Heredity and Evolution — Class 10 Science PYQs

Which one of the following statements is NOT true ?

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 :

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 :

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

Q. Nos. 17 to 20 are Assertion - Reason based questions :
These questions consist of two statements - Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below :
(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 the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Assertion (A) : Human female has a perfect pair of sex chromosome.

Reason (R) : Sex chromosome contributed by the human male in the zygote decides the sex of a child.

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 ${\text{F}}_1$ progeny, which two observations were made by him in ${\text{F}}_1$ plants ?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
$\text{RRYY}\times \text{rryy}$
(Round Yellow) (Wrinkled Green)
Mendel observed 4 types of combinations in ${\text{F}}_2$ generation. By which method did he obtain ${\text{F}}_2$ 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."

Q. Nos. 37-39 are source-based/case-based questions with 2 to 3 short sub-parts. Internal choice is provided in one of these sub-parts :

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 ${\text{F}}_1$ progeny, which two observations were made by him in ${\text{F}}_1$ plants ?
(ii) Write one difference between dominant and recessive trait.
(iii) (A) In a cross with two pairs of contrasting characters
$\text{RRYY}\times \text{rryy}$
(Round Yellow) (Wrinkled Green)
Mendel observed 4 types of combinations in ${\text{F}}_2$ generation. By which method did he obtain ${\text{F}}_2$ 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."