Biology: Heredity

31. How many chromosomes are there in humans? [U.P.P.C.S. (Pre) 1992, U.P.P.C.S. (Pre) 1991]

(a) 36
(b) 46
(c) 56
(d) 26

Correct Answer: (b) 46

Solution:

In humans, each cell normally contains 23 pairs of chromosomes, a total of 46. Twenty-two of these pairs called autosomes which are the same in both males and females. The 23rd pair, the sex chromosomes differ between males and females. Females have two copies of the X chromosome (XX) while males have one X and one Y chromosome (XY).

32. The number of chromosome pairs, found in the cells of human body is— [Uttarakhand P.C.S. (Pre) 2003]

(a) 21
(b) 22
(c) 23
(d) 24

Correct Answer: (c) 23

Solution:

In humans, each cell normally contains 23 pairs of chromosomes, a total of 46. Twenty-two of these pairs called autosomes which are the same in both males and females. The 23rd pair, the sex chromosomes differ between males and females. Females have two copies of the X chromosome (XX) while males have one X and one Y chromosome (XY).

33. Assertion (A) : In human being, the females play a major role in determining the sex of the offspring. [I.A.S. (Pre) 2000]

Reason (R) : Women have two 'X' chromosomes.

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not a correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Correct Answer: (d) (A) is false but (R) is true.

Solution:The X chromosome is one of the two sex-determining chromosomes (allosomes) in many animal species, including mammals and is found in both males and females. Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes (XX) whereas males have one X and one Y chromosome (XY). X of male and X of female give birth to a female child (44+XX) whereas Y of male and X of female give birth to a male child (44+XY) Thus, in human being, the males play a major role in determining the sex of the offspring

34. Male's gene constituent is — [43rd B.P.S.C. (Pre) 1999]

(a) XX
(b) XY
(c) X
(d) Y

Correct Answer: (b) XY

Solution:The X chromosome is one of the two sex-determining chromosomes (allosomes) in many animal species, including mammals and is found in both males and females. Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes (XX) whereas males have one X and one Y chromosome (XY). X of male and X of female give birth to a female child (44+XX) whereas Y of male and X of female give birth to a male child (44+XY) Thus, in human being, the males play a major role in determining the sex of the offspring

35. Which combination of chromosomes in mankind give birth to a male child? [M.P.P.C.S. (Pre) 2005]

(a) X of male and X of female
(b) X of male and Y of female
(c) Y of male and X of female
(d) Y of male and Y of female

Correct Answer: (c) Y of male and X of female

Solution:

The X chromosome is one of the two sex-determining chromosomes (allosomes) in many animal species, including mammals and is found in both males and females. Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes (XX) whereas males have one X and one Y chromosome (XY). X of male and X of female give birth to a female child (44+XX) whereas Y of male and X of female give birth to a male child (44+XY). Thus, in human being, the males play a major role in determining the sex of the offspring.

36. Which of the following professional(s) are more likely to run the risk of a permanent change in their cell's DNA? [I.A.S. (Pre) 1996]

Researchers using carbon 14 isotope
X-ray technician
Coal miner
Dyer and painter

Select the correct answer by using the codes given below :
Code :

(a) 2 only
(b) 1, 2 and 3
(c) 1, 2 and 4
(d) 1, 3 and 4

Correct Answer: (a) 2 only

Solution:X-ray technicians are more likely to run the risk of a permanent change in their cell’s DNA as compared to others due to their regular exposure to ionizing radiation from X-ray machines. X-rays are a form of ionizing radiation, which means they carry enough energy to knock electrons off atoms, potentially damaging DNA. This repeated exposure can lead to DNA damage, including breaks and mutations, which can disrupt normal cell function.

Biology: Heredity

31. How many chromosomes are there in humans? [U.P.P.C.S. (Pre) 1992, U.P.P.C.S. (Pre) 1991]

32. The number of chromosome pairs, found in the cells of human body is— [Uttarakhand P.C.S. (Pre) 2003]

33. Assertion (A) : In human being, the females play a major role in determining the sex of the offspring. [I.A.S. (Pre) 2000]

34. Male's gene constituent is — [43rd B.P.S.C. (Pre) 1999]

35. Which combination of chromosomes in mankind give birth to a male child? [M.P.P.C.S. (Pre) 2005]

36. Which of the following professional(s) are more likely to run the risk of a permanent change in their cell's DNA? [I.A.S. (Pre) 1996]

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