BIOD 210 GENETICS
Exam MODULE 3 Questions and
Ansẉers
2026\2027 update
1. Q: What is expressivity?
ANSWER The degree to which a specific genotype is expressed
phenotypically in an individual (e.g., mild vs. severe symptoms).
2. Q: What is the difference between penetrance and expressivity?
ANSWER Penetrance is the percentage of individuals with a genotype
who show the phenotype, while expressivity is the degree or
intensity of that phenotypic expression.
3. Q: What is a gene interaction?
ANSWER When two or more different genes influence the outcome of
a single phenotypic trait.
4. Q: What is the phenotypic ratio for a dihybrid cross showing
duplicate recessive epistasis (complementary gene action)?
ANSWER 9:7.
5. Q: What is the phenotypic ratio for duplicate dominant epistasis?
ANSWER 15:1.
, 6. Q: What is the phenotypic ratio for dominant and recessive
epistasis (dominant suppression)?
ANSWER 13:3.
7. Q: What is a sex-influenced trait?
ANSWER A trait where the dominance relationship between alleles
depends on the sex of the individual (e.g., male pattern baldness is
dominant in males, recessive in females).
8. Q: What is a sex-limited trait?
ANSWER A trait that is expressed in only one sex, even though the
gene is present in both sexes (e.g., milk production in females, horn
development in males).
9. Q: Give a classic example of a sex-influenced trait.
ANSWER Male pattern baldness in humans.
10. Q: Give a classic example of a sex-limited trait.
ANSWER Milk production in cattle or egg production in hens.
11. Q: What is a maternal effect?
ANSWER A phenomenon where the phenotype of the offspring is
determined entirely by the genotype of the mother, regardless of
the offspring's own genotype.
12. Q: How do maternal effect genes function mechanistically?
Exam MODULE 3 Questions and
Ansẉers
2026\2027 update
1. Q: What is expressivity?
ANSWER The degree to which a specific genotype is expressed
phenotypically in an individual (e.g., mild vs. severe symptoms).
2. Q: What is the difference between penetrance and expressivity?
ANSWER Penetrance is the percentage of individuals with a genotype
who show the phenotype, while expressivity is the degree or
intensity of that phenotypic expression.
3. Q: What is a gene interaction?
ANSWER When two or more different genes influence the outcome of
a single phenotypic trait.
4. Q: What is the phenotypic ratio for a dihybrid cross showing
duplicate recessive epistasis (complementary gene action)?
ANSWER 9:7.
5. Q: What is the phenotypic ratio for duplicate dominant epistasis?
ANSWER 15:1.
, 6. Q: What is the phenotypic ratio for dominant and recessive
epistasis (dominant suppression)?
ANSWER 13:3.
7. Q: What is a sex-influenced trait?
ANSWER A trait where the dominance relationship between alleles
depends on the sex of the individual (e.g., male pattern baldness is
dominant in males, recessive in females).
8. Q: What is a sex-limited trait?
ANSWER A trait that is expressed in only one sex, even though the
gene is present in both sexes (e.g., milk production in females, horn
development in males).
9. Q: Give a classic example of a sex-influenced trait.
ANSWER Male pattern baldness in humans.
10. Q: Give a classic example of a sex-limited trait.
ANSWER Milk production in cattle or egg production in hens.
11. Q: What is a maternal effect?
ANSWER A phenomenon where the phenotype of the offspring is
determined entirely by the genotype of the mother, regardless of
the offspring's own genotype.
12. Q: How do maternal effect genes function mechanistically?
