Did Mendel "cheat" ?
Mendel's data has led to speculation about the accuracy and
completeness of his reported results, and a perennial
question, Did Mendel Cheat?
(1) Statistical analysis of the
ratios reported in Mendel's 1866 paper suggest they
are "too good:" they conform more closely to the
predicted 3:1 ratio than would be expected given the number of
observations. This has led to suggestions that Mendel
selectively presented only those data that best supported his
hypothesis, or even fabricated the data outright. An
alternative explanation is that Mendel may have observed
ratios close to 3:1 in early counts, and thereafter continued
counting until he felt confident that genuine 3:1 ratios had
been obtained. Researchers nowadays would pre-determine the
number of seeds to be counted, but such statistical
sophistication was not available in the the 1860s.
worked with seven genes, and
Pisum has seven pairs of chromosomes. It is highly improbable that
seven randomly-chosen genes would each occur on a separate
chromosome. Dihybrid crosses involving genes on the same
chromosome would have shown linkage,
which would have been unexplainable by Mendel's rules. [Remember that chromosomes had not
yet been observed in the 1860s]. Therefore, it is concluded, he
must have thrown out some dihybrid results that didn't fit his
In fact, the seven genes map to only four chromosomes, and
only two of these are close enough to show linkage disequilibrium.
As there are (7)(7-1)/2 = 21
possible dihybrid crosses, and Mendel reported results from
only a few of these (not including the linked pair), there is
no basis on which to doubt the accuracy and completeness of
his dihybrid results.