of daughters will be carriers.
- Males more affected than females.
Describe features of X-linked dominant inheritance
- Never male-male transmission,
- Vertical pedigree patter,
- With an affected dad, all daughters will be affected,
- With an affected mum, 50% of daughters will be affected.
- Ration of affect is 2:1 = F:M
What are some examples of X-linked dominant inheritance?
- Vitamin D resistant rickets,
- Incontinentia pigmenti,
- Rett Syndrome
What is genetic anticipation?
A phenomena where genetic diseases increase in severity and earlier age of onset in successive generations (seen in Huntington’s)
What is pseudo-autosomal inheritance?
When a mutation occurs within the pseudoautosomal region on the short arms of the sex chromosome and is inherited in an autosomal-like fashion.
What is pseudo-dominant inheritence?
A recessive inheritance which appears dominant as so many people in the general population have the recessive gene or if there is consanguinity
What is mitochondrial inheritance?
Genetic mutations within mitochondrial DNA. Inherited only from the mother.
All children inherit the mutation but to variable extents. The syndromes often affect the muscles, brain and eyes.
