Inheritance and variation
Read the following passage carefully and answer the given questions.
Mendel’s approach of using mathematics to explain biological phenomena was totally new and unacceptable to many of the biologists of his time. Finally, though Mendel’s work suggested that factors (genes) were discrete units, he could not provide any physical proof for the existence of factors or say what they were made of. In the dihybrid cross, the phenotypes round, yellow; wrinkled, yellow; round, green and wrinkled, green appeared in the ratio 9:3:3:1. Such a ratio was observed for several pairs of characters that Mendel studied. The important things to remember are that chromosomes as well as genes occur in pairs. Morgan and his group also found that even when genes were grouped on the same chromosome, some genes were very tightly linked while others were loosely linked. In a number of other insects and mammals including man, XY type of sex determination is seen where both male and female have same number of chromosomes. Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.
The scientists, who independently rediscovered Mendel’s results on the inheritance of characters were:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → de Vries, Correns and von Tschermak
Mendel published his work on inheritance in 1865, but for many years it was not accepted. In 1900, three scientists, de Vries, Correns and von Tschermak, working separately, rediscovered his results on the inheritance of characters.
(1) Walter Sutton and Theodore Boveri — Incorrect. They noted that chromosomes behave like Mendel’s factors. Sutton joined this with Mendel’s laws to give the chromosomal theory of inheritance.
(2) de Vries, Correns and von Tschermak — Correct. They rediscovered Mendel’s results independently in 1900.
(3) Thomas Hunt Morgan and his colleagues — Incorrect. Morgan tested the chromosomal theory with experiments on the fruit fly Drosophila melanogaster. His work gave the ideas of linkage and recombination.
(4) Oswald Avery, Colin MacLeod and Maclyn McCarty — Incorrect. They worked out the chemical nature of Griffith’s transforming principle and showed that it is DNA.
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.
NCERT Extract:
Chromosomal Theory of Inheritance – …
