1. Which of the following is the most likely outcome of a cross between two heterozygous plants for a single gene (Aa × Aa)?
a) 100% dominant phenotype
b) 25% recessive phenotype, 75% dominant phenotype
c) 50% dominant phenotype, 50% recessive phenotype
d) 75% dominant phenotype, 25% recessive phenotype
Answer: d) 75% dominant phenotype, 25% recessive phenotype
Explanation: According to Mendelian inheritance, a cross between two heterozygous (Aa) plants results in a genotype ratio of 1 AA : 2 Aa : 1 aa, leading to a 75% dominant phenotype and 25% recessive phenotype.
2. Which of the following techniques is used to introduce a specific gene into a plant genome?
a) Hybridization
b) Polyploidy induction
c) Genetic transformation
d) Backcrossing
Answer: c) Genetic transformation
Explanation: Genetic transformation involves introducing a specific gene or genes into a plant’s genome, often using techniques like Agrobacterium-mediated transformation or particle bombardment.
3. What is the primary goal of backcrossing in plant breeding?
a) To increase the genetic diversity of a population
b) To introduce a specific trait from one variety into another while maintaining the original genotype
c) To generate F1 hybrids for commercial production
d) To produce genetically uniform offspring
Answer: b) To introduce a specific trait from one variety into another while maintaining the original genotype
Explanation: Backcrossing involves crossing a hybrid (F1) back with one of its parental lines to introduce a desirable trait, such as disease resistance, while maintaining the original plant’s genetic background.
4. What does “self-incompatibility” in plants refer to?
a) The ability of plants to self-pollinate effectively
b) The inability of plants to produce pollen
c) The mechanism that prevents self-fertilization to promote genetic diversity
d) The ability of plants to produce offspring without pollination
Answer: c) The mechanism that prevents self-fertilization to promote genetic diversity
Explanation: Self-incompatibility is a genetic mechanism that prevents self-pollination by rejecting the pollen from the same plant, encouraging cross-pollination and promoting genetic diversity.
5. Which of the following statements best describes the concept of “homozygous” in genetics?
a) An individual with two different alleles for a gene
b) An individual with two identical alleles for a gene
c) An individual with no alleles for a gene
d) An individual that expresses a dominant allele
Answer: b) An individual with two identical alleles for a gene
Explanation: A homozygous individual has two identical alleles for a particular gene (either both dominant or both recessive).
6. In polyploidy, what is the primary genetic consequence when a tetraploid (4n) crosses with a diploid (2n)?
a) The offspring will be triploid (3n), which is usually sterile.
b) The offspring will be tetraploid (4n).
c) The offspring will be diploid (2n) and fertile.
d) The offspring will be pentaploid (5n), with high fertility.
Answer: a) The offspring will be triploid (3n), which is usually sterile.
Explanation: When a tetraploid (4n) crosses with a diploid (2n), the resulting offspring will be triploid (3n), which typically exhibits sterility due to irregular chromosome pairing during meiosis.
7. What is the purpose of “marker-assisted selection” (MAS) in plant breeding?
a) To identify plants that carry desirable traits using molecular markers
b) To increase genetic diversity through controlled hybridization
c) To induce genetic mutations that promote beneficial traits
d) To ensure that only homozygous plants are selected for breeding
Answer: a) To identify plants that carry desirable traits using molecular markers
Explanation: Marker-assisted selection (MAS) uses molecular markers linked to specific genes or traits to identify plants carrying those desirable traits, speeding up the breeding process.
8. Which of the following is a key characteristic of quantitative traits in plant genetics?
a) They are controlled by a single gene and exhibit Mendelian inheritance patterns.
b) They are controlled by multiple genes and show continuous variation.
c) They can be easily influenced by environmental factors, but not by genetic factors.
d) They are always recessive and express only in homozygous conditions.
Answer: b) They are controlled by multiple genes and show continuous variation.
Explanation: Quantitative traits are influenced by multiple genes and environmental factors, resulting in a range of phenotypic expressions, often showing continuous variation (e.g., plant height, yield).
9. What is “genomic selection” in plant breeding?
a) The selection of plants based on their phenotype alone
b) The selection of plants based on genomic data to predict breeding values
c) The process of selecting plants for hybridization
d) The selection of plants based on visual markers or traits
Answer: b) The selection of plants based on genomic data to predict breeding values
Explanation: Genomic selection uses genomic data (e.g., DNA markers) to predict the breeding values of plants for complex traits, enhancing breeding efficiency and accuracy.
10. What is the primary goal of “mutation breeding” in plant breeding?
a) To produce hybrids with enhanced vigor and yield potential
b) To create new genetic variation by inducing random mutations
c) To ensure that only homozygous plants are used for breeding
d) To cross two genetically identical plants to maintain uniformity
Answer: b) To create new genetic variation by inducing random mutations
Explanation: Mutation breeding involves using physical or chemical agents to induce mutations in plants, creating new genetic variation that can be used to develop plants with improved traits.
11. In a Mendelian dihybrid cross (AaBb × AaBb), what is the expected phenotypic ratio in the F2 generation?
a) 9:3:3:1
b) 1:1:1:1
c) 3:1
d) 1:2:1
Answer: a) 9:3:3:1
Explanation: The expected phenotypic ratio for a dihybrid cross between two heterozygous individuals (AaBb × AaBb) is 9:3:3:1, where 9 represent plants showing both dominant traits, 3 show the dominant for one and recessive for the other, and so on.
12. Which of the following breeding methods is most commonly used to create new crop varieties with high disease resistance?
a) Mass selection
b) Backcross breeding
c) Hybridization
d) Pure line selection
Answer: b) Backcross breeding
Explanation: Backcross breeding is frequently used to introgress disease resistance genes from one plant variety into another, ensuring the transfer of specific traits while maintaining the overall genetic background of the original cultivar.
13. What is “inbreeding depression” in plant breeding?
a) The increase in vigor and fertility due to close inbreeding
b) The reduction in genetic diversity due to self-pollination
c) The reduction in plant vigor and fertility due to continued inbreeding
d) The enhancement of desirable traits through inbreeding
Answer: c) The reduction in plant vigor and fertility due to continued inbreeding
Explanation: Inbreeding depression occurs when repeated inbreeding leads to a decrease in plant vigor, fertility, and overall performance due to the expression of harmful recessive alleles.
14. Which of the following methods is best suited for increasing the seed set in apomictic plants (plants that reproduce asexually through seeds)?
a) Cross-pollination
b) Self-pollination
c) Inducing polyploidy
d) Tissue culture
Answer: c) Inducing polyploidy
Explanation: Polyploidy can lead to the production of more viable seeds in apomictic plants by increasing the fertility and seed set, as apomixis bypasses the need for sexual reproduction.
15. Which of the following is an example of “heterosis” (hybrid vigor) in plant breeding?
a) F1 hybrids outperform both parent plants in yield and disease resistance.
b) Crossbreeding leads to genetic uniformity in the progeny.
c) Offspring exhibit a mix of traits from both parent plants but do not show superior performance.
d) The F2 generation is genetically more diverse than the F1 generation.
Answer: a) F1 hybrids outperform both parent plants in yield and disease resistance.
Explanation: Heterosis, or hybrid vigor, occurs when the F1 hybrid exhibits superior traits, such as increased yield, disease resistance, and growth compared to both parental plants.