1. Which of the following methods can create a new breed carrying the diploid chromosome set of two species?

• A. Mutation induction by 5BU and acridine.
• Incorrect. 5BU and acridine are gene mutagens, they do not create new breeds carrying diploid chromosome sets of two species.
• B. Wide hybridization followed by polyploidy and protoplast fusion.
• Correct. Wide hybridization produces a hybrid organism carrying chromosomes from two different species. Polyploidy doubles the chromosome set of the hybrid, creating a diploid set. Protoplast fusion removes the cell wall of plants, allowing cells from different species to combine and form hybrid cells.
• C. Wide hybridization followed by polyploidy and gene transfer technique.
• Incorrect. Gene transfer techniques modify one or a few genes in the chromosome set, not the entire diploid set from two species.
• D. Mutation induction by radiation and colchicine.
• Incorrect. Radiation and colchicine induce gene mutations or chromosomal structural changes, not the creation of new breeds carrying diploid chromosome sets of two species.
• Note: Wide hybridization followed by polyploidy is commonly used to create new breeds in plants, as polyploidy is difficult to achieve in animals.

2. A sheep embryo with the genotype AAbb was implanted and developed into 10 individuals. These 10 individuals:

• A. can interbreed to produce offspring.
• Correct. All individuals have the same genotype AAbb, so they can interbreed.
• B. have the same reaction norms.
• Correct. These individuals originated from the same embryo, so they have identical genotypes and therefore similar reaction norms.
• C. can have the same or different genders.
• Incorrect. The implanted embryo will develop into individuals with the same gender, as the gender of the embryo is already determined.
• D. have completely different phenotypes.
• Incorrect. They will have the same phenotype due to their identical genotypes.
• Note: Embryo transfer is an asexual reproduction technique, resulting in individuals with identical genotypes.

3. The pollen grains of a plant with the genotype AabbDdEE are cultured into haploid lines, then doubled to create homozygous diploid lines. What is the maximum number of homozygous lines that can be produced from this plant?

• A. 2 lines
• B. 6 lines
• C. 8 lines
• D. 4 lines
• Correct. The plant with the genotype AabbDdEE can produce 4 types of haploid gametes: AbDE, AbDe, abDE, abDe. Pollen culture will generate 4 corresponding haploid lines. Doubling these haploid lines will create 4 homozygous diploid lines: AABBddee, AAbbDDee, aaBBddee, aabbDDee.
• Note: Pollen culture produces haploid lines, which are then doubled to create homozygous lines. The maximum number of homozygous lines equals the number of haploid gametes the plant can produce.

4. Crossbred offspring exhibit the highest hybrid vigor but are not used for sexual reproduction because:

• A. they carry harmful recessive genes that dominant genes cannot mask.
• Incorrect. Crossbred offspring typically carry dominant genes that mask harmful recessive genes.
• B. offspring have a reduced heterozygosity, leading to the appearance of harmful recessive homozygotes.
• Correct. Crossbred offspring are heterozygous, and self-fertilization or inbreeding reduces heterozygosity, increasing the likelihood of harmful recessive homozygotes, causing inbreeding depression.
• C. they exhibit some undesirable traits from either parent.
• Incorrect. Crossbred offspring generally express desirable traits from both parents, leading to hybrid vigor.
• D. the cost is very high, making them economically inefficient for breeding.
• Incorrect. Hybrid vigor is economically beneficial, reducing production costs.
• Note: Hybrid vigor is the phenomenon where F1 offspring exhibit increased vigor, growth, yield, and resilience compared to their parents. This vigor tends to decline in subsequent generations.

5. The following steps are involved in plant cell protoplast fusion:

• (1). Protoplasts from two species are placed in a special medium to fuse together.
• (2). The hybrid cells are introduced into a special culture medium for division and regeneration into interspecific hybrid plants.
• (3). The cellulose wall of the cells is removed.

The correct order of the steps is:

• A. (1) -> (2) -> (3)
• B. (3) -> (2) -> (1)
• C. (2) -> (1) -> (3)
• D. (3) -> (1) -> (2)
• Correct. Before protoplast fusion, the cellulose cell wall must be removed to create protoplasts. After fusion, the hybrid cells are cultured in a specific medium to divide and regenerate into hybrid plants.
• Note: Protoplast fusion is a technique for creating new breeds by fusing protoplasts (cells without cell walls) from two different species.

6. Which of the following methods can be used to create multiple new plant varieties from a single initial variety, all homozygous for all gene pairs?

• A. Pollen culture
• Correct. Pollen culture generates haploid lines, which are then doubled to create homozygous lines.
• B. Protoplast fusion
• Incorrect. Protoplast fusion produces hybrid cells, not necessarily homozygous lines.
• C. Continuous self-fertilization for many generations
• Incorrect. Continuous self-fertilization increases homozygosity but doesn’t guarantee homozygosity for all genes.
• D. Selection of somaclonal variant cell lines
• Incorrect. Selection of somaclonal variant cell lines can create new varieties but not necessarily homozygous for all genes.
• Note: Pollen culture is an efficient method for generating homozygous varieties.

7. In cross-pollinated varieties, continuous self-fertilization and inbreeding over many generations leads to inbreeding depression. This is because self-fertilization and inbreeding cause:

• A. increased homozygosity, decreased heterozygosity, and the appearance of harmful recessive genes.
• Incorrect. Homozygosity increases and heterozygosity decreases, but harmful recessive genes may not always appear.
• B. decreased heterozygosity, increased homozygosity, and the appearance of harmful recessive genes.
• Incorrect. Heterozygosity decreases, homozygosity increases, but harmful recessive genes may not always appear.
• C. decreased heterozygosity, increased homozygosity, and the appearance of harmful recessive homozygotes.
• Correct. Self-fertilization and inbreeding decrease heterozygosity and increase homozygosity, leading to the expression of harmful recessive genes in homozygous form, causing inbreeding depression.
• D. the appearance of harmful recessive gene mutations in the breeding population.
• Incorrect. Self-fertilization and inbreeding do not increase the rate of recessive gene mutations.
• Note: Inbreeding depression is a decline in vigor, yield, and resilience in plant or animal varieties due to the expression of harmful recessive genes.

8. Artificial mutation induction is particularly effective for:

• A. unicellular organisms that reproduce asexually.
• Correct. Unicellular organisms reproducing asexually rapidly produce numerous individuals carrying mutations.
• B. all organisms in the biosphere.
• Incorrect. Artificial mutation induction isn’t effective for all organisms.
• C. lower animals and higher plants.
• Incorrect. Artificial mutation induction isn’t effective for all lower animals and higher plants.
• D. higher animals and flowering plants.
• Incorrect. Artificial mutation induction isn’t effective for all higher animals and flowering plants.
• Note: Artificial mutation induction uses mutagens (radiation, chemicals) to induce mutations in organisms. This method is efficient for unicellular organisms that reproduce asexually.

9. Suppose there are two plants from different species with genotypes AaBB and DDEe. These plants are used for cell culture technology to create offspring. According to theory, which of the following statements about these offspring are correct?

• (1). Offspring produced by cultivating somatic cells of each plant will have genotypes AaBB or DDEe.
• Correct. Somatic cell culture produces offspring with the same genotype as the parent cell.
• (2). Cultivating pollen grains separately from each plant and then doubling them will result in 8 homozygous lines with different genotypes.
• Incorrect. Plant AaBB will produce 2 haploid gametes: AB, aB. Plant DDEe will produce 2 haploid gametes: DE, De. Cultivating pollen grains from these plants will produce a maximum of 4 homozygous lines: AABB, aaBB, DDEE, DDee.
• (3). Offspring produced by cultivating pollen grains of each plant and inducing diploidy will have genotypes AABB, aaBB, or DDEE, DDee.
• Correct. Cultivating pollen grains and inducing diploidy produces homozygous lines from haploid gametes.
• (4). Offspring produced by somatic cell hybridization (protoplast fusion) of the two plants will have the genotype AaBBDDEe.
• Correct. Protoplast fusion creates hybrid cells with the combined chromosomes from both parent cells.
• Note: Pollen culture produces haploid lines, which are then doubled to create homozygous lines. Protoplast fusion produces hybrid plants with combined chromosomes from both species.

10. Consider the following statements:

• (1). Heterosis is expressed in the first generation and remains stable in subsequent generations.
• Incorrect. Heterosis typically declines in subsequent generations.
• (2). When crossing different lines or species, the hybrid offspring always exhibit heterosis.
• Incorrect. Not all crosses between different lines or species result in heterosis.
• (3). If hybrid offspring are used as breeding stock, inbreeding depression will occur because the offspring are heterozygous.
• Correct. Hybrid offspring are heterozygous, and self-fertilization or inbreeding reduces heterozygosity, leading to inbreeding depression.
• (4). In the same cross combination, the reciprocal cross may not show heterosis, but the original cross may show heterosis, and vice versa.
• Correct. Reciprocal crosses can sometimes produce different levels of heterosis.
• (5). In pure lines, self-fertilization does not cause inbreeding depression.
• Correct. Pure lines are homozygous, and self-fertilization doesn’t alter their genotypes, so no inbreeding depression occurs.
• (6). In animal breeds, inbreeding always causes inbreeding depression.
• Incorrect. Inbreeding doesn’t always cause inbreeding depression.
• Note: Heterosis is generally expressed in the F1 generation and declines in subsequent generations. Hybrid offspring, being heterozygous, are susceptible to inbreeding depression if they are self-fertilized or inbred.

11. Which of the following processes can be used to create new species or breeds with distinct genetic characteristics?

• (1). Fusion of protoplasts from two species into hybrid cells, followed by culturing for division and regeneration into organisms, and then propagation into lines.
• Correct. Protoplast fusion creates hybrid cells carrying chromosomes from both species, leading to new species or breeds with distinct traits.
• (2). Culturing a tissue sample of a plant variety in vitro to produce numerous callus tissues, followed by regeneration into complete plants.
• Incorrect. Tissue culture produces offspring with the same genotype as the parent plant, not new species or breeds.
• (3). Cultivating pollen grains to develop haploid plants, then doubling them, and propagating into lines.
• Correct. Pollen culture creates haploid lines, which can be doubled to create homozygous lines with distinct genetic characteristics, potentially leading to new breeds.
• (4). Inducing mutations, selecting individuals with desired phenotypes, and then propagating into lines.
• Correct. Induced mutations create new genetic variations, and selecting desirable phenotypes can lead to the development of new species or breeds.
• Note: Protoplast fusion, pollen culture, and mutation induction are methods for creating new species or breeds with distinct genetic characteristics. Tissue culture produces genetically identical offspring.