Advanced Mendelian Genetics 2 Flashcards
Define epistasis and explain it using an example Give some specific examples of modifier genes and discuss their general importance in genetics Describe the genetic effects of penetrance and expressivity using Huntington's disease as an example Explain what a genetic map is, the nature of genetic linkage and recombination, and how by measuring recombination we can produce genetic maps
Define epistasis:
The interaction of genes that are not alleles, in particular the suppression of the effect of one such gene by another.
What is a hidden gene called and how does this occur?
The hidden gene is hypostatic to the other gene which is epistatic, effect of a gene at a different gene locus
What is an example of epistasis?
Coat colour and appearance in mice
In mouse coats, what are the modifier genes?
D - full colour
S - No spots
W - lethal or white spots
What is a modifier gene?
They do not hide the effect of colour genes but modify the phenotype produced
How does epistasis work?
Epistatic interactions can occur when the genes involved encode enzymes in the same biological pathway
What is penetrance?
Penetrance is the probability that an individual with an appropriate genotype will show a change in phenotype
What is expressivity?
Degree of phenotypic change produced by a genotype, can be variable
What is Huntington’s disease and how genetically does it occur? (5)
Disease of the mind and the body - sex chromosome mutation Autosomal dominant Variable expressivity Incomplete penetrance Variable age of onset
What are the symptoms of Huntington’s disease: (4)
Lack of co-ordination, tremors, mood swings
Twitching, depression
No cure
Gradual decline
What is the HD gene?
Chromosome 4 - encodes Huntington
What is a genetic map?
Based in mapping genes relative to each other or another feature of the genome
Produced by observing the outcome of crosses, genetic linkage and recombination frequency
What is linkage?
Alleles of genes that are close together on the same chromosome tend to be passed on together to offspring
What is recombination?
Recombination opposes linkage
When the chromosomes pair during meiosis (to form the gametes) pieces of DNA get swapped between them which mixes up the combinations of alleles
