List of top Science Questions on Heredity and Evolution asked in CBSE Class X, CBSE Compartment X

Consider the following statements:
(i) The sex of a child is determined by what it inherits from the mother.
(ii) The sex of a child is determined by what it inherits from the father.
(iii) The probability of having a male child is more than that of a female child.
(iv) The sex of a child is determined at the time of fertilisation when male and female gametes fuse to form a zygote.
The correct statements are:

Chromosomes:
(i) carry hereditary information from parents to the next generation.
(ii) are thread like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human reproductive cells.
(iv) are involved in the process of cell division.
The correct statements are:

A cross made between two pea plants produces 50% tall and 50% short pea plants. The gene combination of the parental pea plants must be

Assertion (A): Human female has a perfect pair of sex chromosomes.
Reason (R): Sex chromosome contributed by the human male in the zygote decides the sex of a child.

Assertion (A): Sex of the children will be determined by what they inherit from their mother. Reason (R): Women have XX sex chromosomes.

In an experiment to study independent inheritance of two separate traits: shape and colour of seeds, the ratio of the different combinations in F₂ progeny would be

A cross between two tall pea plants resulted in offspring having a few dwarf plants. The gene-combination of the parental plants must be

two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below.
Assertion (A): Chromosomes inherited from the parents decide the sex of a child.
Reason (R): Y chromosome in a male child is inherited from the father.

Is it possible that a trait gets inherited, but not expressed? Give an example to justify your answer.

In human beings, the probability of getting a male or a female child is 50%. Explain with the help of a flow diagram only.

List any two pairs of visible contrasting characters of garden pea plants used by Mendel for his experiments stating the dominant and recessive characters in each pair.

Mendel crossed pure tall pea plants (TT) with pure short pea plants (tt) and obtained F₁ progeny. When the plants of F₁ progeny were self-pollinated, plants of F2 progeny were obtained.

“Stability of DNA in a species is ensured during sexual reproduction.” Justify the statement.

Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(i) When Mendel crossed pea plants with pure tall and pure short characteristics to produce F₁ progeny, which two observations were made by him in F₁ plants?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
                   RRYY × rryy
      (Round Yellow)   (Wrinkled Green)
Mendel observed 4 types of combinations in F₂ generation. By which method did he obtain F₂ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.

OR

(iii) (B) Justify the statement :
“It is possible that a trait is inherited but may not be expressed.”

In a cross between pure tall pea plants (TT) and pure dwarf pea plants (tt) the offsprings of F$_1$ generation were all tall. When F$_1$ generation was self-crossed, the gene combinations of the offsprings of F$_2$ generation will be :

“In human beings, the sex of a newborn child depends on the father and not the mother.” Justify this statement with the help of a flow diagram.