On this page
Artificial hybridisation takes up only two paragraphs of NCERT, but it links three things you study separately: flower structure, pollination and Mendel's genetics. Questions ask why a step is needed, when it can be skipped, and what would go wrong without it. This post explains each step, shows how Mendel did it with peas, and works through a check that tells a breeder whether a cross actually succeeded.
Where is this in the syllabus?
The method is described in NCERT's Class 12 Biology Chapter 1, Sexual Reproduction in Flowering Plants (2026-27 reprint), at the end of the pollination section, just after pollen-pistil interaction. The NEET (UG) 2026 syllabus lists pollination, outbreeding devices and pollen-pistil interaction in that chapter. The CBSE Biology curriculum for 2026-27 adds a practical: "Controlled pollination - emasculation, tagging and bagging". Check your own year's documents.
Why does a breeder need artificial hybridisation?
NCERT puts it simply: a breeder wants to cross different species, and often genera, to combine desirable characters into commercially "superior" varieties. For that, two things must be true: only the chosen pollen reaches the stigma, and the stigma is protected from unwanted pollen. Emasculation and bagging achieve those two goals.
What are the steps for a bisexual flower?
Emasculate. Remove the anthers from the flower bud with forceps before they dehisce, that is, before they split and release pollen. Doing it at the bud stage is the whole point: once anthers open, self-pollen may already be on the stigma.
Bag. Cover the emasculated flower with a bag of suitable size, generally butter paper, so no stray pollen arrives by wind or insects.
Pollinate. When the stigma becomes receptive, dust it with mature pollen collected from the anthers of the chosen male parent.
Rebag. Cover the flower again and let the fruit develop.
Tag. The CBSE practical list adds tagging: labelling the bagged flower so the cross it carries is recorded.
What changes for unisexual flowers?
If the female parent produces unisexual flowers, there is no need for emasculation, since a female flower has no anthers. NCERT's version: bag the female flower buds before the flowers open, pollinate with the desired pollen when the stigma becomes receptive, then rebag.
So for maize, a monoecious plant, the breeder bags the female flowers but does not emasculate. For papaya, a dioecious plant, a female plant's flowers likewise need bagging only. Our post on outbreeding devices and pollination explains monoecy and dioecy in detail.
How did Mendel do it?
Mendel chose the garden pea partly because foreign pollen cannot easily get into its flowers. In the English translation of his 1865 paper, Experiments in Plant Hybridization, he explains that the anthers burst within the bud, so the stigma is covered with pollen even before the flower opens. That is why, for a cross, "the bud is opened before it is perfectly developed, the keel is removed, and each stamen carefully extracted by means of forceps", after which the stigma could be dusted with the other variety's pollen. He called the process "somewhat elaborate" but said it "nearly always succeeds".
He also worried about contamination. He noted that a pea beetle, Bruchus pisi, opens the keel when laying eggs and can carry pollen. Even so, among more than 10,000 plants he examined carefully, there were only "a very few cases" of indubitable false impregnation, his term for contamination.
Worked example: did the cross work?
Mendel noted something useful: seed shape and the colour of the seed's albumen, as the translation calls it, show the hybrid's form immediately after the cross, in the same season. A breeder can use this as a check.
Suppose a breeder crosses a green-seeded pea (yy) as the female with pollen from a yellow-seeded pea (YY). Yellow is dominant.
If the cross worked, each seed is Yy and yellow.
If self-pollen got in, because the anthers were removed too late or the bag leaked, that seed is yy and green.
The breeder harvests 236 seeds from the crossed flowers. These are sample numbers for practice. 227 are yellow and 9 are green.
Fraction from accidental selfing: 9/236 ≈ 0.038, or about 3.8 per cent.
The 227 yellow seeds are the true hybrids to sow.
Notice the choice of parents. If the female had been the yellow YY plant, selfed seeds would be YY and yellow, identical in look to the Yy hybrids, and the mistake would stay hidden. Putting the recessive form on the female side makes contamination visible.
Which mistakes cost the most marks?
Emasculating after the anthers dehisce. By then self-pollination may have happened.
Saying unisexual flowers need emasculation. They need bagging only.
Removing the bag before the stigma is receptive and never rebagging after pollination.
Confusing emasculation with removing petals. It means removing anthers.
Forgetting why: the purpose is that only the desired pollen reaches the stigma.
A practice routine
Day 1: Write the five steps from memory and add one sentence of reason to each.
Day 2: For pea, maize, papaya and a cucurbit you choose, decide which steps apply and why.
Day 3: Make up a cross with a dominant and a recessive seed trait. Decide which parent should be the female so contamination shows, and calculate the selfing fraction for a sample count.
Day 4: If your school runs the CBSE practical, do the exercise and note where the timing was hard.
For the rest of the chapter, from pollen to double fertilisation, see our post on reproduction in flowering plants. If a step in flower structure is unclear, the Fermi Concept Library covers every concept in biology with its own lesson.
Try this now: explain in two sentences why a breeder crossing two maize varieties bags the female flowers but does not emasculate them.
