Advanced Mendelian Genetics Flashcards
What is an allele
Are different variants of the same gene
They correspond to the same region of DNA (same locus) but have some differences in base sequences
What is a dominat allele
Produces an effect on the phenotype when present in either one or two copies
What is a recessive allele
A recessive allele produces an effect only when there is no dominat allele present
What is a ‘wild-type’ of an enzyme
The allele that encodes for the normal working copy og the enzyme which is usually domiant
non-functional enzyme which code for mutant alleles are usually
recessive
In the vast majority of cases, how could an individual synthesize the mutant but the reaction can proceed as normal
In most cases having half the normal amount from one working copy of the gene is enough to allow the reaction to proceed as normal
In the same way, if there was only one gene ‘wild-type’ which coded for the functional enzyme and one gene which produced a non-functional enzyme - what would this combination of allele be called
Heterozygous
What is Haplosufficient
Having half the usual amount of the catalyst present is enough for the reaction to proceed
A mutation that results in a non-working version of a protein is usually recessive
BUT not aways and this is called…
This is called a Dominat Mutant allele
What is Haploinsufficiency
The presence of half the normal amount of a protein (from one functional allele) is not enough to give the normal phenotype
With Haploinsufficiency, a heterozygous genotype with one wild type and one mutant allele results in
Half the normal amount of protein codes
And the mutant phenotype
Heterozygotes are
Phenotypically normal but are carriers of disease - autosomal recessive disorders
What can Haploinsufficiency lead to
An intermediate phenotype ‘incomplete dominance’
For the vast majority of cases an individual will be
Haplosufficient
What is a dominat negative allele, and how do they work?
- Result from mutation that prevent the action of a protein and cause the mutant protein to inhibit the action of non-mutant molecules of the same protein inside cells
- So proteins product does not work but also prevents other normal products of the same protein from working properly
What different genes exist in mice to code for the colour of their hair
- A (agouti gene) - results in yellow bands on dark hair
- Ay (agouti gene) - in the heterozygous form results in yellow hair
- aaB (black/brown gene) - determines background colour of hairs, in this case black
- aabb - results in brown hair
- Abb - result in cinnamon hair
How is Epistasis occuring in the flower colour in sweet peas
The C gene is Epistatic over the P gene because in the presence of two recessice c alleles the effect of the P gene is hidden
Conversely the P is hypostatic to the C
What is expressivity
The degree of phenotypic change produced by a genotype, can be variable (not necessarily all or nothing)
