Topic 3 Flashcards
Compare intra-allelic effect and interallelic effect.
Intra-allelic: the effect of different alleles on the protein produced
Interallelic: how different proteins interact
Define haplosufficient.
genes that require only one copy to affect the phenotype (dominant)
Mutations of haplosufficient genes are often dominant/recessive?
recessive
Define haploinsufficiency.
Genes that require more than 1 copy to affect the phenotype (recessive)
Mutations of haploinsufficient genes are often….
dominant
What is pseudodominance?
If chromosome/gene deletion involves haplosufficient genes, any homologous haploinsufficient genes will have a phenotypic effect.
Pseudodominance is when recessive alleles uncovered by deletion will appear dominant in the pedigree
The dosage of alleles in one locus determines the phenotypic coat colour in mice. The yellow coat mutant allele (A^y) is dominant and the brown coat wild type (A+)is recessive. AyA+ causes yellow coats and A+A+ causes gray-brown, but AyAy is embryonic lethal. Why?
The agouti gene (A) codes to a signal peptide important for fur colour AND lipid metabolism.
What is an allelic series?
An allelic series describes the dominance hierarchy of multiple alleles.
A null allele is nonfunctional and a hypomorphic allele has partial function.
Define incomplete dominance.
- Appearance of a third phenotype that ‘blends’ two parental ones
- no clear dominance in the heterozygote
- new phenotype not present in parents
Define codominance.
- More than one allele is dominant
- Heterozygote displays both parental phenotypes
- veriegation
What is pleiotropy?
one allele that affects two or more phenotypes
What is variable (incomplete) penetrance?
Individuals with the same genotype may or may not express the phenotype
Determined by:
- modifier genes
- environmental factors
- allelic variation (similar to non identical alleles)
- complex interaction of the above
What is variable expressivity?
The degree or intensity with which a genotype is expressed (100% of individuals show the consequences of the mutation at the phenotypic level, but there are many possible degrees of ‘severity’)
Ex) Marfan Syndrome tall, long limbs, long fingers
Compare variable penetrance, variable expressivity, and both.
Variable penetrance: all or nothing
Variable expressivity: all or some
Variable penetrance and expressivity: all, some, or none
Compare Polygenic inheritance and monogenic.
Polygenic: many genes (and alleles), affecting the same phenotype
Monogenic: a trait is only affected by 1 gene
Compare polygenic and pleiotropic traits.
Polygenic: many genes contribute to a single effect
Pleiotropic: a gene has multiple effects
What are the five ways alleles at different loci interact with one another?
(1) Additive gene action
(2) Complementary gene action
(3) duplicate gene action
(4) dominant epistasis
(5) recessive epistasis
What is additive gene action?
When the alleles of two genes generate 4 phenotypes in a single trait. Aka a dihybrid cross that only have one trait
Ex) corn snake colour, lentil colour
What is complementary gene action?
2 loci, 1 trait, and 2 phenotypes
Ex) blue bells
What us redundancy (Duplicate gene action)?
2 loci, 1 trait, 2 phenotypes
Dominant alleles of both genes ‘overpower’ each other’s recessive alleles
To have the mutant phenotype, both loci must be homozygous recessive (1/16)
The dominant alleles of both genes alone produce the same phenotypic effect
What is the modified phenotypic ratio for redundancy?
15:1
What is epistasis?
When the alleles of one locus are suppressed by alleles of a different locus in a given phenotype.
A mutant allele of one gene overrides the phenotypic effect of a mutant allele of another gene when both are present in the same genotype
Compare epistasis and dominance.
