Study the given table and answer the following questions: Parents F_1 F_2 --- --- --- A pea plant with red flowers was crossed with a pea plant with white flowers. 30 seeds were sown and all bore plants with red flowers. 44 seeds were sown, 33 plants bore red flowers and 11 plants bore white flowers. (a) Depict the information given in the table in the form of a cross. (b) Deduce the F_2 phenotypic ratio/F_2 ratio showing external look as well as genotypic/genetic makeup, ratio.

ScienceCBSE Class 10 · Board exam 2026, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2026: question 14

Set in the CBSE Class 10 board exam of 2026, paper 31/4/1, section A, question 14, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q14 · 3 marks · Short answerCompetency-basedHeredity

Study the given table and answer the following questions:

Parents	$F_{1}$	$F_{2}$
A pea plant with red flowers was crossed with a pea plant with white flowers.	30 seeds were sown and all bore plants with red flowers.	44 seeds were sown, 33 plants bore red flowers and 11 plants bore white flowers.

(a)
Depict the information given in the table in the form of a cross.
0 marks
(b)
Deduce the $F_{2}$ phenotypic ratio/ $F_{2}$ ratio showing external look as well as genotypic/genetic makeup, ratio.
0 marks

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/4/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Since all F $_{1}$ plants are red, decide which colour is dominant.

Hint 2

Cross the F $_{1}$ with itself and fill a 2×2 Punnett square.

Hint 3

Simplify 33 : 11, then count RR, Rr and rr in the square.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(a) Let R = dominant allele for red flowers and r = recessive allele for white flowers.
Parents: RR (red) × rr (white)
½ mark
Gametes: R and r.
F $_{1}$ : Rr, all plants red. This agrees with the table: all 30 F $_{1}$ plants bore red flowers.
½ mark
Selfing of F $_{1}$ : Rr × Rr.
Gametes from each parent: R and r.
½ mark
F $_{2}$ (checkerboard):
♂ \ ♀ R r
R RR (red) Rr (red)
r Rr (red) rr (white)
½ mark
(b) Phenotypic ratio: Red : White = 33 : 11 = 3 : 1.
½ mark
Genotypic ratio: RR : Rr : rr = 1 : 2 : 1.
½ mark

♂ \ ♀	R	r
R	RR (red)	Rr (red)
r	Rr (red)	rr (white)

Answer: Cross: RR × rr → F $_{1}$ Rr (all red); Rr × Rr → F $_{2}$ RR, Rr, Rr, rr. Phenotypic ratio 3 red : 1 white (33 : 11); genotypic ratio 1 RR : 2 Rr : 1 rr.

Where the marks are

Writes the parents as RR × rr (½ mark)
Shows the gametes and F $_{1}$ as Rr, all red (½ mark)
Shows F $_{1}$ selfing, Rr × Rr, with its gametes (½ mark)
Gives the F $_{2}$ checkerboard or offspring RR, Rr, Rr, rr (½ mark)
States the phenotypic ratio 3 : 1 (½ mark)
States the genotypic ratio 1 : 2 : 1 (½ mark)

Revise the chapter

Chapter: Heredity (notes, formulas, where marks are lost and every past question)
Topic: Mendel's Experiments and Monohybrid Cross

Practise this chapterBoard-style questions from Heredity, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 31/4/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 10 Science 2026: question 14

Hints

Step-by-step solution

Revise the chapter

More questions from Heredity