BIOL 2500 - Topic 5 (part 7)

4 or more genotypes observed

9:3:3:1 or more —> no genetic interaction or incomplete dominance

3 observed phenotypes

1.) 9:6:1 —> Dominant gene action

2.) 9:3:4 —> Recessive epistasis

3.) 12:3:1 —> Dominant epistasis `

2 observed phenotypes

1.) 9:7 —> Complementary gene action

2.) 15:1 —> Duplicate gene action

3.) 13:3 —> Dominant suppression

9:3:3:1 ratio

No genetic interaction, with complete penetrance

9:7 ratio

Complementary gene interaction

Complementary gene interaction

1.) Two different genes work together in tandem to produce a single gene product

2.) Therefore, the dominant phenotype is only shown when there is at least one dominant allele at each locus

3.) If you only one dominant allele in one of the loci, the recessive phenotype is produced

Double mutants in complementary gene interactions

They have the same phenotype as both of the single-gene mutants

15:1 ratio

Duplicate gene action

Duplicate gene action

1.) It is when two genes duplicate each others activity, either by producing the same protein or they are two different proteins with the same function

2.) Therefore, you only need one dominant allele in either of the two loci to get the dominant phenotype

3.) You only get the recessive phenotype when both of the loci are homozygous recessive

9:6:1 ratio

Dominant gene interaction

Dominant gene interaction

1.) Need at least one dominant allele at both loci to get the dominant phenotype

2.) Need homozygous recessive at both loci to get the recessive phenotype

3.) Having only one dominant at one of the two loci results in a phenotype that is similar to incomplete dominance, such that a blended product is observed

Dominant gene interaction vs. incomplete dominance

1.) Dominant gene interactions are still complete dominance, because the blended product can be either homozygous dominant or heterozygous and it involves two loci

2.) Incomplete dominance requires heterozygotes, and it only involves one locus

Incomplete dominance for two traits

It results in 9 phenotypes rather than three, since there are 2 loci

Epistasis

It is when a genotype at one locus masks the expression of the genotype at another loci

9:3:4

Recessive epistasis

Recessive epistasis

1.) At least one dominant allele at both loci results in the dominant phenotype

2.) Having no dominant allele at one specific loci masks the expression of the other loci, regardless of if it has the dominant allele or not, therefore resulting in the recessive phenotype

Recessive epistasis example

1.) Usually involves colouring such that one locus codes for the pigment, the other is responsible for depositing the pigment

2.) Therefore, if no dominant allele is found in the locus for depositing the pigment, it won’t matter what allele the other locus for the pigment has, as it will lead to no colour

12:3:1 ratio

Dominant epistasis

Dominant epistasis

1.) It is when the presence of a dominant allele at a specific locus masks the expression of the other locus, regardless of the allele that is present on the other locus

2.) The two other phenotypes are only seen when the specific locus is homozygously recessive

Dominant epistasis example

It is usually seen in colourings, such that the presence of the dominant allele at the locus that determines whether or not there will be pigment masks the expression of the locus that produces the pigment

13:3 ratio

Dominant suppression

Dominant suppression

1.) It is when the presence of the dominant allele at one locus suppresses/inhibits (not masks) the expression of the second locus

2.) The only time the other phenotype is presented is when the specific locus is homozygous recessive and the other locus has its dominant allele