Download Factors Affecting Gene Frequency handout - Mr. Lesiuk

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.