Topic 3

Question 1

Compare intra-allelic effect and interallelic effect.

Answer 1

Intra-allelic: the effect of different alleles on the protein produced
Interallelic: how different proteins interact

Question 2

Define haplosufficient.

Answer 2

genes that require only one copy to affect the phenotype (dominant)

Question 3

Mutations of haplosufficient genes are often dominant/recessive?

Answer 3

recessive

Question 4

Define haploinsufficiency.

Answer 4

Genes that require more than 1 copy to affect the phenotype (recessive)

Question 5

Mutations of haploinsufficient genes are often….

Answer 5

dominant

Question 6

What is pseudodominance?

Answer 6

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

Question 7

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?

Answer 7

The agouti gene (A) codes to a signal peptide important for fur colour AND lipid metabolism.

Question 8

What is an allelic series?

Answer 8

An allelic series describes the dominance hierarchy of multiple alleles.
A null allele is nonfunctional and a hypomorphic allele has partial function.

Question 9

Define incomplete dominance.

Answer 9

• Appearance of a third phenotype that ‘blends’ two parental ones
• no clear dominance in the heterozygote
• new phenotype not present in parents

Question 10

Define codominance.

Answer 10

• More than one allele is dominant
• Heterozygote displays both parental phenotypes
  
  • veriegation

Question 11

What is pleiotropy?

Answer 11

one allele that affects two or more phenotypes

Question 12

What is variable (incomplete) penetrance?

Answer 12

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

Question 13

What is variable expressivity?

Answer 13

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

Question 14

Compare variable penetrance, variable expressivity, and both.

Answer 14

Variable penetrance: all or nothing
Variable expressivity: all or some
Variable penetrance and expressivity: all, some, or none

Question 15

Compare Polygenic inheritance and monogenic.

Answer 15

Polygenic: many genes (and alleles), affecting the same phenotype
Monogenic: a trait is only affected by 1 gene

Question 16

Compare polygenic and pleiotropic traits.

Answer 16

Polygenic: many genes contribute to a single effect
Pleiotropic: a gene has multiple effects

Question 17

What are the five ways alleles at different loci interact with one another?

Answer 17

(1) Additive gene action
(2) Complementary gene action
(3) duplicate gene action
(4) dominant epistasis
(5) recessive epistasis

Question 18

What is additive gene action?

Answer 18

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

Question 19

What is complementary gene action?

Answer 19

2 loci, 1 trait, and 2 phenotypes
Ex) blue bells

Question 20

What us redundancy (Duplicate gene action)?

Answer 20

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

Question 21

What is the modified phenotypic ratio for redundancy?

Answer 21

15:1

Question 22

What is epistasis?

Answer 22

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

Question 23

Compare epistasis and dominance.