Human ABO blood type is determined by three alleles, two of which (I^A and I^B) produce gene products that modify the H antigen produced by protein activity of an independently assorting H gene. A rare abnormality known as the 'Bombay phenotype' is the result of epistatic interaction between the gene for the ABO blood group and the H gene. Individuals with the Bombay phenotype appear to have blood type O based on the inability of both anti-A antibody and anti-B antibody to detect an antigen. The apparent blood type O in Bombay phenotype is due to the absence of H antigen as a result of homozygous recessive mutations of the H gene. Individuals with the Bombay phenotype have the hh genotype. Use the information above to make predictions about the outcome of the cross shown below.

IᴬIᴮHh×IᴬIᴮHh

The crosses shown are performed between morning glories whose flower color is determined as described in Problem 24. Use the segregation data to determine the genotype of each parental plant.

Two pure-breeding strains of summer squash producing yellow fruit, Y₁ and Y₂, are each crossed to a pure-breeding strain of summer squash producing green fruit, G₁, and to one another. The following results are obtained:

Examine the results of each cross and predict how many genes are responsible for fruit-color determination in summer squash. Justify your answer. 

Two pure-breeding strains of summer squash producing yellow fruit, Y₁ and Y₂, are each crossed to a pure-breeding strain of summer squash producing green fruit, G₁, and to one another. The following results are obtained:

Using clearly defined symbols of your choice, give the genotypes of parental, F₁, and F₂  plants in each cross. 

Two pure-breeding strains of summer squash producing yellow fruit, Y₁ and Y₂, are each crossed to a pure-breeding strain of summer squash producing green fruit, G₁, and to one another. The following results are obtained:

If the F₁ of Crosses I and II are mated, predict the phenotype ratio of the progeny. 

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

Give two examples of modified F₂ ratios produced by epistatic gene interactions and describe how gene interaction results in the ratios.

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

What genetic principle is the basis of this expected F₂ ratio?

Epistatic gene interaction results in a modification of the F₂ dihybrid ratio.

What is the expected F₂ ratio?

When performing a complementation test, how do you know if two mutations complement?