Transcript Population Genetics

Aim: What are population genetics and how do they affect
evolution?
I. Population Genetics – Genetics today is concerned with
inheritance in large groups of sexually reproducing animals.
The study of these organisms as a reproducing group is known
as population genetics.
A. Key Terms
1. Species – a group of organisms that have many
genetic characteristics in common and can interbreed.
2. Population – members of a species that
inhabit a specific geographic area.
3. Gene Pool – the sum total of all the genes collectively
present within a given population
B. What causes changes in gene pools?
1. Recombination – during meiosis, chromosome
pairs separate and then recombine during fertilization
to form new combinations of chromosomes in the
zygote.
2. Crossing Over – During meiosis, portions of
chromosomes exchange places to produce new
combinations of genes in the chromatids.
3. Mutations
C. Environmental Changes can change a gene pool.
1. Gene frequency – a number indicating the
ratio of a gene to its other alleles in a gene
pool.
a. Allele – the alternative genes for a trait.
Example, in the case of the height trait, the
genes for tallness and shortness.
2. If an organism possesses a gene that helps it
survive in its environment, that gene frequency will
increase, and vice versa.
3. Changing environments promote changes in the
composition of gene pools.
D. Adaptive Radiation – the divergence of a single
population into groups having differing traits.
1. With sufficient divergence, a
new species may be formed, a
process called speciation.
E. Geographic Isolation – isolation of populations by
geographic barriers.
What are some examples of geographic barriers?
1. Mountains, canyons, rivers, highways, climate
and even other organisms can serve as barriers for
various kinds of plants and animals.
2. When a population becomes divided by a barrier,
interbreeding cannot occur. Genes will not flow between
them and their gene pools may diverge.
F. Reproductive Isolation
1. Due to geographic isolation, the two populations
become increasingly different. This may lead to:
a. Differences in reproductive organs
b. Differing courtship patterns
c. Differences in chromosomes
2. When organisms can no longer interbreed due to
the above differences, they are said to be
reproductively isolated.
G. Geographic Distribution – Depending on where
organisms originated, affects how they evolved.
Continental Drift.