Page 25 - Genetics_From_Genes_to_Genomes_6th_FULL_Part1

2.1 The Puzzle of Inheritance 17

worth no more than the cost of wool, meat, and skin.” Figure 2.5 Mendel’s garden and microscope. (a) Gregor
Which would it be? According to the meeting’s recorded Mendel’s garden was part of his monastery’s property in Brünn.
minutes, current breeding practices offered no definite an- (b) Mendel used this microscope to examine plant reproductive
swers. In his concluding remarks at this sheep-breeders organs and to pursue his interests in natural history.
meeting, the Abbot Cyril Napp pointed to a possible way (a): © Biophoto Associates/Science Source; (b): © James King-Holmes/Science
Source
out. He proposed that breeders could improve their ability
to predict what traits would appear in the offspring by find-
ing the answers to three basic questions: What is inherited?
How is it inherited? What is the role of chance in heredity?
This quandary is where matters stood in 1843 when
21-year-old Gregor Mendel entered the monastery in
Brünn, presided over by the same Abbot Napp. Although
Mendel was a monk trained in theology, he was not a rank
amateur in science. The province of Moravia, in which
Brünn was located, was a center of learning and scientific
activity. Mendel was able to acquire a copy of Darwin’s On
the Origin of Species shortly after it was translated into
German in 1863. Abbot Napp, recognizing Mendel’s intel-
lectual abilities, sent him to the University of Vienna—all
expenses paid—where he prescribed his own course of
study. Mendel’s choices were an unusual mix: physics,
mathematics, chemistry, botany, paleontology, and plant
physiology. Christian Doppler, discoverer of the Doppler
effect, was one of his teachers. The cross-pollination of
ideas from several disciplines would play a significant role
in Mendel’s discoveries. One year after he returned to
Brünn, he began his series of seminal genetic experiments.
Figure 2.5 shows where Mendel worked and the micro-
scope he used.

(a)
Mendel Devised a New Experimental
Approach

Before Mendel, many misconceptions clouded people’s
thinking about heredity. Two of the prevailing errors were
particularly misleading. The first was that one parent con-
tributes most to an offspring’s inherited features; Nicolaas
Hartsoeker, one of the earliest microscopists, contended in
1694 that it was the male, by way of a fully formed homun-
culus inside the sperm (Fig. 2.6). Another deceptive notion
was the concept of blended inheritance, the idea that pa-
rental traits become mixed and forever changed in the off-
spring, as when blue and yellow pigments merge to green
on a painter’s palette. The theory of blending may have
grown out of a natural tendency for parents to see a combi-
nation of their own traits in their offspring. While blending
could account for children who look like a combination of
their parents, it could not explain obvious differences be-
tween biological brothers and sisters nor the persistence of
variation within extended families.
The experiments Mendel devised would lay these
myths to rest by providing precise, verifiable answers to the
three questions Abbot Napp had raised almost 15 years ear-
lier: What is inherited? How is it inherited? What is the (b)