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NIOS Class 10 Science and Technology Chapter 25 Heredity
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Heredity
Chapter: 25
INTEXT QUESTIONS 25.1
1. What is meant by the terms.
(i) Heredity.
Ans: (i) Passing down of similar characters generation after generation.
(ii) Variation.
Ans: Differences in gene combinations.
2. Why is Mendel considered as the founder or father of genetics?
Ans: He had initiated work on heredity/genetics.
3. Formulate a sentence to demonstrate your understanding of the terms ‘dominant’ and ‘recessive.’
Ans: (i) The gene which may express in spite of the presence of the other (Dominant).
(ii) Expression only in the absence of the dominant gene. (Recessive).
4. Name the scientist who discovered that Mendelian factors are present on chromosomes.
Ans: Sutton.
5. Give the synonym for Mendelian factor.
Ans: Gene.
INTEXT QUESTIONS 25.2
1. Name the sex chromosomes.
Ans: X and Y.
2. How many autosomes do humans have?
Ans: 22 pairs or 44 chromosomes.
3. Why does an organism (except bacteria) have diploid number of chromosomes?
Ans: Because one chromosome of a pair is received from father and one from the mother.
4. State any two typical features of chromosomes.
Ans: Two typical features of chromosomes are mentioned below:
(i) present in pairs.
(ii) seen only during cell division.
5. Define a gene with respect to its chemical nature.
Ans: Genes are segments of a DNA molecule. So it is made of Deoxyribonucleic acid or DNA.
6. State the three major steps in DNA replication.
Ans: The there major steps in DNA relocation are mentioned are below:
(i) Unwinding of double helix.
(ii) Formation of new molecules of DNA complimentary to each DNA strand.
(iii) Winding of one new and one parental DNA strand.
7. Why is DNA fingerprinting a fool proof test?
Ans: Because DNA of every individual is unique.
INTEXT QUESTIONS 25.3
1. What is a gene made of?
Ans: DNA.
2. To which blood group would a person having genes IAi belong?
Ans: 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: Male.
4. How many X chromosomes can be found in the cells of the body of
(i) A boy.
Ans: For boy – 44 autosomes and one X and one Y chromosomes.
(ii) A girl.
Ans: For girls – 44 autosomes and 2 X chromosomes.
5. How many molecules of DNA are present in one chromosome?
Ans: One molecule of DNA.
INTEXT QUESTIONS 25.4
1. What will be the blood group of an individual with genetic combination IA IB?
Ans: AB.
2. How can a person be normal for a trait even when carrying one defective gene for that trait?
Ans: The other member of the pair is dominant and masks the effect of the recessive gene.
3. Which is the safest blood group for donation if an accident victim of an unknown blood group has to be given immediate blood transfusion?
Ans: ‘O’ positive.
4. On which kind of chromosome, the autosomes or the sex chromosomes, are defective genes causing, Thalassemia, colour blindness and Haemophilia located?
Ans: Thalassemia – autosomal, colour blindness and haemophilia on X chromosome.
5. Name the therapy in which a defective gene is substituted by a normal gene.
Ans: Gene replacement therapy.
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.
(i) What does the bar diagram show? _________________.
Ans: Bar diagram shows the proportion of females in the population over a decade.
(ii) 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: 1:1
(iii) Assign one reason to the trend showing deviation from the expected sex ratio. _________.
Ans: Female foeticide.
(iv) In what ways is such a trend unfavourable? _____________________.
Ans: Male to female ratio becomes lopsided
(v) Suggest a way by which such a trend can be stopped. ___________________.
Ans: Banning sex tests of unborn baby; increasing awareness.
(vi) Do you notice any reversal in the trend? What would you attribute it to?
Ans: Yes, awareness and education/ No- with reasons.
| TERMINAL EXERCISES |
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: (b) Genes are fragments of DNA.
2. What are “factors” named by Mendel called today?
Ans: According to the modern concept, Mendel’s factor is called a gene. Mendel believed that heredity is the result of discrete units of inheritance, and every single unit (or gene) was independent in its actions in an individual’s genome.
3. What is the chemical nature of a gene? Name the three components of this chemical.
Ans: The chemical name of the gene is deoxyribonucleic acid.
The compound which is present in this are carbon, phosphate group, base like thiamine.
4. Where are genes located?
Ans: Genes are located in the chromosomes.
5. State two differences between autosomes and sex chromosomes.
Ans: Two differences between autosomes and sex chromosomes are mentioned below:
| Autosomes | Sex chromosomes |
| Chromosomes that are NOT directly related to the sex of an organism. | The set of chromosomes that directly control the development of sexual characteristics. |
| Homologous chromosomes are two chromosomes (one from each parent) that have the same size and the same genes on each. | In humans and all mammals, the XY system determines sex. XX = female and XY = male. |
6. Define.
(i) Heredity.
Ans: The passing down of characters from parents to offspring is termed heredity. Heredity is controlled by genes.
(ii) variation.
Ans: (a) The act or process of varying: the state or fact of being varied.
(b) an instance of varying.
(c) the extent to which or the range in which a thing varies.
(iii) Genetic disorder.
Ans: Genetic disorders is a category of diseases that includes certain types of birth defects, chronic diseases, developmental problems, and sensory deficits that are inherited from one or both parents.
(iv) sex chromosomes.
Ans: A sex chromosome is a type of chromosome involved in sex determination.
7. Why does DNA have to be duplicated before cell division?
Ans: It is important that DNA is duplicated prior to cell division because it ensures that the daughter cells get the correct amount of DNA. In eukaryotic cells, mitosis is the process of cell division. It creates two identical daughter cells from one parent cell.
8. Mention the main steps in DNA replication.
Ans: The main steps in DNA replication are mentioned below:
(i) The double stranded DNA molecule unwinds with the help of certain enzymes to expose two strands of DNA.
(ii) A DNA polymerase enzyme catalyses the formation of a new daughter strand which can form a double helix with one strand of parental DNA molecule. So two DNA molecules, each with a parental strand and a new strand get generated.
(iii) The two identical DNA molecules then become two chromatids which remain attached by a centromere.
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 chromosomes 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 sex of the baby is determined by the type of male gamete that fuses with the female gamete. If the fertilising sperm contains X chromosome, then the baby produced will be a girl and if the fertilising sperm contains Y chromosome, then the baby produced will be a boy.
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: Gene therapy is a technique that uses a gene(s) to treat, prevent or cure a disease or medical disorder. Often, gene therapy works by adding new copies of a gene that is broken, or by replacing a defective or missing gene in a patient’s cells with a healthy version of that gene.
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: Do your self.
