One of world’s best ideas: the distinction between genotype and phenotype

One of the most important ideas ever is the distinction between genotype and phenotype – between our genes and the traits they influence. It seems obvious to us now, but scarcely more than 100 years ago it wasn’t, which led to a lot of confusion.

The scientist who really clarified the distinction between genotype and phenotype (and who, along with the word gene, coined these terms), was Wilhlem Johannsen. I recently wrote about Johannsen for Pacific Standard, in the context of the recent discovery of the molecular basis of a European blond allele. Here I want to show why Johannsen’s key insight dispelled so much confusion.

Johannsen summed up his views in a 1911 paper, “The Genotype Conception of Heredity.” He starts out by saying that scientists have been confused because they are thinking about apparent heredity, or the “transmission-conception” of heredity. This transmission conception, which had been around since Hippocrates and Aristotle, was that “the personal qualities of any individual organism are the true heritable elements of traits!” Continue reading “One of world’s best ideas: the distinction between genotype and phenotype”

Even Boltzmann had trouble with probability

Boltzmann was one of the genius founders of statistical thermodynamics, and yet the subtleties of probability tripped him up:

From “Compendium of the foundations of classical statistical physics” by Jos Uffink:

He introduced the probability distribution as follows:

“Let (v)dv be the sum of all the instants of time during which the velocity of a disc in the course of a very long time lies between v and v + dv, and let N be the number of discs which on average are located in a unit surface area, then

N ϕ(v)dv

is the number of discs per unit surface whose velocities lie between v and v + dv” Continue reading “Even Boltzmann had trouble with probability”