BIO 413 GENETICS AND GENOMICS
MIDTERM EXAM
Mendelian Principles Molecular Inheritance Mapping Chromosomal
Abnormalities Population Genetics Questions and Answers Verified
Solutions 2026 2027
1. What expected phenotypic ratio results from a dihybrid cross between two individuals
heterozygous for two unlinked, completely dominant genes (AaBb × AaBb)?
A. 1:2:1
B. 3:1
C. 9:3:3:1
D. 1:1:1:1
Rationale: According to Mendel's Law of Independent Assortment, two heterozygous genes sorting
independently produce 9 double dominant, 3 single dominant/recessive, 3 single recessive/dominant, and
1 double recessive phenotypic classes.
2. Which Mendelian principle states that allele pairs separate independently of each other
during gamete formation?
A. Principle of Dominance
B. Principle of Segregation
C. Principle of Independent Assortment
D. Principle of Linkage
Rationale: The Law of Independent Assortment describes how different genes independently separate
from one another when reproductive cells develop during meiosis.
3. What term describes a genetic scenario where a single gene influences multiple
seemingly unrelated phenotypic traits?
A. Epistasis
B. Pleiotropy
C. Incomplete dominance
D. Codominance
, Rationale: Pleiotropy occurs when one gene affects two or more distinct phenotypic characteristics, such
as sickle cell trait causing systemic organ effects.
4. In human ABO blood groups, which inheritance pattern explains why an individual
carrying both A and B alleles expresses both A and B surface antigens simultaneously?
A. Incomplete dominance
B. Codominance
C. Recessive epistasis
D. Polygenic inheritance
Rationale: Codominance occurs when both alleles in a heterozygote are fully and distinctly expressed in
the phenotype without blending.
5. What phenotypic ratio is characteristic of recessive epistasis in a dihybrid cross (e.g.,
Labrador retriever coat color)?
A. 9:3:3:1
B. 9:3:4
C. 12:3:1
D. 15:1
Rationale: Recessive epistasis occurs when homozygous recessive alleles at one locus mask the
phenotypic expression of alleles at a second locus, turning 9:3:3:1 into 9:3:4.
6. During which phase of meiosis does crossing over (homologous recombination)
occur?
A. Prophase I (Pachytene)
B. Metaphase I
C. Anaphase I
D. Prophase II
Rationale: Synapsis and physical exchange of genetic material between non-sister chromatids of
homologous chromosomes take place during the pachytene substage of Prophase I.
7. What map distance unit corresponds to a 1% recombination frequency between two
linked genes?
MIDTERM EXAM
Mendelian Principles Molecular Inheritance Mapping Chromosomal
Abnormalities Population Genetics Questions and Answers Verified
Solutions 2026 2027
1. What expected phenotypic ratio results from a dihybrid cross between two individuals
heterozygous for two unlinked, completely dominant genes (AaBb × AaBb)?
A. 1:2:1
B. 3:1
C. 9:3:3:1
D. 1:1:1:1
Rationale: According to Mendel's Law of Independent Assortment, two heterozygous genes sorting
independently produce 9 double dominant, 3 single dominant/recessive, 3 single recessive/dominant, and
1 double recessive phenotypic classes.
2. Which Mendelian principle states that allele pairs separate independently of each other
during gamete formation?
A. Principle of Dominance
B. Principle of Segregation
C. Principle of Independent Assortment
D. Principle of Linkage
Rationale: The Law of Independent Assortment describes how different genes independently separate
from one another when reproductive cells develop during meiosis.
3. What term describes a genetic scenario where a single gene influences multiple
seemingly unrelated phenotypic traits?
A. Epistasis
B. Pleiotropy
C. Incomplete dominance
D. Codominance
, Rationale: Pleiotropy occurs when one gene affects two or more distinct phenotypic characteristics, such
as sickle cell trait causing systemic organ effects.
4. In human ABO blood groups, which inheritance pattern explains why an individual
carrying both A and B alleles expresses both A and B surface antigens simultaneously?
A. Incomplete dominance
B. Codominance
C. Recessive epistasis
D. Polygenic inheritance
Rationale: Codominance occurs when both alleles in a heterozygote are fully and distinctly expressed in
the phenotype without blending.
5. What phenotypic ratio is characteristic of recessive epistasis in a dihybrid cross (e.g.,
Labrador retriever coat color)?
A. 9:3:3:1
B. 9:3:4
C. 12:3:1
D. 15:1
Rationale: Recessive epistasis occurs when homozygous recessive alleles at one locus mask the
phenotypic expression of alleles at a second locus, turning 9:3:3:1 into 9:3:4.
6. During which phase of meiosis does crossing over (homologous recombination)
occur?
A. Prophase I (Pachytene)
B. Metaphase I
C. Anaphase I
D. Prophase II
Rationale: Synapsis and physical exchange of genetic material between non-sister chromatids of
homologous chromosomes take place during the pachytene substage of Prophase I.
7. What map distance unit corresponds to a 1% recombination frequency between two
linked genes?
