PAGE 2 Question1. What is a gene? (1 marks)
Answer. Gene is the unit of inheritance. Gene is the part of a chromosome which controls the appearance of a set of hereditary characteristics.
Question2. What is a sex chromosome? [2 marks]
Answer. Sex chromosome is a chromosome that operates in the sex-determining mechanism of a species. Many animals have two different types of sex chromosomes. For example, in human there is a large X chromosome and a much smaller Y chromosome.
Question3. .”The sex of the children is determined by what they inherit from their father and not their mother.” Justify. [2 marks]
Answer. It is because a child who inherits an X chromosome from her father will be a girl and one who inherits a Y chromosome from his father will be a boy. But all children inherit a X chromosome from their mother regardless of whether they are boys or girls.
Question4.Define variation in relation to a species. Why is variation beneficial to the species? [3 marks]
Answer. Variation refers to the differences in the characters or traits among the individuals of a species.
Variations are beneficial to the species because:
1. They enable the organisms to adapt themselves in changing environment.
2. Variations form the basis of heredity.
3. They form the raw materials for evolution and development of new species.
Question5. Distinguish between acquired and inherited traits by giving one example of each. Why are traits acquired during the lifetime of an individual not inherited? [3 marks]
Answer. Acquired trait is a particular characteristic that is developed during the lifetime of an individual. Such characteristics are not genetically controlled and cannot be passed on to the next generation. Example: Loss of weight due to starvation.
Inherited trait is the transmission of particular characteristics from parents to their off springs, generation to generation. Such traits are genetically determined characteristic that distinguishes a person.
Question6. . Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters. [2 marks]
Answer. Eye colour or hair colour of a person is an example of inherited character whereas, body weight is an example of acquired character.
The basic difference between inherited and acquired character is that inherited character is passed on from parent to offspring and acquired characters are acquired by an individual during his lifetime depending upon his lifestyle.
Question7. Explain the mechanism of sex determination in humans. [2 marks]
Or
With the help of a flow chart explain in brief how the sex of a newborn is genetically determined in human beings. Which of the two parents, the mother or the father, is responsible for determination of sex of a child? [Foreign]
Answer. Mechanism of Sex Determination in Human Beings:
In human beings, the sex of the individual is genetically determined.
Sex determination is the process by which sex of a new born individual can be determined.
Human beings have 1 unpaired sex chromosome. Sex chromosome of male is XY and of female is XX.
Sex of a child depends on what happens at fertilisation.
heredity-and-evolution-chapter-wise-important-questions-class-10-science-1
Thus, father is responsible for the determination of the sex of a child.
Question8. Why is DNA copying necessary during reproduction?
Answer:
DNA copying is necessary during reproduction as DNA carries genetic information. Therefore, for an organism to produce similar offsprings it is necessary to copy DNA.
Question9. Define chromosome.
Answer:
Chromosome is a thread-like structure that bears genes and are enclosed within a nucleus. It is composed of DNA and protein.
Question10.
Can you justify the statement that “Human
males are responsible for determining the sex of the baby and not
females”? [CBSE 2012, 2013]
Answer:
The sex in human beings or the sex of the individual is largely genetically
determined. A male cell has two types of sex chromosomes i.e., X – chromosome
and Y – chromosome because of which male produces two types of sperms with
genotype A + X and A + Y. Female cells have two X – chromosomes so the genotype
of eggs produced by her is A + X. During fertilisation the chances are:
·
If a sperm carrying Y
– chromosome fertilises the egg, then the child born will be a male i.e., AA +
XY.
·
If a sperm carrying X
– chromosome fertilises the egg then the child born will be a female i.e., AA +
XX.
Thus we can infer that the sperm of the male
determines the sex of the child.
