3.4 Inheritance

Making quantitative measurements with replicates to ensure reliability. Mendel’s genetic crosses with pea plants generated numerical data.

Gregor Mendel, the “Father of Genetics”, made his discoveries on inheritance by using the garden pea, Pisum sativum. Mendel’s experiments and data collection over eight years formed the foundation of theoretical genetics and were able to be used in diagnosing and explaining genetic diseases at the turn of he 20th-century.  Just as important as his discoveries, though, was his meticulous following of the scientific methods, illustrating perfectly that replicates in quantitative experiments allow for greater reliability in the conclusions.

The seven traits Mendel studied (Griffiths et al.)

Mendel worked with the seven traits outlined above and bred them for two years to establish pure, or homozygous, breeding strains. He then pollinated the parental flowers that showed variation in the trait – for example, crossing purple flowers with white flowers.  This produced in the F1 generation 100% purple flowers.  When these flowers were self-pollinated, Mendel noticed a curious relationship in the F2 offspring: a ratio of almost exactly 3:1 in the phenotype.

Screen Shot 2016-05-02 at 3.24.45 PM
The data of the F2 ratio from Mendel’s experiments, a total of over   18, 000 breeding experiments. (Griffiths et al.)

On the basis of this data, Mendel was able to draw key conclusions about the nature of inheritance.  These were:

  1. The existence of what we now know as genes.
  2. That these genes come in pairs
  3. Gene pairs segregate during the production of gametes
  4. Each gamete thus only contains one gene of a pair.
  5. Fertilisation is random

These statements were able to be tested by a new round of experiments, because they were based on quantitative data, had significant repetition and suggested certain patterns in inheritance.  His subsequent experiments provided confirmation of his analysis.  Not bad, considering the structure of DNA wouldn’t be determined for another century!

Mendel also did some interesting work on dihybrids, but that’s for a later topic!


Griffiths AJF, Miller JH, Suzuki DT, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Mendel’s experiments. Web. May 2, 2016.

Miko, I. Gregor Mendel and the principles of inheritance. Nature Education 1(1):134. 2008. Web. May 2, 2016.


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