Gregor Mendel’s Experiments With Garden Pea:
I. F2 Progeny
Ben G. Bareja, Nov. 8, 2013

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Gregor Mendel read his “Versuche über Pflanzen-Hybriden” (Experiments in Plant Hybridisation, translated by the Royal Horticultural Society of London) at the Meetings of the Natural History Society of Brünn in 1865. It appeared in print in the following year. Although this paper remained virtually unknown for more than thirty years, it ultimately gave birth to the science of genetics.

Hereunder is my summary reconstruction of some of Mendel’s methodology and part of his observations leading to the Law of Segregation. I would consider these procedures in conducting a similar investigation particularly as a laboratoy exercise. 

Mendel's Methodology

1. Having decided to use garden pea as test plant and having identified the parental purelines to be used in his investigation, Mendel grew a large number of the pea plants in garden plots with a few in pots. The plants consisted of 22 parental types, from which he selected the parents with constant differentiating characters that were later used in his 7 monohybrid crosses.

To keep the plants upright, they were supplied with supports interconnected with strings. In Expt. 7 on stem length, the dwarf plants were carefully transplanted into a separate bed to prevent them from being overshaded by the tall plants.

2. He selected from the lot the most vigorous garden peas and cross pollinated the two parental types having contrasting characteristics, like round or roundish seeds x wrinkled seeds in Experiment 1 (‘smooth’ is also used in place of round or roundish seeds). Seven trials were made totalling 287 fertilizations (23-60 fertilizations per trial) on 70 plants (5-15 plants per trial).

He harvested the mature seeds and started recording their forms (or shape) and the color of the cotyledons (click here to read Parts of a Seed). He entered these observations under the characters of the hybrids (now denoted as F1 or first filial generation; third column in Table E.I-1).  

3. He sowed the mature seeds, producing F1 plants which he allowed to self pollinate (he previously preexperimented and established that garden peas are highly naturally self-pollinated plants).  He evaluated the characters of these plants as to color of seedcoat, form of ripe pod, color of unripe pod, position of flowers on the plant, and length of stem. He entered these observations under the characters of the F1 progeny. 

Observation: Mendel observed that the resulting hybrids (F1) in seven sets of characters tested exhibited only one character of either parent. He also did reciprocal crossings and yielded the same results. 

4. He harvested the mature seeds from the F1 plants and examined these seeds for their form or shape (round or roundish or smooth vs. wrinkled) and the color of the cotyledon (yellow vs. green). These observations were entered under the characters of the F2 progeny. 

5. He planted mature seeds harvested from selfed F1 plants. The resulting F2 plants were allowed to self pollinate and were evaluated for the five other sets of characters under study. 

Why Mendel Used the Garden Pea <<<                      >>> Continue reading: Summary Table of Results

REFERENCE

https://ia600409.us.archive.org/15/items/experimentsinpla00mend/experimentsinpla00mend.pdf, accessed Nov, 2, 2013.

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