Monk learns secrets of heredity from pea plants, Science News Online (12/18/99)

 Monk learns secrets of heredity from pea plants

 By J. Travis

 BRÜNN, Austria, March 1865-It may be the most interesting research on peas 
since noted Danish science writer Hans Christian Andersen reported that the 
legume causes insomnia among princesses. An Austrian monk has spent the past 
decade growing pea hybrids and religiously recording how certain physical 
traits-pod color, seed shape, and plant height, among others-pass from one 
generation to the next. He now claims to have found that a few simple rules 
govern the process.

 Johann Gregor Mendel of St. Thomas Monastery, who described his results at 
this and last month's meetings of the Natural Sciences Society in Brunn, says 
that physical traits in other plants, as well as animals, may follow similar 
principles in their inheritance. "I am convinced that it will not be long 
before the whole world acknowledges the results of my work," he told Science 
News.

 In his experiments, Mendel examined more than 28,000 pea plants, noting seven 
traits that each come in two easily distinguishable forms. For example, pods of 
a pea plant are either green or yellow; their seeds, round or wrinkled; and 
their height, tall or dwarfed.

 To create his hybrids, Mendel brushed the pollen of one pea plant onto the 
pistils of another. He started by crossbreeding strains that had already proved 
constant for one form of a trait with strains consistently showing the other 
form. For example, he crossed a tall strain with one whose stems were always 
short.

 Surprisingly, in light of current hybridization theories, the resulting plants 
did not show blending of any of the seven physical traits. The crosses between 
tall and dwarf strains did not produce medium-size plants. Instead, they 
invariably resulted in tall plants. "Transitional forms were not observed in 
any experiment," Mendel says.

 The monk, who is also a meteorologist, dubs the form of each trait prevailing 
in the hybrids-green pods, round peas, long stems-"dominant" and the trait that 
disappears, "recessive." He speculates that through their eggs or pollen, the 
parents of a hybrid contribute to their offspring an element representing the 
dominant or recessive trait but not both. Therefore, when pollen and eggs join 
to form a seed, various combinations of the elements can result, but the 
presence of a dominant trait will always mask the recessive one.

 In further experiments, Mendel allowed his hybrid pea plants to 
self-pollinate. He discovered that the recessive forms of each trait reappeared 
in a significant fraction of the offspring, demonstrating that the hybrid 
somehow continues to carry the recessive element in at least some of its seeds. 
In one experiment, notes Mendel, hybrids having green pods gave rise to 428 
plants with green pods and 152 with yellow ones. Mendel documented similar 
ratios for all the traits he monitored. He concluded that among the offspring, 
when two hybrid plants are crossed, the dominant form of a trait generally 
outnumbers the recessive form 3 to 1.

 Moreover, Mendel studied whether choice of one trait, say pod color, 
influences how often the form of a second trait, such as seed shape, passes 
from one generation to another. The data clearly indicate that each trait is 
inherited independently of the other ones, he contends.

 Leading botanists contacted by Science News were either unaware of Mendel's 
data or openly skeptical about his conclusions. The work on peas is intriguing 
but "incomplete," says German botanist Carl Wilhelm von Nageli. To confirm its 
general applicability, von Nageli argues, Mendel should conduct similar 
hybridization experiments with other plants, such as hawkweed.