Unit 1: Introduction to Genetics, Mendelian Genetics and Chromosomal Basis of Inheritance - Practice Quiz

1 What is the branch of biology that studies heredity and variation in organisms called?

2 An allele that expresses its trait even in the presence of a contrasting allele is called:

3 A recessive trait is expressed in the phenotype only when the allele is present in which condition?

4 The genetic makeup of an organism for a particular trait is known as its:

5 Which organism did Gregor Mendel use for his classic experiments on inheritance?

6 In a monohybrid cross between two heterozygous tall pea plants (), what is the phenotypic ratio in the generation?

7 According to the Law of Segregation, the two alleles of a gene separate during:

8 What is the genotypic ratio obtained in the generation of a Mendelian monohybrid cross?

9 Two organisms with the same phenotype but different genotypes for a trait are best explained by which concept?

10 What phenotypic ratio is expected in the generation of a dihybrid cross following independent assortment?

11 The Principle of Independent Assortment states that alleles of different genes assort:

12 A cross involving two pairs of contrasting traits is known as a:

13 Which organism did Thomas Hunt Morgan use in his genetic experiments?

14 Morgan's discovery that certain genes are inherited together supported the concept of:

15 The white-eye mutation studied by Morgan in Drosophila was located on which chromosome?

16 The Chromosomal Theory of Inheritance was proposed by:

17 According to the Chromosomal Theory of Inheritance, Mendel's 'factors' (genes) are located on:

18 Chromosomes that are not involved in determining the sex of an organism are called:

19 Which pair of sex chromosomes is normally found in a human male?

20 Which of the following is a common example of a sex-linked recessive disorder in humans?

21 In pea plants, tall () is dominant over dwarf (). A tall plant of unknown genotype is crossed with a dwarf plant, and the offspring are all tall. What is the most likely genotype of the tall parent?

22 A heterozygous purple-flowered plant () is self-pollinated. What fraction of the offspring are expected to be homozygous recessive?

23 The Law of Segregation is best explained physically by which cellular event?

24 In a dihybrid cross , what fraction of offspring are expected to show both recessive phenotypes?

25 How many genetically distinct gamete types can an individual with genotype produce, assuming all genes assort independently?

26 A dihybrid cross yields a phenotypic ratio of . Independent assortment of the two genes requires that they be located:

27 In Morgan's experiments, a white-eyed male fly was crossed with a red-eyed female. What eye colour appeared in the generation?

28 Morgan chose Drosophila melanogaster as a model organism largely because it:

29 Morgan's finding that eye colour in Drosophila was inherited along with sex provided direct evidence that:

30 Which observation formed a key parallel that Sutton and Boveri used to link Mendel's factors to chromosomes?

31 According to the chromosomal theory of inheritance, the diploid number is restored in offspring by which process?

32 Two parents with normal pigmentation have a child with albinism (an autosomal recessive condition). What are the genotypes of the parents?

33 For an autosomal dominant disorder, an affected heterozygous parent married to an unaffected parent has what probability of producing an affected child?

34 Which feature typically distinguishes an autosomal recessive trait in a pedigree?

35 A colour-blind man (X-linked recessive) marries a woman who is a carrier. What proportion of their sons are expected to be colour-blind?

36 Why are X-linked recessive disorders such as haemophilia far more common in males than in females?

37 A carrier mother () for an X-linked recessive trait marries an unaffected father (). What fraction of their daughters are expected to be carriers?

38 A trait is passed from an affected father to all of his daughters but to none of his sons. This pattern most likely indicates:

39 A test cross of a purple-flowered plant produces offspring in a ratio of purple : white. What does this reveal about the tested plant?

40 In humans, the ability to roll the tongue is autosomal dominant. Two tongue-rolling parents produce a non-roller child. The genotypes of the parents must be:

41 In a dihybrid cross , a student expects a ratio but observes a ratio in the for a single trait (e.g., flower pigment). What is the most likely explanation?

42 A trihybrid cross is performed with all genes assorting independently and each showing complete dominance. What fraction of the offspring will be homozygous recessive for at least one of the three genes?

43 A color-blind woman marries a man with normal color vision. Regarding their children (color blindness is X-linked recessive), which statement is correct?

44 In Morgan's experiments, a cross between white-eyed females () and red-eyed males () produced red-eyed daughters and white-eyed sons. This 'crisscross' inheritance pattern most directly supports which conclusion?

45 Two normally pigmented parents have an albino child (albinism is autosomal recessive). If they have three more children, what is the probability that exactly two of the three are albino?

46 In a testcross where the genes are linked with 20% recombination frequency, what proportion of offspring are expected to be the parental (non-recombinant) types combined?

47 A heterozygote shows a phenotype intermediate between the two homozygotes. Which single conclusion is most strictly justified by this observation alone?

48 In cats, coat color is X-linked: (orange) and (black) are codominant, producing tortoiseshell in heterozygotes. Why are tortoiseshell cats almost always female?

49 A plant of unknown genotype with a dominant phenotype () is testcrossed. Among 100 offspring, 100 show the dominant phenotype. What is the best statistically supported conclusion about the parent?

50 The chromosomal theory of inheritance proposed that genes reside on chromosomes. Which observation provided the most direct physical evidence linking a specific gene to a specific chromosome?

51 For a cross with independent assortment and complete dominance at all loci, how many different phenotypes are possible in the generation?

52 In a pedigree, an affected child is born to two unaffected parents, and the trait appears in both males and females roughly equally, sometimes skipping generations. Which inheritance pattern is most consistent?

53 Hemophilia is X-linked recessive. A phenotypically normal woman whose father was a hemophiliac marries a normal man. What is the probability that their first child is a hemophiliac son?

54 In snapdragons, red () white () gives pink . If pink are crossed with white plants, what phenotypic ratio is expected?

55 Morgan crossed red-eyed heterozygous females () with red-eyed males (). Among the , which eye-color/sex combination should be completely absent?

56 A dihybrid organism produces gametes. If the two genes are on the same chromosome and completely linked (no crossing over), what gamete types and proportions are produced?

57 In humans, the ABO blood group shows multiple alleles: and codominant, both dominant over . A cross between an father and an mother is possible. What fraction of children could have blood type O?

58 A recessive allele causes a metabolic disorder only in homozygotes, yet heterozygous carriers show slightly reduced enzyme activity detectable by lab tests. At the biochemical level, how is this trait best described?

59 Which parallel between gene behavior (Mendel's laws) and chromosome behavior (meiosis) was the central logical foundation of Sutton and Boveri's chromosomal theory?

60 A gene is located in the pseudoautosomal region shared by both the X and Y chromosomes. How would inheritance of a recessive allele in this region differ from a standard X-linked recessive allele?