Phenotypic variability Flashcards
What effects phenotypic variability?
Environmental impact. Sex. Effect of other genes. Different mutation in same gene. Unstable mutations such as tri-nucleotide repeat expansions.
What in a trinucleotide repeat expansion affects phenotype severity.
More repeats more severe phenotype.
What happens to tri-nucleotide repeat expansions down generations?
Increases.
If a disease is present in an extended family what is unlikely to occur that could affect phenotypic variability?
The family members have inherited different mutations.
If a disease is present in an extended family what is likely to occur that could affect phenotypic variability?
A second gene modifies the disease phenotype.
If a disease is caused by an unstable trinucleotide repeat and there is phenotypic variability across generations what could explain this?
Environmental factors can modify the disease phenotype.
If there is wide phenotypic variability between families with ‘same disease’ what is most likely to explain for this?
Different mutation in same gene.
If there is no phenotypic variability in a disease between monozygotic twins but there is genetic variability in non monozygotic twins what does this tell us?
Must be a genetic basis driving phenotypic variability.
If there is a wide variability of symptoms both within affected families and between affected families and no variability in monozygotic twins what is most likely to explain this?
Second gene modifying phenotype.
A disease is caused by mutation in mitochondrial DNA, the severity of the disease and age of onset is highly variable, what is the most likely explanation for this?
A variable number of mitochondria with the mutation are inherited.
Several members of an extended family have a disease. Age of onset and severity of the disease shows marked variability with no two members being affected in the same way.
Because no two members are affected in the same way environmental factors are the most likely explanation. A second gene affecting phenotype is possible but not the most likely given the marked variability.
Severity of trinucleotide repeat disorders down generations?
Increases as you have expansion of unstable trinucleotide repeat as you go down generations.
