NIOS Class 10 Science & Technology Chapter 25 Solution

NIOS Class 10 Science & Technology Chapter 25 Solution – Heredity

NIOS Class 10 Science & Technology Solution Chapter 25 Heredity. NIOS Class 10 Science & Technology Chapter 25 Question Answers Download PDF. NIOS Class 10 Science Notes.

NIOS Class 10 Science & Technology Chapter 25 Solution

Board NIOS
Class 10th (Secondary)
Subject  Science and Technology (252)
Topic Question Answer, Solution, Notes







1)What is meant by the terms (1) Heredity and (2) Variation.

Ans: –Heredity: – In this theory the similar characters transfer from one generation to other generation.

Variation: – Differences in gene combinations among the all the population of a community.


2)Why is Mendel considered as the founder or father of genetics?

Ans: – Mendel is the first scientist who described about the heredity and the gene theory so he knows as father of genetics.


3)Formulate a sentence to demonstrate your understanding of the terms‘dominant’ and ‘recessive.’

Ans: –Dominant: – The gene which express more other than the presence of the other gene is known as dominant.

Recessive: – When absence of the dominant gene is seen then that know as recessive.


4)Name the scientist who discovered that Mendelian factors are present on chromosomes.

Ans: –  Sutton discovered that mentalism factors are present on chromosome.


5)Give the synonym for Mendelian factor.

Ans: – Gene is the synonym for Mendelian factor.



1) Name the sex chromosomes.

Ans: – In human being there are 22 pairs or 44 chromosomes in which 2 are sex chromosome.


2)How many autosomes do humans have?

Ans: – There are 44 autosomes in human being.


3)Why does an organism (except bacteria) have diploid number of chromosomes?

Ans: – As one chromosome of a pair is received from father and one from the mother in organism except bacteria diploid number of chromosomes present.


4)State any two typical features of chromosomes.

Ans: – The typical features of chromosomes are-

  • It bears the genetic characteristics.
  • Itpresents in fixed number in human or any other animal.


5) Define a gene with respect to its chemical nature.

Ans: – Gene is nothing but the DNA or deoxyribonucleic acid which bear the genetic characteristics from one generation to the other.


6)State the three major steps in DNA replication.

Ans: – • Unwinding of the double helix structure of DNA.

  • Formation of DNA complimentary to each DNAstrand in the body.
  • new and one parental DNA strand are formed.


7)Why is DNA fingerprinting a fool proof test?

Ans: –  As we all know that in every human being each one has unique DNA structure so it helps in fingerprint test.




1) What is a gene made of?

Ans: – Gene made off with the DNA or deoxyribonucleic acids.


2)To which blood group would a person having genes IAi belong?

Ans: –  The gene IAi belongs to the blood group A.


3) If a Y bearing sperm fuses with an egg, what will be the sex of the individual developing from the zygote?

Ans: – As we all know Y chromosome denotes the male and X denotes female so, here zygote is male.


4)How many X chromosomes can be found in the cells of the body of (i) a boy,and (ii) a girl.

Ans: – In a boy there are one X and one Y chromosome present and, in a girl,there are 2 X chromosome are present.


5)How many molecules of DNA are present in one chromosome?

Ans: – In a chromosome only one molecules of DNA is present.



1)What will be the blood group of an individual with genetic combination IA IB?

Ans: – The genetic combination of IA and IB represent the blood group AB.


2)How can a person be normal for a trait even when carrying one defective gene for that trait?

Ans: – As this defective gene is recessive in that combination and the other is present in dominant proportion as compared to this so they will be normal.


3)Which is the safest blood group for donation if an accident victim of anunknown blood group has to be given immediate blood transfusion?

Ans: – O positive is the safest blood group for the donation of blood in unknown situation.


4)On which kind of chromosome, the autosomes or the sex chromosomes, are defective genes causing, Thalassemia, colour blindness and Haemophilia located?

Ans: –

  • Thalassemia – autosome.
  • colour blindness andhaemophilia- X chromosome.

5)Name the therapy in which a defective gene is substituted by a normal gene.

Ans: – In a gene replacement therapy the defective gene is substituted by a normal gene.


6) The given box diagram represents the ratio of females to males or the sex ratio in our country for 10 decades (1901 to 2001). Answer the following questions in the light of your knowledge of sex determination and the data presented in the box diagram.

  • What does the bar diagram show?

Ans: – The female population as compared in decade is present in the bar diagram.

  • As per scientific knowledge regarding sex determination, what should be the sex ratio or the male to female ratio at a given point of time.

Ans: – The sex ratio of male and female is 1:1.

  • Assign one reason to the trend showing deviation from the expected sex ratio.

Ans: – The deviation of the expected sex ratio is because of the female foeticide.

  • In what ways is such a trend unfavourable?

Ans: – When male to female ratio is lopsided then this trend will be unfavourable.

  • Suggest a way by which such a trend can be stopped.

Ans: – If we increase the awareness in the rural area about importance of the girls child as boys so then we stopped this way.

  • Do you notice any reversal in the trend? What would you attribute it to?

Ans: – The basic education is needed for the gaining of better results as well as awareness in the different area specifically in the rural are where most case are seen.



1) Which statement is true for ‘genes? Select the correct answer

(a) Genes are imaginary factors.

(b) Genes are fragments of DNA.

(c) Genes are present in the cytoplasm.

(d) Genes are not inherited.

Ans: –Option(b).


2) What are “factors” named by Mendel called today?

Ans: – The factors named by Mendel is gene.


3) What is the chemical nature of a gene? Name the three components of this chemical.

Ans: – The chemical name of gene is deoxyribonucleic acid.

The compound which is present in this are carbon, phosphate group, base like thiamine.


4)Where are genes located?

Ans: –  In the chromosome of human being gene is located.


5)State two differences between autosomes and sex chromosomes.

Ans: –

autosome Sex chromosome
The are 44 in numbers This are 2 in numbers
They don’t help in differentiate in male and female. They helped in gaining the characteristics in male, female.


6)Define heredity, variation, genetic disorder and sex chromosomes.

Ans: – Heredity is the transferred of genetic characteristics from one generation to the next generation.

Variation is the presence of different genetic characteristics in different people.

When there is disorder because of the effect of gene is known as genetic disorder.

The two-chromosome present in male and female which tells us the difference about them is sex chromosome.


7)Why does DNA have to be duplicated before cell division?

Ans: – The gene always get divided into two types one is after the mitosis cell division. These duplicate of one is parent cell and daughter cell which passed.


8)Mention the main steps in DNA replication.

Ans: – As we know in a biological process the DNA is creates its duplicate by which process is known as the DNA replication.


9)What will be the blood group of the following which contain the genes IAi.

Ans: – The blood group of the following IAi genesis group A.


10)Why is haemophilia found mostly in boys?

Ans: – The disease haemophilia is the genetic disorder of chromosome X and as in male there are two X chromosome so the probability of this disease is most.


11) With the help of a line diagram explain the chromosomal basis of a zygote developing into a male child.

Ans: –

12) What is the basis of sex determination in humans?

Ans: –The basic sex determination in human is XX for the male and XY for the female and total 44 chromosome present.


13)Write notes on any one genetic disorder.

Ans: –  The genetic disorder is the disease which happens after any chromosomal disorder like the haemophilia which is a genetic disorder mostly present in male.


14)What is meant by “gene replacement therapy”?

Ans: – With the help of genetic engineering the gene which is faulty or affected is replace by the other gene and this vector is transferred which is known as gene replacement theory.


15) Rahul’s maternal grandfather (mother’s father) was colour-blind. What are the chances of Rahul being colour-blind if his father has normal colour vision?

Ans: –

Updated: March 3, 2022 — 4:53 pm

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