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Polyploidy, meiosis and hybrids can feel like three separate topics in your biology textbook. For E. K. Janaki Ammal they were one question: what happens to chromosomes when you cross two different plants, and what does that mean for a crop? She spent her career answering it, from sugarcane fields in Coimbatore to laboratories in England. This post covers her work, the biology behind it and a short chromosome-counting example of the kind NEET likes to ask.
Who was Janaki Ammal?
According to the John Innes Centre, which named a scholarship after her, Janaki Ammal (1897–1984) "was one of the first women from India to obtain a PhD in Botany (Michigan USA 1931)". She worked at the John Innes Horticultural Institution in England briefly in 1931 and 1935, and for a longer period from 1940 to 1945.
Her early papers show what she cared about. In 1934 she published on polyploidy in Solanum melongena, the brinjal, in the journal Cytologia. Polyploidy, having more than two sets of chromosomes, would run through her work for the next four decades.
What did she do at the Sugarcane Breeding Station?
In 1938 she wrote two letters to Nature from the Sugarcane Breeding Station at Coimbatore. The first, Chromosome Numbers in Sugarcane × Bamboo Hybrids, studied hybrids recently produced at the station by T. S. Venkatraman. She wrote that they gave material for studying how the sugarcane genus Saccharum is related to other grasses, and that this cross spanned a wider gap than earlier crosses of sugarcane with sorghum.
The second, A Saccharum-Zea Cross, dealt with a cross between sugarcane and maize. She opened it by noting that both genera are "distinguished by the readiness with which they cross with related genera". She followed this with papers on intergeneric hybrids of Saccharum in the Journal of Genetics in the early 1940s.
Why did this matter? Sugarcane breeders wanted varieties that grew well in Indian conditions. Crossing cultivated sugarcane with hardy wild relatives is one way to bring in useful traits, but only if you understand what happens to the chromosomes in the hybrid. Counting them, and watching how they pair during meiosis, tells you whether the hybrid will be fertile and stable.
What is the Chromosome Atlas of Cultivated Plants?
At the John Innes Horticultural Institution she worked with its director, C. D. Darlington. The John Innes Centre records that this "led to the publication of the Chromosome Atlas of Cultivated Plants, which she wrote jointly with the then Director". Published in 1945, it brought together chromosome numbers for crop plants, a reference that breeders and cytologists could use to plan crosses.
Worked example: polyploidy and fertility
Imagine a plant species with a basic set of x = 12 chromosomes. This is an illustration, not a specific crop.
A normal diploid has 2n = 2x = 24. Its gametes carry 12.
A tetraploid form (4x) has 48. Its gametes carry 24.
Cross the diploid with the tetraploid. The offspring gets 12 + 24 = 36 chromosomes, three sets: a triploid (3x).
In meiosis, chromosomes pair with their partners. With three copies of each, they cannot be split evenly into two cells, so most gametes get unbalanced sets. Triploids are usually sterile.
That last point is why seedless watermelons and bananas are triploid, and why a breeder needs chromosome counts before planning crosses.
Common mistakes to avoid:
Mixing up n and x. n is the number in a gamete. x is the basic set. In a diploid, n = x. In a tetraploid, n = 2x.
Assuming every polyploid is sterile. Even-numbered polyploids such as tetraploids can pair chromosomes normally. Odd-numbered ones are the problem.
Forgetting meiosis is the cause. The sterility comes from pairing at meiosis, not from mitosis. Our guide to the cell cycle, mitosis and meiosis walks through the stages.
When the stages of meiosis blur together, it often helps to go back to the one idea you are missing, such as what a bivalent is. The Fermi Concept Library covers every concept in biology with its own lesson, so you can fix that gap before trying more questions.
What did she work on after returning to India?
Back in India, she kept publishing on chromosomes and plants. In 1959 she wrote about the Central Botanical Laboratory in Nelumbo, the journal of the Botanical Survey of India. Her later papers in the Proceedings of the Indian Academy of Sciences included work on tetraploidy and alkaloid content in Datura metel, which linked chromosome doubling to the chemistry of a medicinal plant.
The Government of India's Padma Awards notification for 1977 lists "Dr (Miss) Edavaleth Kakkat Janaki Ammal, Centre of Advanced Studies in Botany, University Botanical Laboratory, University of Madras" among that year's Padma Shri recipients.
What can a student learn from how Janaki Ammal worked?
Follow one question across many plants. Brinjal, sugarcane, maize, Datura: the organisms changed, the question about chromosomes did not.
Count before you conclude. Her letters are full of numbers. A claim about a hybrid starts with how many chromosomes it has.
Connect the lab to the field. Chromosome counts mattered because farmers needed better crops.
For more on how heredity and variation lead to new species, see our post on evolution for NEET.
Try it now: a plant with 2n = 20 is crossed with its tetraploid form. Write down the chromosome number of the hybrid and say whether you expect it to be fertile.
