Doing Science

More about evolution . . .

Evolution 3 Mendel and the Neodarwinian Synthesis 1Nov03

Review: Evolution by natural selection is a consequence of these conditions

  1. potential for rapid reproduction — most organisms can produce more offspring than the environment is capable of supporting
  2. therefore, the availability of resources (food, water, space, light, etc.) will limit the size of the population
  3. where there is heritable variation in traits that influence reproductive success, individuals with those traits should become increasingly predominant in the population.

After Darwin and Wallace, some resistance due to

Populations as the unit of evolution: "variational" evolution (Mayr)

Major points of Darwin's theory

"Origin" published 1859, theory not universally accepted until 1940s.

Problem - Darwin had no idea of the mechanism of inheritance. Consequently

Mendel - worked on peas, published in 1866, practically ignored

Mendelian genetics, rediscovered by Bateson, translated and published in 1902







ploidy - diploid, haploid

homozygous, heterozygous

dominant, recessive

F1, F2

Punnet square



Examples e.g.

Smooth, wrinkled (S, s): cross SS with ss

Cross F1 from the above

Cross tall, smooth (TTSS) with short, wrinkled (ttss)

Cross F1 from the above

Proportions of homozygotes (dominant and recessive) and heterozygotes in a population.

Hardy-Weinberg equation: p2 + 2pq + q2 gives proportions if no evolution is occurring

Factors that can distort the distribution away from Hardy-Weinberg equilbrium

Mendelian concepts at first seen as alternative to natural selection - Bateson et al. not naturalists

T.H. Morgan (1932) possible mechanisms for evolution

Fundamentals worked out late 1920s-early 1930s by Chetverikov, Fisher, Haldane, Wright,

further developed by many others in 1940s - 1950s.

Next: Molecular genetics.


Sources: Evolution (1977). Dobzhansky, Ayala, Stebbins, Valentine.

Mystery of Mysteries (1999) Ruse

What Evolution Is (2001) Mayr

and any good general biology book on Mendelian genetics.