5: Gene Interactions
Students determine how multiple genes interact to produce phenotypes, including epistasis in metabolic and biochemical pathways.
LibreTexts reference: Chapter 5: Allele and Gene Interactions 
Matching Inheritance Patterns to Definitions
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Match each of the following inheritance patterns with their corresponding definitions.
Note: Each choice will be used exactly once.
| Your Choice | Prompt | |
|---|---|---|
| 1. epistasis | ||
| 2. incomplete dominance | ||
| 3. codominance | ||
| 4. complete dominance |
Drag one of the choices below:
- A. one gene suppresses the effect of another gene that is NOT its allele
- B. one allele masks the effect of another allele
- C. heterozygote appearance is a blended phenotype of both homozygous phenotypes
- D. heterozygotes equally express both alleles in the phenotype
Inheritance Patterns from Allele-Expression Descriptions
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Which one of the following inheritance patterns correspond to the definition 'one gene suppresses the effect of another gene that is NOT its allele'.
Bacterial Nutrient Requirements in Mutant Metabolic Pathways (5 Metabolites)
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| enzyme 1 | enzyme 2 | enzyme 3 | enzyme 4 | |||||
| B | ⟶ | C | ⟶ | D | ⟶ | F | ⟶ | R |
Look at the metabolic pathway in the table above.
Metabolite R is needed for the bacteria to grow.
Consider a bacterial strain that is mutant for the gene coding for enzyme 2
Which nutrients, when added to minimal media, will help this bacteria grow?
Multiple answers may be correct.
ABO Blood Group Inheritance Patterns
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For the ABO blood group in humans, the iA and iB alleles are codominant and the i allele is recessive.
A father ♂ with blood type B has a daughter ♀ with blood type AB.
Which of the following blood types could the mother ♀ possibly have? Check all that apply.
ABO Blood Group Inheritance in Offspring
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For the ABO blood group in humans, the iA and iB alleles are codominant and the i allele is recessive.
If a female ♀ with type AB blood marries a male ♂ with type A blood, which of the following blood types could their children possibly have? Check all that apply.
Gene Interaction Types in Dihybrid Crosses
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Above are the phenotypic results from a dihybrid cross and double heterozygote test cross. The phenotypes were nine to three to three to one (9:3:3:1).
What type of gene interaction is being shown?
Epistasis in Metabolic Pathway Dihybrid Crosses
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| Gene 1 | Gene 2 | |||
| red | ⟶ | red | ⟶ | white |
A two step metabolic pathway determines the pigment color. When gene 1 is dominant, the gene expresses an enzyme that converts the red precursor pigment into a a second molecule with the same red pigment. When gene 2 is dominant, the gene expresses an enzyme that converts the second red pigment molecule from gene 1 into the white pigment. The white pigment forms only when both genes are dominant, if either gene is homozygous recessive, the red pigment will remain.
The diagram and description above explain the interaction of two genes. Determine the dihybird cross phenotypic ratio.
Genetic Linkage and Epistasis in Dihybrid Crosses (Forward, 6 Choices)
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In a standard dihybrid cross involving two independent genes, the expected F2 phenotypic ratio is 9:3:3:1. A test-cross with an F1 individual and a double recessive usually yields a 1:1:1:1 phenotypic ratio if the genes assort independently.
In a specific cross, F2 progeny exhibit a modified dihybrid ratio of 9:6:1 (instead of 9:3:3:1).
What phenotypic ratio would be expected from a test-cross with an individual from the F1 progeny?
Dihybrid Cross Phenotypic Ratios with Epistasis (Inverse, 6 Choices)
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In a standard dihybrid cross involving two independent genes, the expected F2 phenotypic ratio is 9:3:3:1. A test-cross with an F1 individual and a double recessive usually yields a 1:1:1:1 phenotypic ratio if the genes assort independently.
The progeny from the test-cross exhibited a modified ratio of 1:3, different from the expected 1:1:1:1 ratio.
What phenotypic ratio would be expected in the F2 generation if the original dihybrid cross is continued?
Horse Coat Patterns from Genetic Crosses
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In the American Paint Horse, the Overo gene, Ov, produces a white splotch pattern on the coat. The overo phenotype is seen only when a horse has one Ov copy, Ovov. Horses with two Ov copies, OvOv, suffer from overo lethal white syndrome (OLWS) and die soon after birth. These foals are called white overo because they are completely white before they die. Horses with no Ov copies are solid colored, ovov.
| genotype | phenotype |
|---|---|
| Ov Ov | white overo |
| Ov ov | overo |
| ov ov | solid |
In Appaloosa horse breeds, the Leopard complex gene, Lp, shows incomplete dominance and controls white spotting. One Lp allele, Lplp, produces the leopard phenotype, in which there are spots everywhere. Two Lp alleles, LpLp, produce the fewspot phenotype, in which the horse is mostly white with colored spots.
| genotype | phenotype |
|---|---|
| Lp Lp | fewspot |
| Lp lp | leopard |
| lp lp | solid |
A crossbred horse that is both overo and leopard is called pintaloosa, and these horses are spotted with splotches. A horse that is both overo and fewspot is considered fewspot because the white areas from Lp is indistinguishable from the white from Ov.
| merged phenotypes | leopard gene | |||
|---|---|---|---|---|
| fewspot | leopard | solid | ||
| overo gene | white overo | white | white | white |
| overo | fewspot | pintaloosa | overo | |
| solid | fewspot | leopard | solid | |
Suppose that 16 pairs of pintaloosa horses have one offspring per pair. How many of each phenotype would be expected? Determine the number out of 16 expected for each phenotype. Only count phenotypes for offspring expected to live past one week of age.
How many pintaloosa offspring are expected out of 16?
Metabolic Pathway Precursor Order from Mutant Growth Data (4 Metabolites)
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A mutant screen was carried out to produce the diagram below. The diagram shows different classes (1-4) of mutants for metabolic precursors (W-Z) of a metabolic pathway to produce a product were characterized to either grow (+) or not grow (–) in minimal media.
| W | X | Y | Z | |
| Class 1 | – | + | – | – |
| Class 2 | + | + | + | + |
| Class 3 | – | + | – | + |
| Class 4 | – | + | + | + |
Write the metabolic precursors (W-Z) in their correct order for the pathway without spaces or dashes. For example, XZYW.
Genotype Diversity in Hybrid Crosses (6 Genes, Hint)
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Genotype Diversity in Hybrid Cross
In a hybrid cross, the range of possible genotypes in the offspring is determined by the genetic makeup of the parental organisms.
Assume that all genes sort independently and display complete dominance.
Hint: For each gene pair from the parents, you can get 1, 2, or 3 unique genotypes.
This is based on the combinations: homozygous x homozygous (1), homozygous x heterozygous (2), and heterozygous x heterozygous (3).
Considering the principle of independent assortment, how many unique GENOTYPES could be produced in a hybrid cross between the following individuals?
| Female (♀) | aa Bb Cc DD EE ff |
| Male (♂) | Aa Bb Cc Dd ee FF |
Phenotype Diversity in Genetic Crosses (6 Genes, Hint)
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Phenotype Diversity in Hybrid Cross
In a hybrid cross, you can determine the variety of phenotypes in the offspring by examining the genetic makeup of the parents. Specifically, look at whether each gene can be dominant, recessive, or both.
A dominant gene can mask the effect of its recessive counterpart, thus influencing the number of unique phenotypes.
Hint: To find the number of unique phenotypes, consider each gene pair.
For gene pairs with at least one heterozygous and one either heterozygous or homozygous recessive gene, 2 phenotypes are possible.
For all other combinations, only 1 phenotype is possible.
Assume complete dominance and the principle of independent assortment for all genes.
Given these principles, how many unique PHENOTYPES could result from a hybrid cross between the following individuals?
| Male (♂) | Aa bb Cc Dd Ee ff |
| Female (♀) | AA bb cc Dd EE ff |
Gamete Diversity Through Independent Assortment (7 Genes, Hint)
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Gamete Diversity in Sexual Reproduction
In sexual reproduction, the potential diversity of gametes – such as sperm and eggs in animals, or pollen and ovules in plants – can be calculated based on the genotype of an individual.
How many unique GAMETES could be produced through the process of independent assortment by an individual with the following genotype?
Hint: Remember, each heterozygous gene pair (like `Aa` or `Bb`) can give rise to two (2) different gametes, while homozygous pairs (like `AA`, `BB`, and `aa`, `bb`) can only give rise to one gamete.
Genotype: AA Bb Cc dd Ee Ff gg