BIOD 210 Genetics Final Exam
Instructions: This exam consists of 120 multiple-choice questions. Select the single best answer
for each question. A detailed rationale is provided for each correct answer.
Section 1: Foundational Concepts and Mendelian Genetics (Questions 1-20)
Question 1: What is the fundamental unit of heredity?
A) Chromosome
B) Gene
C) Nucleotide
D) Phenotype
Answer: B) Gene
Rationale: A gene is a specific sequence of DNA that contains the instructions for a particular
trait or function. Chromosomes are structures that carry genes, nucleotides are the building
blocks of DNA, and a phenotype is the observable expression of a gene.
Question 2: In a diploid organism, how many alleles for a single autosomal gene are present in a
somatic cell?
A) 1
B) 2
C) 4
D) It varies depending on the gene.
Answer: B) 2
Rationale: Diploid organisms have two sets of chromosomes, one from each parent. Therefore,
they possess two copies of each autosomal gene, which can be the same (homozygous) or
different (heterozygous) alleles.
Question 3: Alternative forms of a gene are known as:
A) Loci
B) Chromatids
C) Alleles
D) Centromeres
Answer: C) Alleles
Rationale: Alleles are the different versions of a gene that arise by mutation and are found at
the same locus on homologous chromosomes. A locus is the specific physical location of a gene
on a chromosome.
Question 4: The physical expression of a genotype is referred to as the:
A) Genotype
B) Phenotype
,C) Allele
D) Genome
Answer: B) Phenotype
Rationale: The phenotype is the observable or measurable characteristic of an organism,
resulting from the interaction of its genotype with the environment. The genotype is the genetic
makeup itself.
Question 5: Which of the following represents a heterozygous genotype?
A) AA
B) aa
C) Aa
D) aA
Answer: C) Aa
Rationale: A heterozygous genotype has two different alleles at a specific locus (e.g., A and a).
'AA' and 'aa' are homozygous genotypes. While 'aA' represents the same alleles, the
conventional notation is to write the dominant allele first (Aa).
Question 6: In Mendel's pea plant experiments, the parental (P) generation was true-breeding.
What does true-breeding mean?
A) The plants were heterozygous for the trait in question.
B) The plants were produced from cross-pollination.
C) The plants were homozygous for the trait in question.
D) The plants showed a dominant phenotype.
Answer: C) The plants were homozygous for the trait in question.
Rationale: True-breeding organisms are homozygous for a particular trait, meaning they have
two identical alleles. When self-pollinated, they always produce offspring with the same
phenotype.
Question 7: What is the genotypic ratio of the offspring from a monohybrid cross (Aa x Aa)?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
Answer: C) 1:2:1
Rationale: A cross between two heterozygotes (Aa x Aa) produces offspring with the genotypic
ratio of 1 AA : 2 Aa : 1 aa. The 3:1 ratio is the phenotypic ratio for a cross with complete
dominance.
Question 8: In a monohybrid cross with complete dominance, what is the expected phenotypic
ratio in the F2 generation?
,A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
Answer: B) 3:1
Rationale: With complete dominance, both AA and Aa genotypes express the dominant
phenotype. Therefore, out of four offspring, three will show the dominant phenotype and one
will show the recessive phenotype, resulting in a 3:1 phenotypic ratio.
Question 9: Mendel's law of segregation states that:
A) Genes on different chromosomes assort independently.
B) Alleles of a gene separate from each other during gamete formation.
C) One allele is always dominant over the other.
D) The phenotype is determined by the environment.
Answer: B) Alleles of a gene separate from each other during gamete formation.
Rationale: The Law of Segregation is based on the separation of homologous chromosomes
during meiosis, ensuring each gamete receives only one allele from each gene pair.
Question 10: Mendel's law of independent assortment applies to genes that are:
A) On the same chromosome and close together.
B) On different chromosomes.
C) Always inherited together.
D) Involved in the same metabolic pathway.
Answer: B) On different chromosomes.
Rationale: The Law of Independent Assortment states that alleles of different genes assort
independently of one another during gamete formation. This occurs when genes are located on
different, non-homologous chromosomes. Genes on the same chromosome may not assort
independently due to linkage.
Question 11: A test cross is performed to determine the genotype of an organism with a
dominant phenotype. The organism is crossed with a:
A) Homozygous dominant individual.
B) Heterozygous individual.
C) Homozygous recessive individual.
D) Individual with the same phenotype.
Answer: C) Homozygous recessive individual.
Rationale: A test cross involves crossing an individual with a dominant phenotype (unknown
genotype) with a homozygous recessive individual. The phenotypes of the offspring reveal the
genotype of the unknown parent.
, Question 12: In a test cross, if all offspring show the dominant phenotype, what is the genotype
of the unknown parent?
A) AA
B) Aa
C) aa
D) It cannot be determined.
Answer: A) AA
Rationale: If the unknown parent were AA, all offspring (AA or Aa) would display the dominant
phenotype. If the parent were Aa, approximately half of the offspring would be recessive (aa).
Question 13: A cross between two dihybrid individuals (AaBb x AaBb) is expected to produce a
phenotypic ratio of:
A) 1:1:1:1
B) 3:1
C) 9:3:3:1
D) 1:2:1
Answer: C) 9:3:3:1
Rationale: This is the classic dihybrid phenotypic ratio, assuming independent assortment and
complete dominance for both genes.
Question 14: If an organism has the genotype AaBb, which of the following gametes can it
produce?
A) AB, Ab, aB, ab
B) AA, BB, aa, bb
C) A, a, B, b
D) Aa, Bb
Answer: A) AB, Ab, aB, ab
Rationale: During meiosis, the alleles for different genes assort independently. The organism
can produce gametes with all possible combinations of one allele from each gene.
Question 15: A condition in which a single gene has multiple phenotypic effects is called:
A) Epistasis
B) Pleiotropy
C) Polygenic inheritance
D) Incomplete dominance
Answer: B) Pleiotropy
Rationale: Pleiotropy occurs when one gene influences multiple, seemingly unrelated traits. An
example is the gene for sickle cell anemia, which affects blood cell shape, oxygen capacity, and
resistance to malaria.
Instructions: This exam consists of 120 multiple-choice questions. Select the single best answer
for each question. A detailed rationale is provided for each correct answer.
Section 1: Foundational Concepts and Mendelian Genetics (Questions 1-20)
Question 1: What is the fundamental unit of heredity?
A) Chromosome
B) Gene
C) Nucleotide
D) Phenotype
Answer: B) Gene
Rationale: A gene is a specific sequence of DNA that contains the instructions for a particular
trait or function. Chromosomes are structures that carry genes, nucleotides are the building
blocks of DNA, and a phenotype is the observable expression of a gene.
Question 2: In a diploid organism, how many alleles for a single autosomal gene are present in a
somatic cell?
A) 1
B) 2
C) 4
D) It varies depending on the gene.
Answer: B) 2
Rationale: Diploid organisms have two sets of chromosomes, one from each parent. Therefore,
they possess two copies of each autosomal gene, which can be the same (homozygous) or
different (heterozygous) alleles.
Question 3: Alternative forms of a gene are known as:
A) Loci
B) Chromatids
C) Alleles
D) Centromeres
Answer: C) Alleles
Rationale: Alleles are the different versions of a gene that arise by mutation and are found at
the same locus on homologous chromosomes. A locus is the specific physical location of a gene
on a chromosome.
Question 4: The physical expression of a genotype is referred to as the:
A) Genotype
B) Phenotype
,C) Allele
D) Genome
Answer: B) Phenotype
Rationale: The phenotype is the observable or measurable characteristic of an organism,
resulting from the interaction of its genotype with the environment. The genotype is the genetic
makeup itself.
Question 5: Which of the following represents a heterozygous genotype?
A) AA
B) aa
C) Aa
D) aA
Answer: C) Aa
Rationale: A heterozygous genotype has two different alleles at a specific locus (e.g., A and a).
'AA' and 'aa' are homozygous genotypes. While 'aA' represents the same alleles, the
conventional notation is to write the dominant allele first (Aa).
Question 6: In Mendel's pea plant experiments, the parental (P) generation was true-breeding.
What does true-breeding mean?
A) The plants were heterozygous for the trait in question.
B) The plants were produced from cross-pollination.
C) The plants were homozygous for the trait in question.
D) The plants showed a dominant phenotype.
Answer: C) The plants were homozygous for the trait in question.
Rationale: True-breeding organisms are homozygous for a particular trait, meaning they have
two identical alleles. When self-pollinated, they always produce offspring with the same
phenotype.
Question 7: What is the genotypic ratio of the offspring from a monohybrid cross (Aa x Aa)?
A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
Answer: C) 1:2:1
Rationale: A cross between two heterozygotes (Aa x Aa) produces offspring with the genotypic
ratio of 1 AA : 2 Aa : 1 aa. The 3:1 ratio is the phenotypic ratio for a cross with complete
dominance.
Question 8: In a monohybrid cross with complete dominance, what is the expected phenotypic
ratio in the F2 generation?
,A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1
Answer: B) 3:1
Rationale: With complete dominance, both AA and Aa genotypes express the dominant
phenotype. Therefore, out of four offspring, three will show the dominant phenotype and one
will show the recessive phenotype, resulting in a 3:1 phenotypic ratio.
Question 9: Mendel's law of segregation states that:
A) Genes on different chromosomes assort independently.
B) Alleles of a gene separate from each other during gamete formation.
C) One allele is always dominant over the other.
D) The phenotype is determined by the environment.
Answer: B) Alleles of a gene separate from each other during gamete formation.
Rationale: The Law of Segregation is based on the separation of homologous chromosomes
during meiosis, ensuring each gamete receives only one allele from each gene pair.
Question 10: Mendel's law of independent assortment applies to genes that are:
A) On the same chromosome and close together.
B) On different chromosomes.
C) Always inherited together.
D) Involved in the same metabolic pathway.
Answer: B) On different chromosomes.
Rationale: The Law of Independent Assortment states that alleles of different genes assort
independently of one another during gamete formation. This occurs when genes are located on
different, non-homologous chromosomes. Genes on the same chromosome may not assort
independently due to linkage.
Question 11: A test cross is performed to determine the genotype of an organism with a
dominant phenotype. The organism is crossed with a:
A) Homozygous dominant individual.
B) Heterozygous individual.
C) Homozygous recessive individual.
D) Individual with the same phenotype.
Answer: C) Homozygous recessive individual.
Rationale: A test cross involves crossing an individual with a dominant phenotype (unknown
genotype) with a homozygous recessive individual. The phenotypes of the offspring reveal the
genotype of the unknown parent.
, Question 12: In a test cross, if all offspring show the dominant phenotype, what is the genotype
of the unknown parent?
A) AA
B) Aa
C) aa
D) It cannot be determined.
Answer: A) AA
Rationale: If the unknown parent were AA, all offspring (AA or Aa) would display the dominant
phenotype. If the parent were Aa, approximately half of the offspring would be recessive (aa).
Question 13: A cross between two dihybrid individuals (AaBb x AaBb) is expected to produce a
phenotypic ratio of:
A) 1:1:1:1
B) 3:1
C) 9:3:3:1
D) 1:2:1
Answer: C) 9:3:3:1
Rationale: This is the classic dihybrid phenotypic ratio, assuming independent assortment and
complete dominance for both genes.
Question 14: If an organism has the genotype AaBb, which of the following gametes can it
produce?
A) AB, Ab, aB, ab
B) AA, BB, aa, bb
C) A, a, B, b
D) Aa, Bb
Answer: A) AB, Ab, aB, ab
Rationale: During meiosis, the alleles for different genes assort independently. The organism
can produce gametes with all possible combinations of one allele from each gene.
Question 15: A condition in which a single gene has multiple phenotypic effects is called:
A) Epistasis
B) Pleiotropy
C) Polygenic inheritance
D) Incomplete dominance
Answer: B) Pleiotropy
Rationale: Pleiotropy occurs when one gene influences multiple, seemingly unrelated traits. An
example is the gene for sickle cell anemia, which affects blood cell shape, oxygen capacity, and
resistance to malaria.
