Comprehension:
Mendelian genetics
Read the following passage carefully and answer the given questions.
In Mendel's monohybrid cross between pure tall (TT) and pure dwarf (tt) pea plants, the F1 generation consisted of all tall plants, including dominance of T over t. The tall and dwarf traits were identical to their parental type and did not show any blending. Selfing of F1 plants produced F2 generation in the ratio of 3 Tall: 1 dwarf, whereas genotypic ratio was 1TT : 2Tt : 1tt. Mendel concludes that alleles segregate during gamete formation and one allele from each parent is transmitted to offspring. Also, based on these observations, Mendel proposed that something was being stably passed down, unchanged, from parent to offspring through the gametes, over successive generations. He called these things as ‘factors’. Now we call them as genes as unit of inheritance. The production of gametes by the parents, the formation of the zygotes, the F1 and F2 plants can be understood from a diagram called Punnett Square.
Which one of the following pairs of allele is dominant?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → TT
Mendel’s symbols use a capital letter for the dominant allele and a small letter for the recessive allele. A pair is a dominant pair when both alleles are dominant, so the trait is expressed.
(1) TT — Correct. Both alleles are dominant, so the plant is tall.
(2) tt — Incorrect. Both alleles are recessive. This is the dwarf plant.
(3) yy — Incorrect. Both alleles are recessive. In the pea, yy gives green seeds, while the dominant Y gives yellow seeds.
(4) rr — Incorrect. Both alleles are recessive. In the pea, rr gives wrinkled seeds, while the dominant R gives round seeds.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.