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.
Twenty two pairs of chromosomes which are exactly same in both male and female human beings are called:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Autosomes
A human cell has 23 pairs of chromosomes. Of these, 22 pairs are the same in males and females. They are called autosomes. The remaining pair is the sex chromosomes: XX in the female and XY in the male.
(1) Nucleosomes — Incorrect. A nucleosome is a unit of chromatin. It is made of DNA wound around a core of eight histone molecules. It is not a chromosome.
(2) Autosomes — Correct. Autosomes are the 22 pairs common to both sexes.
(3) Peroxisomes — Incorrect. Peroxisomes are small cell organelles in the cytoplasm, not chromosomes.
(4) Ribosomes — Incorrect. Ribosomes are the cell organelles where proteins are made.
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:
Sex Determination in Humans – “It has already been mentioned that the sex determining mechanism in case of humans is XY type. Out of 23 pairs of chromosomes present, 22 pairs are exactly same in both males and females; these are the autosomes. A pair of X-chromosomes are present in the female, whereas the presence of an X and Y chromosome are determinant of the male characteristic.”