L3 Relationship Between Genotype And Phenotype Flashcards
The relationship between genotype and phenotype is affected by…
- Penetrance and expressivity
- pleiotropy and epistasis
- environmental effects
- complementation
( in addition to dominant/recessive relationship between alleles )
Linkage is the presence of genes…
On the same piece of DNA
Genetic maps map the genome using…
frequency of recombination to determine distance between genes
Dominance relationships can be either (3)…
Complete, incomplete or codominant
Pleiotrophy
When a single gene affects multiple unrelated characteristics
An example of pleiotrophy is…
Manx cats. The pleiotropic gene affects both tail and spinal development. Heterozygosity results in no tail, homozygotes do not survive
Epistasis
When one mutation hides or modifies the phenotype at another gene
The same genotype ( always / does not always ) lead to the same phenotype
Does not always
Penetrance is the degree to which…
A particular genotype, when present, results in the characteristic phenotype within a population
Penetrance is either…
Complete (100%) or incomplete (<100%)
In many diseases, the same gene mutation can result in a variety of symptoms in different individuals. This can be explained by variable…
Expressivity (or a spectrum of expression)
The difference between penetrance and expressivity is that…
Penetrance is how many show the trait at all, whereas expressivity is the degree and nature of the traits expression
Complementation
When different mutations at different genes partly or entirely cancel each other out if they cooccur
An example of environmental effects on phenotype is…
Siamese cats which have brown colour on the extremities because the protein responsible only works at lower than normal body temperature.
Recombination frequency =
( recombinants / total ) x 100
cM
centiMorgan (or more commonly map units, mu)
If two genes are unlinked, when crossing a hybrid (F1) with a homozygous mutant type the offspring are expected to be…
50% parental, 50% recombinant
When two genes are linked, we get…
More parental combinations (less recombination)
The lower the frequency of recombination…
The closer the genes on a chromosome
Genetic maps are not colinear with physical maps. This is because recombination…
Is not random- there are hotspots, which means physical distances doesn’t always correspond to cM distance shown by genetic maps
Test crosses for 2 traits can be used to assess…
Gene linkage
