Module 3 Flashcards
What are intra allelic effects?
The effect of an allele on a protein
What are inter allelic effects?
The affect of other genes influencing it
What is gene action?
From genotype to phenotype
What is the agouti gene?
Encodes to signal peptide for colour and lipid metabolism
Lethal gene example
The agouti gene
Are mutations of haplosufficient genes recessive or dominant?
Recessive
What is an allelic series?
Most common allele for a locus in nature arbitrarily referred to as wild-type, often dominant
If an allele is not wild-type, what is it considered?
Considered a mutant
What does an allelic series describe?
Dominance hierarchy of multiple alleles
What is the function of a null allele?
It does not have a function
What is hypomorphic allele function?
It has a partial function
What is incomplete dominance?
Appearance of third phenotype that blends two parental ones, no clear dominance in heterozygote, blending
What is codominance?
More than one allele is dominant, heterozygote displays both parental phenotypes, shows both
What kind of relationships are codominance and incomplete dominance?
Non- Mendelian relationships
Incomplete dominance example in humans
Skin pigmentation
Codominance example in humans
ABO blood type
What kind of gene causes blood type in humans?
I gene
What is variable/incomplete penetrance?
The proportion of individuals of the same genotype that will either express determined phenotype or not express it at all, only some percentage of people show the trait
Example of variable penetrance in humans
Retinoblastoma and polydactylyl
What is variable expressivity?
Degree or intensity with which a genotype is expressed, all show the consequences but not to full extent just to a degree of severity
Examples of variable expressivity in humans
Marfan syndrome
Is it possible to have both variable penetrance and variable expressivity?
Yes
What is an example of variable penetrance and variable expressivity in humans?
Neurofibromatosis
What is pleiotropy?
One allele, affecting two or more phenotypes
What is polygenic inheritance?
Many genes and alleles, affecting the same phenotype
What are some qualitative phenotypes?
Height, skin colour, weight, intelligence, behavioural phenotypes
What are complementation tests?
Based on that wild-type alleles will make up for mutated ones of a given gene
What is allelism?
When mutations are alleles of same gene
What does complementation indicate?
Non-allelic mutants - when more than one gene is responsible to same phenotype
Are allelic mutations complementing or non-complementing?
Non-complementing
Are non-allelic mutations complementing or non-complementing?
Complementing
What are allelic mutations?
Where no functional gene 1 is synthesized in trans heterozygote; thus it will have mutant phenotype
What is a trans-heterozygote for allelic mutations?
Mutations in one gene
What is a trans-heterozygote for non-allelic mutations?
Mutations in two genes
What is a non-allelic mutation?
functional products of both genes are synthesized in the trans heterozygote, wild-type phenotype
What is molecular basis of genetic complementation?
Colour carried on different genes and can reappear, not dominant or recessive
What are auxotrophs?
Mutants that need supplementation
Are genes functionally isolated units?
No
How are genes organized?
Genes are hierarchically organized to perform function (influence phenotype) and most phenotype are polygenic
What are suppressor mutations?
A mutations that reverts the phenotypic effects of an original mutation
What is an enhancer mutation?
A mutation in a gene that enhances the phenotype caused by a mutation in another gene
What are the 3 levels of expressivity?
1) Allelic interaction (intra-genic)
2) Allele interaction with environment
3) Gene interaction
What is allelic interactions?
Dominance, recessiveness, codominance, incomplete dominance
What is gene interaction?
How alleles in different loci interact with one another to impact phenotype, reflects genetic organization in pathways controlling specific phenotypes
What are gene interaction processes/examples?
- additive gene action
- complementary gene action
- duplicate gene action
- dominant epistasis
- recessive epistasis
What is the most obvious evidence of gene interaction?
The skewing of Mendelian ratios
Additive gene action ratios
1 trait, 2 loci, 4 phenotypes
Complementary gene action ratios
2 loci, 1 trait, 2 phenotypes
Redundancy is also known as
Duplicate gene action
Redundancy ratios
2 loci, 1 trait, 2 phenotypes
Recessive epistasis ratios
2 loci, 1 trait, 3 phenotypes
Dominant epistasis ratios
2 loci, 1 trait, 3 phenotypes
What is additive gene action?
Alleles of both genes influence the same phenotype , F1 has different phenotype than parentals
Additive gene action expected ratio?
9:3:3:1
What is complementary gene action?
Genes acting in the same pathway, homozygous for either mutation, identical mutant phenotype
Complementary gene action phenotypic ratio
9:7
What explains complementary gene action?
Genes have the same linear pathway - downstream gene function fully depend on function of upstream gene
What is redundancy?
Dominant alleles of both genes overpowers each other’s recessive alleles
Redundancy modified phenotypic ratio
15:1
What explains redundancy?
Parallel function of genes on pathway - overlapping roles for two genes which independently make up for absence of function of other
What is a pseudoallele?
Duplicate genes, interact with each other’s alleles
What is epistasis?
Alleles of one locus are suppresses by alleles of a different locus in a given phenotype
What are the types of epistasis?
Recessive epistasis and dominant epistasis
What is recessive epistasis?
When recessive allele of one gene masks effect of either allele of second gene
What is dominant epistasis?
When dominant allele of one gene masks effect of either allele of second gene
Recessive epistasis modified phenotypic ratio
9:3:4
What is a model for recessive epistasis?
Genes in pathway where accumulation of intermediate products are associated with alternative phenotypes
Dominant epistasis modified phenotypic ratio
12:3:1
What is a model for dominant epistasis?
Negative regulators of enzymatic activity, gene is chemical determiner
What is pseudodominance?
The sudden appearance of a recessive phenotype in a pedigree, due to the deletion of a masking dominant gene
