PCB 3063 Exam 1 V3 | PCB 3063 Genetics
| Actual Q&A with Rationale (PCB3063
Exam 1) | University of Central Florida
1. Which Mendelian principle states that the two alleles for a trait separate during the
formation of gametes?
A. Law of Independent Assortment
B. Law of Unit Factors
C. Law of Dominance
D. Law of Segregation
Answer: D
Rationale: The Law of Segregation describes the separation of allele pairs during gamete
production, ensuring each gamete carries only one allele. This fundamental principle was
derived from Mendel’s observations of monohybrid crosses. It explains why offspring
inherit one genetic factor from each parent for a specific trait.
2. In a dihybrid cross between two individuals heterozygous for two independently assorting
genes (AaBb x AaBb), what is the expected phenotypic ratio?
A. 3:1
B. 9:3:3:1
C. 1:2:1
,D. 1:1:1:1
Answer: B
Rationale: The 9:3:3:1 ratio is the classic phenotypic result for a dihybrid cross involving
dominant and recessive traits. This ratio assumes that the two genes are located on
different chromosomes and assort independently. It represents the combinations of the
two 3:1 monohybrid ratios multiplied together.
3. Which stage of the cell cycle is characterized by the replication of DNA?
A. G1 phase
B. G2 phase
C. M phase
D. S phase
Answer: D
Rationale: The S phase, or synthesis phase, is the specific period during interphase when
the cell’s DNA is duplicated. This process ensures that each daughter cell will receive a
complete set of genetic information. After S phase, each chromosome consists of two
identical sister chromatids.
4. What is the primary purpose of a testcross in genetics?
A. To determine the genotype of an individual with a dominant phenotype
B. To determine if a trait is sex-linked
, C. To create a true-breeding line
D. To test for environmental effects on gene expression
Answer: A
Rationale: A testcross involves breeding an individual of unknown genotype with a
homozygous recessive individual. If any offspring show the recessive phenotype, the
unknown parent must be heterozygous. This technique is a standard tool for identifying
whether an organism is homozygous dominant or heterozygous.
5. If a cell has 24 chromosomes at the beginning of G1, how many sister chromatids will it
have during G2?
A. 12
B. 48
C. 24
D. 96
Answer: B
Rationale: During the S phase, every one of the 24 chromosomes is replicated to form two
sister chromatids. Therefore, by the time the cell reaches the G2 phase, there are 48 sister
chromatids present. The total number of chromosomes remains 24, but each consists of a
pair of chromatids.
| Actual Q&A with Rationale (PCB3063
Exam 1) | University of Central Florida
1. Which Mendelian principle states that the two alleles for a trait separate during the
formation of gametes?
A. Law of Independent Assortment
B. Law of Unit Factors
C. Law of Dominance
D. Law of Segregation
Answer: D
Rationale: The Law of Segregation describes the separation of allele pairs during gamete
production, ensuring each gamete carries only one allele. This fundamental principle was
derived from Mendel’s observations of monohybrid crosses. It explains why offspring
inherit one genetic factor from each parent for a specific trait.
2. In a dihybrid cross between two individuals heterozygous for two independently assorting
genes (AaBb x AaBb), what is the expected phenotypic ratio?
A. 3:1
B. 9:3:3:1
C. 1:2:1
,D. 1:1:1:1
Answer: B
Rationale: The 9:3:3:1 ratio is the classic phenotypic result for a dihybrid cross involving
dominant and recessive traits. This ratio assumes that the two genes are located on
different chromosomes and assort independently. It represents the combinations of the
two 3:1 monohybrid ratios multiplied together.
3. Which stage of the cell cycle is characterized by the replication of DNA?
A. G1 phase
B. G2 phase
C. M phase
D. S phase
Answer: D
Rationale: The S phase, or synthesis phase, is the specific period during interphase when
the cell’s DNA is duplicated. This process ensures that each daughter cell will receive a
complete set of genetic information. After S phase, each chromosome consists of two
identical sister chromatids.
4. What is the primary purpose of a testcross in genetics?
A. To determine the genotype of an individual with a dominant phenotype
B. To determine if a trait is sex-linked
, C. To create a true-breeding line
D. To test for environmental effects on gene expression
Answer: A
Rationale: A testcross involves breeding an individual of unknown genotype with a
homozygous recessive individual. If any offspring show the recessive phenotype, the
unknown parent must be heterozygous. This technique is a standard tool for identifying
whether an organism is homozygous dominant or heterozygous.
5. If a cell has 24 chromosomes at the beginning of G1, how many sister chromatids will it
have during G2?
A. 12
B. 48
C. 24
D. 96
Answer: B
Rationale: During the S phase, every one of the 24 chromosomes is replicated to form two
sister chromatids. Therefore, by the time the cell reaches the G2 phase, there are 48 sister
chromatids present. The total number of chromosomes remains 24, but each consists of a
pair of chromatids.
