Experiment 1: Mendel and Apomixis

Mendel came to some general rules:

  • Many traits are determined by pairs of factors; in many cases, one of these factors is "recessive" to the other, which is termed the "dominant" factor.
  • An organism inherits one factor from its maternal parent and one from its paternal parent.
  • Factors segregate independently of one another during the formation of gametes.  A particular gamete (sperm or egg) has an equal probability of carrying either the organism's maternal or paternal form of the factor.
  • Once "reunited" upon fertilization, the new organism has two factors that remain distinct, there is no "blending" of factors.

After working with peas, and on the advice of the famous professor Karl von Nägel, Mendel turned to another plant, the hawkweed (genus: Heiracium).   The goal was to determine how general these rules were. 

Unfortunately, hawkweed was bad choice.  In contrast to peas, and most other plants, hawkweed reproduces asexually, through a process known as apomixis.

During apomixis, the new organism (the embryo) is derived solely from the mother by the process of parthenogenesis (virgin birth).  Fertilization does occur, but it influences only the extra-embryonic part of the seed - the endosperm. 

Mendel's conclusions do not apply to such an organism.  In 1869 Mendel published a report that hinted that the results he obtained from hawkweed were quite different from those obtained using peas.

This undermined his confidence in the generality of his conclusions.

Experiment 1: How do apomixic plants differ from conventional plants?

You start a series of experiments on hawkweed. You have established two pure-breeding lines - one produces bright orange flowers and is tall, the other produces dusky red flowers and is short.   Characterize the pattern of inheritance of these traits using javaGenetics™  and describe how they differ from the behavior of the traits studied by Mendel in the pea.

Rediscovering Mendel

The reemergence of Mendel's ideas began in earnest in March 1900.

Hugo deVries published a paper entitled "Das Spaltungsgesetz der Bastarde" (The Law of Splitting of Hybrids). It was followed within months by similar observations from Carl Correns and Erick von Tshermak-Seysenegg.  

Once rediscovered, Mendel's work became the focus of an explosion of scientific study in the early part of the 20th century.

Much of this work involved the clarification of ideas, terms, genetic "rules" and how apparent exceptions to these rules could be understood within a coherent conceptual framework.

Use Wikipedia to look up concepts | revised 10-Dec-2005