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Lecture 3
Department
Biological SciencesCourse Code
BIO SCI 94Professor
Robin BushLecture
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Bio 94 Lec 3
”Survival of the Fittest"
~Most scientists do not use the phrase "survival of the fittest" to refer to natural
selection, and you should not use it either.
The problem?
~Fitness is determined by the relative proportion of genes an individual
contributes to the next generation, as compared to the proportion contributed by
other individuals in the population.
~“urvival is oly iportat i that you have to live log eough to reproduce.
You can survive to a very old age, but if you don't have any children, your fitness
is zero.
Question:
Cotton-topped tamarins are small primates with tufts of long white hair on their
heads. While studying these creatures, you notice that males with longer hair get
more opportunities to mate and father more offspring. To test the hypothesis
that having longer hair is adaptive in these males, you should?
determine if hair length is heritable
Biologists often want to test whether
– natural selection is acting on a particular gene
– nonrandom mating is occurring
– one of the other evolutionary mechanisms is at work
~In addressing questions like these, the Hardy– Weinberg principle functions as a
null hypothesis
~When genotype frequencies do not conform to Hardy–Weinberg proportions,
evolution or nonrandom mating is occurring in that population
~ Hardy and Weinberg imagined that all of the gametes produced in each
generation go into a single group called a gene pool and then combine randomly.
~Their calculations predict the genotypes of the offspring that the population
would produce, as well as the frequency of each genotype.
~When alleles are transmitted via meiosis, and gametes combine randomly,
alleles frequencies do not change.
~For evolution to occur (for allele frequencies to change), some other factor or
factors must come into play.
~Random mating is the null hypothesis.
There are four mechanisms that shift allele frequencies in populations:
1. Natural selection increases the frequency of those alleles that contribute to
reproductive success in a particular environment.
2. Genetic drift causes allele frequencies to change randomly
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