1. In a dihybrid cross between two heterozygous individuals (AaBb x AaBb), the expected phenotypic ratio in the F2 generation is:
a) 9:3:3:1
b) 1:2:1
c) 3:1
d) 1:1:1:1
Answer: a) 9:3:3:1
Explanation: The dihybrid cross between two heterozygous individuals (AaBb x AaBb) typically produces a 9:3:3:1 phenotypic ratio in the F2 generation, where 9 represent the dominant traits, and 3 each represent the combinations of recessive and dominant traits.
2. The phenomenon where one gene masks the expression of another gene is called:
a) Epistasis
b) Codominance
c) Incomplete dominance
d) Pleiotropy
Answer: a) Epistasis
Explanation: Epistasis occurs when one gene masks the expression of another gene. This interaction can influence the phenotype in various ways, such as dominant epistasis or recessive epistasis.
3. In a test cross between an individual with genotype AaBb and an individual with genotype aabb, the offspring phenotype ratio would be:
a) 1:1:1:1
b) 1:1
c) 9:3:3:1
d) 1:2:1
Answer: a) 1:1:1:1
Explanation: A test cross between AaBb (heterozygous for both traits) and aabb (homozygous recessive for both traits) produces offspring in a 1:1:1:1 ratio, where each possible combination of alleles occurs equally.
4. Which of the following statements regarding X-linked inheritance is true?
a) X-linked traits are inherited only through the maternal line
b) Males have only one copy of the X chromosome, so they express X-linked recessive traits more often than females
c) Females will always express an X-linked recessive trait if one of their X chromosomes carries the allele
d) X-linked traits cannot be passed from father to son
Answer: b) Males have only one copy of the X chromosome, so they express X-linked recessive traits more often than females
Explanation: Males inherit only one X chromosome (from their mother), so they are more likely to express X-linked recessive traits. Females have two X chromosomes, and the presence of one dominant allele can mask the effect of a recessive allele on the other X chromosome.
5. In a case of incomplete dominance, the F1 generation of a cross between a red-flowered plant (RR) and a white-flowered plant (WW) would produce offspring with what phenotype?
a) 100% red flowers
b) 100% white flowers
c) 100% pink flowers
d) 1:2:1 red, pink, white flowers
Answer: c) 100% pink flowers
Explanation: In incomplete dominance, the heterozygous phenotype is an intermediate between the two homozygous phenotypes. In this case, crossing a red-flowered plant (RR) with a white-flowered plant (WW) would produce offspring with pink flowers (RW).
6. The phenomenon in which a single gene influences multiple traits is called:
a) Pleiotropy
b) Codominance
c) Polygenic inheritance
d) Gene linkage
Answer: a) Pleiotropy
Explanation: Pleiotropy occurs when a single gene affects multiple, seemingly unrelated traits. For example, mutations in the gene responsible for sickle cell anemia also affect the shape of red blood cells and resistance to malaria.
7. Which of the following best describes the concept of “genetic recombination” in eukaryotes?
a) The random distribution of alleles during meiosis
b) The process by which a dominant allele is expressed over a recessive allele
c) The exchange of genetic material between homologous chromosomes during meiosis
d) The independent assortment of chromosomes during mitosis
Answer: c) The exchange of genetic material between homologous chromosomes during meiosis
Explanation: Genetic recombination occurs during meiosis when homologous chromosomes exchange portions of their chromatids in a process called crossing over. This leads to new combinations of alleles in the offspring.
8. The Hardy-Weinberg equilibrium principle assumes all of the following EXCEPT:
a) No mutation occurs
b) No natural selection occurs
c) The population is infinitely large
d) All individuals must have the same genotype
Answer: d) All individuals must have the same genotype
Explanation: Hardy-Weinberg equilibrium assumes random mating, no mutation, no natural selection, and an infinitely large population, but it does not require that all individuals have the same genotype. Genetic variation is maintained in the population under these conditions.
9. Which of the following is an example of a genetic disorder caused by a trinucleotide repeat expansion?
a) Cystic fibrosis
b) Huntington’s disease
c) Sickle cell anemia
d) Down syndrome
Answer: b) Huntington’s disease
Explanation: Huntington’s disease is caused by a trinucleotide repeat expansion (CAG) in the HTT gene. The number of repeats increases with each generation, leading to an earlier onset of symptoms in subsequent generations.
10. Which of the following represents a situation where two different genes are located on the same chromosome and tend to be inherited together?
a) Independent assortment
b) Gene linkage
c) Crossing over
d) Epistasis
Answer: b) Gene linkage
Explanation: Gene linkage occurs when two genes are located close together on the same chromosome, causing them to be inherited together more frequently than genes located on different chromosomes.
11. What is the expected phenotypic ratio in a monohybrid cross between two heterozygous individuals (Aa x Aa) for a dominant-recessive trait?
a) 3:1
b) 1:1
c) 1:2:1
d) 9:3:3:1
Answer: a) 3:1
Explanation: In a monohybrid cross between two heterozygous individuals (Aa x Aa), the offspring will show a 3:1 phenotypic ratio, with 3 individuals showing the dominant phenotype and 1 showing the recessive phenotype.
12. In a pedigree analysis, the presence of a disease in every generation suggests that the disease is likely:
a) X-linked recessive
b) Autosomal dominant
c) X-linked dominant
d) Autosomal recessive
Answer: b) Autosomal dominant
Explanation: Autosomal dominant diseases typically appear in every generation because only one copy of the dominant allele is required for expression. If a disease appears in every generation, it is likely autosomal dominant.
13. In the case of codominance, what would be the expected phenotype of an F1 offspring from a cross between a red-flowered plant (RR) and a white-flowered plant (WW)?
a) Pink flowers
b) Red flowers
c) White flowers
d) Red and white striped flowers
Answer: d) Red and white striped flowers
Explanation: In codominance, both alleles are fully expressed in the heterozygous individual. The F1 offspring of a red-flowered plant (RR) and a white-flowered plant (WW) would show both red and white traits, such as red and white striped flowers.
14. Which of the following is true about the process of crossing over during meiosis?
a) It occurs during metaphase I
b) It results in the formation of recombinant chromosomes
c) It only occurs in female gametes
d) It ensures the production of identical gametes
Answer: b) It results in the formation of recombinant chromosomes
Explanation: Crossing over occurs during prophase I of meiosis and results in the exchange of genetic material between homologous chromosomes, creating recombinant chromosomes and contributing to genetic diversity.
15. A plant with genotype AaBbCc is crossed with another plant of the same genotype. The number of different gametes produced by each parent will be:
a) 2
b) 4
c) 8
d) 16
Answer: c) 8
Explanation: The number of different gametes produced by a parent with genotype AaBbCc can be determined by calculating 2n2^n, where nn is the number of heterozygous loci. In this case, n=3n = 3, so the number of different gametes is 23=82^3 = 8.