Whether or not mutations are directed toward the needs of the
organism: Mutation creates new alleles (it is the only source of new
alleles and genetic variation in a population so if there is no mutation
in a population then there will be no variation for selection to act and
genetic drift couldn’t happen)
Mutation is not “random”, but not directed towards the needs of
the organism either
-how do mutations affect fitness? It have little effect on fitness!
-Of those that affect fitness, most are harmful!
-mutation often opposes selection, but also provides raw material
for adaptive evolution
General fitness effects of mutations:
-Other evolutionary mechanisms that cause HWE to change:
-One of non-adaptive evolutionary forces is mutation!
Because it is the only source of new alleles.
-mutation often opposes selection, but also provides raw material for
adaptive evolution. However it is important for selection because
selection require genetic variation and mutation is the only source of
that raw material!
Why most mutations that affect fitness are harmful:
The general effects of mutation on fitness: recall that most
mutations have actually no effect on fitness or very little effect on
fitness, but the ones have effect on fitness, they tend to be harmful,
ex. When there is a certain kind of protein to be copied and there
is mutation, it wont be copied as good as if it was no mutation
because the organisms genes are the product of millions and
million of years of natural selection that are now well adapted to
the environment (ex. Take the laptop and put it apart then try to
put it together again, the odds are that it wont be as good as it was
again!) thus, there are more odds on having something worse
than the previous one with mutations. Effect of gene flow on genetic variation within a population:
The effect of gene flow (migration) on genetic variation: it has a
similar effect to mutation (increase genetic variation)
Effect of gene flow on variation (differences) between populations:
Gene flow (migration) moves alleles between populations
• Like mutation, can introduce new alleles
• Like mutation, often opposes selection (selection-migration
• The effect of gene flow (migration) on genetic variation: it has a
similar effect to mutation EX. a mouse living in the desert has a
pale color that differ from other darker mice.
• Even though mutation is the only way crating new alleles,
migration can introduce those new alleles to a population because
individuals that are migrating bring with them new alleles to that
population. gene flow tends to enhance (increase) the amount of
genetic variation when it is present in a populations (ex. Isolated
populations like a one far in an island where there is no or little
gene flow, they tend to be very poor in genetic variation)
• -Gene flow also tends to operate in opposition to natural selection
because individuals may be coming in from different environment
(like mice from sand are pale in color migrate to another
environment of mice that are much darker color) this results in
some of the individuals in the population being not as well
adaptive to the prevalent conditions ((so this is selection
How various evolutionary forces interact with (reinforce or oppose)
Selection (several kinds)
Which have similar effects on genetic variation within a population?
Mutation and gene flow On differences between populations?
Reasons why not all living things are perfectly adapted to their
• Many factors constrain (limit) selection (see kinds of selection)
– Examples? 1-Dominance status of alleles plays a role here in
that we cant necessarily weed out every copy of a harmful
recessive allele. 2- frequency dependent selection can
maintain phenotypes in a population that have low fitness
simply by being the most common phenotype in a
population. Selection also requires time so in situations
whereas an environment is changing very rapidly then the
population may not be able to evolve quickly enough to
keep up with pace of environmental change. Also selection
requires lots of genetic variation in a population so if the
mutation rate is so low or genetic drift have outweigh the
effects of selection such that there are not a lot genetic
variation, then that constrains the ability of selection to
favour beneficial alleles. Also trade-offs (compromises)
between competing demands (ex. A male fish try to attract
females by having colorful shape and doing smooth dances,
but this increases the chance by which it could be eaten by
• Non-adaptive evolutionary forces often oppose selection(ex.
Harmful mutation, genetic drift migration from other
population…), but without these other evolutionary forces,
especially mutations, adaptive evolution would stop.
Non-random mating and evolution?
• If a population begins mating assortatively for a certain trait,
but all genotypes have the same fitness, what will happen?
– -getotypes AA, Aa, aa – -each genotype mates only with itself
SOLUTION: We have 250 AA 500 Aa 250 aa
The homozygotes will breed with each other in the same genotype and
will get the same homozygote AA and aa
BUT the heterozygotes will be some heterozygotes and homozygotes for
both AA and aa
The offspring from heterozygotes is not goimg to be in HWE because
there will no enough heterozygotes when we sum the total number of
heterozygotes together in the offspring generation population.!
The inbreeding and assortative mating effect is that it increase the
Disassortative have the exact effect, it increase frequencies of
But have the population evolve? No because the allele frequencies have