Population - a group of organisms of the same species living
in the same area
members within a population are more likely to mate with one another
than with members of other populations
genes flow among members of a population
Five characteristics of populations that can affect the process (or
rate) of change (evolution)
size of population
genetic drift (evolution due to chance events alone) can have a
much greater effect on small populations than large populations
mating pattern
selection pressure
rate of migration
gene flow - the spread of genetic information
from one population to another by immigration and emigration
rate of mutation
The two characteristics that we modeled in lab were:
size of population (genetic drift in a small population)
selection pressure (certain phenotype results in death or sterility)
Darwinian evolution - in order to occur the following sequence
of events must be present
production of an overabundance of offspring
some genetic-based variability among the offspring
differences in survival among the offspring
differences in reproduction among the survivors
increased frequency of adaptive characteristics in the next generation
Be able to figure out genotype, phenotype, & allele frequencies
(for example, for the population of 3AA, 2Aa, 3aa)
allele frequency = gene pool
genotype frequency - 3/8 AA; 2/8 Aa; 3/8 aa (fraction of population
for each genotype)
phenotype frequency - 5/8 with yellow teeth; 3/8 with green
teeth (fraction of population for each phenotype)
allele frequency - 8/16 A; 8/16 a (fraction of alleles of each
type of allele)
Simulation of a model (stable) population
in a stable population evolution is not occurring
the genotype and phenotype frequencies may change, but the allele frequency
remains constant
this situation does not occur in the real world
A population whose gene pool
remains the same from one generation to the next is said to be in Hardy-Weinberg
equilibrium
Variation: A Selection Model
recessive alleles “hide” in a population in heterozygous individuals
therefore, it is very difficult to remove recessive alleles from a
population
dominant alleles cannot “hide” - the phenotype is always shown
dominant alleles are much easier than recessive alleles to remove from
a population
selection acts on the phenotype, not directly on the genotype
Variation: a Small Population
genetic drift - evolution (change) caused by chance alone
small populations are more subject to genetic drift than large populations
it is difficult to make predictions about what future generations of
a small population will look like, due to genetic drift
Computer Models
Hardy-Weinberg equilibrium - the graph appears as a straight line (since
the allele frequency remains constant)
If you know the frequency of one allele (e.g. A), you can find the
frequency of the other allele (e.g. a) by subtracting the frequency from
one (1-freq. A = freq. a)