Download PGS: 454 – 458

Unit 3: Evolution
Evolution of Populations (3.1) – Part 1
I.
Evolution - the process through which a population’s traits change over time.
A. Types of Evolution:
1. Microevolution- evolution or change on a small scale.
a. This term usually refers to changes within a population of a species.
b. Microevolution can eventually lead to macroevolution.
2. Macroevolution- evolution or change on a large scale.
a. This term refers to the evolution of a new species of organism from a pre-existing species
of organism.
B. Remember: Change over time is referred to as evolution. Evolution is a scientific law… the environment
changes from minute to minute, hour to hour, day to day; just as a genome may. Please do not confuse
this “change over time” with the belief of creationism. These are two different concepts that are confused
with each other because of misconceptions of the definition.
II.
Population Genetics
A. The science that studies the change in distribution of traits within a species population. (A.K.A. a Gene
pool.)
1. Species
a. Organisms that are so genetically similar that they have the potential to breed and
produce organisms that are:
i.
Viable (living).
ii.
Fertile (able to reproduce eventually themselves).
2. A population is defined by four criteria:
a. Same species of organism.
b. Located in the same location.
c. At the same time.
d. And showing signs of reproduction. (Offspring are present within the group.)
3. Geographic range - the geographical area within which a species can be found.
a. Organisms that are common (i.e. grey squirrels or humans) may have several populations
that cover a wide range.
b. Some species like humans are global in range.
i. Humans have millions of different populations, such as the population of
Montgomery, Huntsville, Mobile, or the population of Birmingham.
c. Different populations may or may not interact. It just depends on the species and if any
geographic barriers (i.e. large mountains or large bodies of water) interfere with their
ability to interact.
B. Populations evolve; not individuals. (You do not evolve; you get older, larger, and smarter!)
1. This is because we “are” what we “are” because of the genes that we inherit from our parents.
You cannot change the DNA you were given from your biological parents but genetic
mutations can occur randomly over your lifetime.
a. Mutations are random changes that occur in an organism’s DNA. Some mutations help
individuals survive in their environment and reproduce. Some mutations do not help an
organism survive. Other mutations have no effect.
b. If a mutation (change) occurs in the DNA of sex cells (gametes) of the parent(s), then
those changes could be inherited by the offspring (next generation).
c. Individuals can be positively or negatively affected as a result of the traits that they
inherit; as well as, by the mutations that they acquire during their life.
2. Allele frequency- how many alleles are present at that time, within the population.
a. Fixed - there is no change in frequency; no evolution is present. (A state of equilibrium.)
b. Evolving - frequency is changing; evolution is occurring. (A state of change over time.)
3. An allele is a version of a gene, such as blue or brown for eye color.
a. There are always at least 2 alleles for a trait, sometimes several.