The factors affecting the frequency of alleles

1.

2. The factors affecting the frequency of alleles

3. Learning objective

•call factors affecting the frequency of
alleles

4. Success criteria

• Write at least eight ideas. For example they can
enumerate five factors and give only three
examples or they can enumerate four factors
with an example for each factor.
• Know factors that influence alleles’ frequency.

5. Terminology

• Gene pool
• Genetic drift: Founder Effect, Bottleneck Effect
• Gene Flow (migration): immigration/emigration
• Nonrandom Mating
• Mutation
• Changing Populations: Hardy-Weinberg Equilibrium
Theory

6. Genetic drift

• Genetic drift is a change in allele frequency that
occurs by chance, because only some of the
organisms of each generation reproduce.
• It is most noticeable when a small number of
individuals are separated from the rest of a large
population.
• reduces genetic variation
• bottleneck effect, founders effect

7. Genetic drift

8. Genetic drift

9. Founder effect

• The founder effect is a phenomena that occurs when a small group of
individuals becomes isolated from a larger population.
• A few individuals from a larger population colonize a new habitat
• Produce a new colony.

10. Founder effect

11. Bottleneck effect

• Genetic drift can cause big losses of genetic variation for small
populations.
• reduces genetic variation

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13. An example of a bottleneck

• Northern elephant seals have reduced
genetic variation probably because of a
population bottleneck humans inflicted on
them in the 1890s. Hunting reduced their
population size to as few as 20 individuals at
the end of the 19th century. Their population
has since rebounded to over 30,000 — but
their genes still carry the marks of this
bottleneck: they have much less genetic
variation than a population of southern
elephant seals that was not so intensely
hunted.

14.

15. Gene flow

• In population genetics, gene flow (also known as gene migration) is the transfer
of genetic variation from one population to another.
• migration — is any movement of individuals, and/or the genetic material they
carry, from one population to another.
• tends to reduces differences between population

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18. Immigration and Emigration

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20. Nonrandom Mating

• Nonrandom mating occurs when the probability that two individuals
in a population will mate is not the same for all possible pairs of
individuals.
• When the probability is the same, then individuals are just as likely to
mate with distant relatives as with close relatives -- this is random
mating.
• Living organisms) try to choose mates that will maximize their on
fitness.

21. Nonrandom Mating

22. Mutation

• a new mutation will be
transmitted in the gametes
changing the gene pool of a
population by substituting one
allele for another.
• Change is genetic material and are
the raw material for evolutionary
change.
• Point mutation can introduce a
new allele into a population.

23.

24. Hardy – Weinberg equilibrium

• states that allele and genotype frequencies in a population will
remain constant from generation to generation in the absence of
other evolutionary influences.
•States that the allele frequency for
dominant and recessive alleles remains
the same in a population for many
generations

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27. Solve problem

28. Success criteria

• Write at least eight ideas. For example they can
enumerate five factors and give only three
examples or they can enumerate four factors
with an example for each factor.
• Know factors that influence alleles’ frequency.