Free Mendel's Laws of Inheritance MCQs with Answers

41. Polygenic inheritance involves

• A. One gene with two alleles
• B. Multiple genes affecting one trait
• C. Genes on sex chromosomes only
• D. Mitochondrial genes

Explanation: Polygenic traits (height, skin color) are controlled by multiple genes, showing continuous variation.

42. Pleiotropy refers to

• A. One gene affecting multiple traits
• B. Multiple genes affecting one trait
• C. Genes on same chromosome
• D. Genes affecting only one tissue

Explanation: Pleiotropy is when one gene affects multiple phenotypic traits, e.g., sickle cell gene affects multiple organs.

43. Self-fertilization in plants through successive generations can lead to the development of:

• A. Hybrid breeds of plants
• B. Variations in coming generation
• C. True breeding plants
• D. Adaptation with their environment

Explanation: Repeated self pollination steadily removes heterozygotes, since each generation halves their proportion, until the line is homozygous and breeds true for every character. This is exactly how Mendel obtained the pure lines his experiments depended on. Hybrids and new variation arise from cross fertilisation, which is the opposite process.

44. In a pea plant seed color is determined by two alleles: Y (Yellow, dominant) and y (green, recessive). Which parental cross would most likely result in offspring showing a 1:1 ratio of yellow to green seeds?

• A. Yy x YY
• B. Yy x yy
• C. Yy x Yy
• D. YY x yy

Explanation: Crossing a heterozygote with a homozygous recessive gives half Yy and half yy, that is one yellow to one green, which is the classic test cross. Yy by Yy gives three yellow to one green, and any cross involving YY gives all yellow because every offspring receives at least one dominant allele. Recognising the test cross by its 1:1 outcome is the quickest route.

45. Mendel crossed a plant with round yellow seeds (RRYY) and a plant with wrinkled green seeds (rryy), what was the phenotype of all F1 offspring?

• A. All round green
• B. All round yellow
• C. All wrinkled yellow
• D. All wrinkled green

Explanation: Every offspring receives R and Y from one parent and r and y from the other, so all are RrYy and both dominant characters show, giving round yellow seeds. The recessive wrinkled and green phenotypes reappear only in the F2, in the familiar 9:3:3:1 ratio. This uniform F1 is what Mendel's law of dominance describes.