Factors Affecting Gene Frequency
1. Selective Sexual Selection
- Only certain phenotypes get chosen by mates.
The alleles of the chosen ones increase in
frequency. Those alleles not chosen will decrease
in frequency.
Favoured Frequency INCREASE
Unfavoured DECREASE
Example: Peacock fancy feathers in males –
chosen to reproduce. Non-fancy tails – frequency
of alleles will go down.
2. Differential Migration
-If a certain phenotype moves out of an area.
The frequency of those alleles decreases.
Emigrate – Move Out Immigrate – Move In
Ones that moved away: Frequency DECREASE
Ones that stay: Frequency INCREASE
Example: Long necked giraffes on a plain.
3. **** Natural Selection****:
-Certain phenotypes survive and those alleles
increase in frequency. The alleles of
unsuccessful ones decrease.
“Survival Of The Fittest”
Favoured Frequency INCREASE
Unfavoured DECREASE
4. Isolation:”Founder Effect”
-If a small group of individuals is separated
from the main group, they may have a
different frequency of alleles in their gene
pool.
-As the population grows, this frequency may
be much different from the main group.
Frequency CHANGED
5. Random Genetic Drift:
-Occurs in small populations
-Chance mating, or luck can dramatically
change the frequency of alleles in this small
gene pool.
Example: Imagine a bucket of 250 red
marbles and 750 white marbles. A handful of
30 or so marbles would probably not conform
to the 3:1 ratio in the bucket.
In fact, the smaller the sample, the less
accurate might be the final ratio.
-Mutation plus Random Genetic Drift can
change small populations very quickly.
-If the changed group is reunited with the
main population, the two groups may now be
too different for interbreeding.
-We now have 2 species.
Frequency CHANGED
6. Mutations:
- A change to a gene that is inheritable.
- Mutations produce new variations.
-Most mutations are slight, otherwise they are
usually fatal.
-Very few surviving mutants are successful
because populations are already quite well
adapted to their environments.
-Mutations affect the genetic code of DNA
and therefore the proteins being produced,
occasionally the new mutated gene may give
rise to a characteristic/trait that increases
survival of that individual, allowing them to
out-compete the rest of the population.
-Only mutations that affect the sex cells can
cause a population to evolve.
-These mutations will affect the frequency of
alleles.