NAME: KEY
5
Part III. Short Answer/Problems. Be concise and to the point, short focused answers are
better than long rambling ones. Show your work for partial credit.
21. (3 pts.) Darwin developed his theory of Evolution by Natural Selection over the course of
many years of careful observation and study. List three (3) scientific areas / theories /
observations that contributed to his revelation in the following passage:
“… it at once struck me that under these circumstances favourable variations would tend
to be preserved and unfavourable ones to be destroyed.”
September 28, 1838
There are a lot of possibilities for this one including the observations he made on te
effect of selection in domesticated animals, the observation of variation among island
populations in the Galapagos, the emerging understanding of the age of the earth from
the field of geology, the law of succession, Malthus’s work on population growth, etc.
22. (8 pts.) By the early 1940’s the unification of evolutionary biology that we now refer to as the
“Modern Synthesis” had been completed. The unification of the field was facilitated by a large
number of researchers in the fields of genetics, systematics, and paleontology. One of the
major outcomes of the “Modern Synthesis” was a clear description of the evolutionary forces
acting on natural populations. Below, list four (4) forces affecting the evolution of natural
populations. (1 pt each)
1) SELECTION
2) MUTATION
3) RANDOM GENETIC DRIFT
4) MIGRATION
These forces influence the patterns of genetic variation in natural populations. Briefly compare
and contrast the way that each of these forces influences genetic diversity. (1 pt each)
These forces all influence the patterns and amounts of genetic variation in natural
populations in different ways. Mutation increases genetic variation. Random genetic
drift reduces genetic variation. Selection typically reduces variation. However, some
forms of selection can maintain genetic variation. For example, frequency dependent or
overdominant (heterozygote advantage) selection can maintain genetic variation.
Migration can either increase or decrease genetic variation depending on how it
influences gene frequencies. In the extreme case when novel alleles are being
introduces from another population, migration can rapidly change gene frequencies and
increase variation. However, if gene frequencies are changed so that the population is
moved farther from equal frequencies of alleles (p=0.5, q=0.5) migration will tend to
reduce heterozygosity and reduce genetic variation.