Independent inheritance

Mendel also crossed plants that differed in two traits at once. A tall plant with round seeds was crossed with a short plant with wrinkled seeds. All the F1 plants were tall with round seeds. But the F2 plants included new mixes: some tall with wrinkled seeds, and some short with round seeds.

So the two traits did not travel together. The reason is that the genes for these two traits sit on different chromosomes. A germ-cell takes one chromosome from each pair, from either parent, so traits can be mixed in new ways.

A small example

NCERT's figure crosses round green seeds (RRyy) with wrinkled yellow seeds (rrYY). The F1 seeds are all round and yellow (RrYy). Its F2 has 556 seeds: 315 round yellow, 108 round green, 101 wrinkled yellow and 32 wrinkled green. That is close to 9 : 3 : 3 : 1 out of 16.

Where marks go

Question 15 of CBSE's 2026-27 Science sample paper crosses VVTT with vvtt pea plants. Part B asks for the share of tall plants with white flowers in F2, for 1 mark. The board's Science marking scheme for 2026-27 accepts 3/16 or 18.75%, from vvTT and vvTt.

Part D, for 2 marks, asks about short plants with white flowers. The answer covers both generations: none in F1, and 1/16 or 6.25% in F2. An answer that gives only F2 leaves out the F1 half. See how step marking works.

About the author

Deepti Sardana

Founder Member & Academic Lead

An IIT alumna (M.Sc., M.Phil.) with over 25 years in teaching, child psychology and learning assessment. As Academic Lead at EduBrahma, she leads the method TRUtesting uses to find where and why a child loses marks.

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