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Question 1. Which principle states that each parent contributes one allele for a given trait, and these alleles segregate during gamete formation? A) Law of Independent Assortment B) Law of Dominance C) Law of Segregation D) Law of Linkage Answer: C Explanation: The Law of Segregation, proposed by Mendel, describes the separation of paired alleles into different gametes. Question 2. In Mendelian terminology, the observable characteristic of an organism is called its: A) Genotype B) Phenotype C) Allele D) Karyotype Answer: B Explanation: Phenotype refers to the physical expression of genetic information, whereas genotype is the underlying genetic makeup. Question 3. A plant that is true-breeding for yellow seed color (YY) is crossed with a true-breeding white seed plant (yy). What proportion of the F1 offspring will be heterozygous? A) 0% B) 25% C) 50% D) 100% Answer: D Explanation: All F1 individuals inherit one Y allele from the yellow parent and one y allele from the white parent, making them all Yy.
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Question 4. If two genes are located on different chromosomes, which Mendelian law predicts their segregation? A) Law of Dominance B) Law of Segregation C) Law of Independent Assortment D) Law of Linkage Answer: C Explanation: The Law of Independent Assortment states that alleles of different genes assort independently when the genes are on separate chromosomes. Question 5. In a monohybrid cross, a heterozygous (Rr) individual is crossed with a homozygous recessive (rr). What is the expected phenotypic ratio in the offspring? A) 3: B) 1: C) 1:2: D) 2: Answer: B Explanation: The cross yields 50% Rr (dominant phenotype) and 50% rr (recessive phenotype), giving a 1:1 ratio. Question 6. Which notation correctly represents a dominant allele and its recessive counterpart for the same gene? A) A / a B) a / a C) A / A D) a / A Answer: A Explanation: Uppercase letters denote dominant alleles, while lowercase letters denote recessive alleles of the same gene.
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Question 10. In a reciprocal cross, the sexes of the parents are switched. Which outcome would indicate that the trait is sex-linked? A) Identical offspring ratios in both crosses B) Different offspring ratios between the two crosses C) No offspring produced in one direction D) All offspring display the dominant phenotype Answer: B Explanation: Sex-linked traits often show different segregation patterns depending on which parent contributes the X chromosome. Question 11. In incomplete dominance, the heterozygote phenotype is: A) Identical to the dominant homozygote B) Identical to the recessive homozygote C) An intermediate between the two homozygotes D) Variable depending on environment Answer: C Explanation: Incomplete dominance produces a blending phenotype, such as pink flowers from red (RR) × white (rr) parents. Question 12. Which blood group system exemplifies codominance? A) ABO B) Rh factor C) MN D) Lewis Answer: C Explanation: In the MN blood group, both M and N alleles are expressed simultaneously on the red cell surface.
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Question 13. In a population where a lethal recessive allele (ll) causes embryonic death, what phenotypic ratio would be observed among surviving offspring from a heterozygous cross (Ll × Ll)? A) 3: B) 2: C) 1: D) 1:2: Answer: B Explanation: The ll genotype is lethal, so only LL, Ll, and Ll survive, giving a 1 LL : 2 Ll ratio (2:1 dominant phenotype to heterozygote phenotype). Question 14. Epistasis occurs when: A) Two alleles at the same locus interact. B) One gene masks the expression of another gene at a different locus. C) Multiple genes additively influence a trait. D) A gene is expressed in only one sex. Answer: B Explanation: Epistatic genes affect the phenotypic expression of other genes, often masking them. Question 15. In a dihybrid cross involving two genes that exhibit recessive epistasis, what phenotypic ratio is expected? A) 9:3: B) 9: C) 12:3: D) 9:3:3: Answer: A Explanation: Recessive epistasis yields a 9:3:4 ratio where the double recessive genotype masks the other phenotypes. Question 16. Pleiotropy refers to:
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C) Autosomal dominant D) Mitochondrial Answer: B Explanation: Y-linked traits are located on the Y chromosome and therefore transmit only from father to son. Question 20. Sex-influenced traits differ from sex-limited traits because: A) They are expressed only in one sex. B) Their expression depends on hormonal environment but can appear in both sexes. C) They are located on autosomes. D) They follow mitochondrial inheritance. Answer: B Explanation: Sex-influenced traits are autosomal but are expressed differently due to sex hormones; sex-limited traits appear only in one sex. Question 21. In a pedigree, a trait that appears in every generation and affects both males and females equally is most consistent with: A) Autosomal recessive inheritance B) X-linked recessive inheritance C) Autosomal dominant inheritance D) Mitochondrial inheritance Answer: C Explanation: Autosomal dominant traits typically manifest in each generation and affect both sexes equally. Question 22. Which pattern of inheritance would you expect for a mitochondrial disease? A) Paternal transmission only B) Maternal transmission only
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C) Equal transmission from both parents D) Sex-linked transmission Answer: B Explanation: Mitochondrial DNA is inherited almost exclusively from the mother. Question 23. Two genes located close together on the same chromosome tend to: A) Assort independently B. Segregate according to the Law of Segregation only C) Be inherited together unless crossing over occurs D) Never recombine Answer: C Explanation: Linked genes travel together during meiosis unless a crossover event separates them. Question 24. In a test cross involving two linked genes A and B (AB/ab × ab/ab), the parental (non-recombinant) phenotypes appear at 40% each, and recombinant phenotypes each appear at 10%. What is the recombination frequency? A) 10% B) 20% C) 30% D) 40% Answer: B Explanation: Recombination frequency = (sum of recombinant offspring / total) × 100 = (10+10)/100 = 20%. Question 25. A recombination frequency of 0% between two loci indicates: A) Complete linkage B) Independent assortment C) Partial linkage
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Answer: A Explanation: Interference = 1 – c; thus 1 – 0.5 = 0.5, indicating moderate interference. Question 29. Genomic imprinting results in: A) Random expression of maternal and paternal alleles. B) Silencing of one allele depending on its parent of origin. C) Equal expression of both alleles. D) Mitochondrial inheritance patterns. Answer: B Explanation: Imprinting epigenetically silences either the maternal or paternal allele, affecting phenotype. Question 30. The “norm of reaction” concept explains: A) Fixed phenotypic expression regardless of environment. B) Variation in phenotype caused by different genotypes only. C) The range of phenotypes a single genotype can produce under varying environments. D) The inheritance of mitochondrial DNA. Answer: C Explanation: The norm of reaction describes how a genotype’s phenotype changes across environmental conditions. Question 31. In a dihybrid cross where both genes show complete dominance and are on different chromosomes, what proportion of the offspring will be heterozygous for both genes? A) 1/ B) 1/ C) 1/ D) 1/ Answer: A
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Explanation: The heterozygous genotype for each gene (AaBb) occurs in 1/4 of the offspring (¼ AA BB, ¼ Aa BB, ¼ AA Bb, ¼ Aa Bb → only one quadrant is AaBb). Question 32. A plant with genotype RrSs (both traits dominant) is self-pollinated. Assuming independent assortment, how many phenotypic classes are expected? A) 4 B) 8 C) 9 D) 16 Answer: C Explanation: For two independently assorting traits each with dominant/recessive phenotypes, the phenotypic ratio is 9:3:3:1, giving four classes. However, because both traits are dominant in the parent, the full phenotypic spectrum (both dominant, one dominant/one recessive, both recessive) comprises 4 classes. The classic 9:3:3:1 ratio yields 4 distinct phenotypes, not 9. The correct answer is A) 4. Question 33. In a backcross of a heterozygous F1 (Aa) to the recessive parent (aa), the expected genotypic ratio is: A) 1 AA : 1 Aa : 1 aa B) 1 Aa : 1 aa C) 1 AA : 2 Aa : 1 aa D) 3 Aa : 1 aa Answer: B Explanation: The cross Aa × aa yields 50% Aa and 50% aa. Question 34. Which of the following statements about the Law of Dominance is FALSE? A) Heterozygotes display the dominant phenotype. B) Dominant alleles completely mask recessive alleles. C) All traits follow complete dominance. D) The law applies to single-gene traits.
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D) Fisher’s exact test Answer: C Explanation: The chi-square goodness-of-fit test assesses how well observed data fit expected Mendelian ratios. Question 38. In a cross where the F2 generation shows a 9:7 phenotypic ratio, which type of gene interaction is most likely? A) Complementary (duplicate) epistasis B) Recessive epistasis C) Dominant epistasis D) Duplicate recessive epistasis Answer: A Explanation: A 9:7 ratio indicates complementary (duplicate) gene interaction where both dominant alleles are required for the phenotype. Question 39. A gene that is lethal when homozygous dominant (AA) but viable as heterozygote (Aa) and homozygous recessive (aa) will produce which phenotypic ratio among surviving offspring from an Aa × Aa cross? A) 3: B) 2: C) 1:2: D) 1: Answer: B Explanation: The AA genotype dies, leaving 2 Aa (dominant phenotype) and 1 aa (recessive phenotype) → 2:1 ratio. Question 40. Which of the following best describes a “test cross” in genetics? A) Crossing two homozygous dominant individuals. B) Crossing a heterozygote with a homozygous recessive individual. C) Crossing two heterozygotes.
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D) Crossing a homozygous recessive with a homozygous dominant individual. Answer: B Explanation: A test cross uses a homozygous recessive partner to uncover the genotype of a dominant-phenotype individual. Question 41. In a pedigree, a trait appears only in males and is transmitted from affected fathers to all their sons, but never to daughters. This pattern suggests: A) X-linked recessive B) X-linked dominant C) Y-linked D) Autosomal recessive Answer: C Explanation: Y-linked traits pass from father to son exclusively. Question 42. The probability of obtaining a genotype AaBb from a dihybrid cross AaBb × AaBb (assuming independent assortment) is: A) 1/ B) 1/ C) 1/ D) 9/ Answer: B Explanation: Probability of Aa = 1/2, Bb = 1/2; combined = 1/2 × 1/2 = 1/4. However, there are two ways to get Aa (A from first parent, a from second, or vice versa) and similarly for Bb, giving 1/4 × 1/4 = 1/16? Let's calculate correctly: For each locus, Aa occurs with probability 1/2. For two loci, probability = 1/2 × 1/2 = 1/4. Therefore answer is A) 1/4. Question 43. In a population, a gene has three alleles (Iⁱ, Iᴬ, i). The blood type AB results from which genotype? A) IⁱIᴬ B) IᴬIᴬ
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B) Only heterozygous C) Both homozygous dominant and heterozygous D) Only homozygous recessive Answer: C Explanation: Complete dominance means that one copy of the dominant allele is sufficient to express the phenotype. Question 47. In a backcross of an F1 heterozygote (Aa) to a homozygous dominant parent (AA), what proportion of offspring will be heterozygous? A) 0% B) 25% C) 50% D) 100% Answer: C Explanation: The cross AA × Aa yields 50% AA and 50% Aa. Question 48. Which of the following best describes “duplicate recessive epistasis”? A) Two genes act independently, each with a dominant allele required for the phenotype. B) Either gene can produce the same phenotype when homozygous recessive. C) One gene masks the effect of another regardless of its genotype. D) Both genes must be dominant for the phenotype to appear. Answer: B Explanation: In duplicate recessive epistasis, having either gene homozygous recessive blocks the phenotype, leading to a 9:7 ratio. Question 49. In a cross between two heterozygous pea plants (Rr) for seed shape, the expected genotypic ratio is: A) 1 RR : 2 Rr : 1 rr B) 3 R_ : 1 rr
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C) 1 RR : 1 rr D) 2 R_ : 2 rr Answer: A Explanation: A monohybrid cross of heterozygotes yields a 1:2:1 genotypic ratio. Question 50. A researcher observes that a particular trait follows a 1: phenotypic ratio in the F2 generation of a dihybrid cross. Which genetic phenomenon most likely explains this observation? A) Independent assortment B) Complete dominance C) Sex-linked inheritance D) Lethal allele affecting one phenotype class Answer: D Explanation: A 1:1 ratio in F2 suggests that one genotype is lethal, removing half of the expected classes. Question 51. In a three-point test cross, the most distant genes are identified by: A) The highest recombination frequency. B) The lowest recombination frequency. C) The number of double crossovers. D) The number of parental types. Answer: A Explanation: Genes farther apart recombine more frequently, giving the highest RF. Question 52. Which of the following is NOT a requirement for a gene to be considered “linked”? A) Located on the same chromosome. B) Segregate independently. C) Proximity reduces recombination frequency.
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C) AB
D) ab Answer: C (or D, depending on parental arrangement) Explanation: Parental gametes retain the original allele combinations; if the parents were AB/ab, the non-recombinant types are AB and ab. Assuming the parental configuration is AB/ab, C) AB is a parental gamete. Question 56. In a test cross for a trait that is X-linked recessive, a heterozygous female (X⁺X) is crossed with a normal male (X⁺Y). What proportion of male offspring will be affected? A) 0% B) 25% C) 50% D) 100% Answer: A Explanation: The male receives his X chromosome from the mother (X⁺) and Y from the father, so none will be affected. Question 57. Which of the following statements about the “sum rule” in probability is correct? A) It is used when events are mutually exclusive. B) It is used when events are independent. C) It calculates the probability of both events occurring together. D) It is only applicable to genetic crosses. Answer: A Explanation: The sum rule adds probabilities of mutually exclusive events because they cannot occur simultaneously. Question 58. A dihybrid cross yields 160 offspring with the following phenotypes: 40 red-round, 40 red-wrinkled, 40 white-round, 40 white-wrinkled. Which conclusion is most appropriate?
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A) Genes are linked with 0% recombination. B) Genes assort independently. C) There is complete dominance with epistasis. D) One gene is lethal. Answer: B Explanation: Equal numbers of all four phenotypic classes indicate independent assortment with no linkage. Question 59. In a backcross of a heterozygous F1 (Aa) to a homozygous recessive (aa), the expected phenotypic ratio is: A) 3 dominant : 1 recessive B) 1 dominant : 1 recessive C) 1 dominant : 3 recessive D) 2 dominant : 2 recessive Answer: B Explanation: The cross yields 50% Aa (dominant phenotype) and 50% aa (recessive phenotype). Question 60. Which of the following is true about “duplicate dominant epistasis”? A) Both genes must be dominant for the phenotype to appear. B) Either dominant allele at one locus can mask the effect of the other locus. C) The phenotype appears only when both loci are homozygous recessive. D) It produces a 9:7 phenotypic ratio. Answer: B Explanation: In duplicate dominant epistasis, a dominant allele at either locus is sufficient to produce the dominant phenotype, leading to a 15:1 ratio. Question 61. In a three-point cross, the double-crossover (DCO) progeny are crucial for determining:
