16-1 Genes and Variation

Chapter 16: Evolution of Populations (16-1)
Darwin did not know how heredity worked
o Source of variation???
o How were characteristics passed from one
generation to another?
Today, genetics, molecular biology, and
evolutionary theory work together to explain how
inheritable variation appears and how natural
selection operates on that variation
Population—collection of individuals of the same
species in a given area. (Share a common gene pool)
Gene pool—combined genetic info of all members
of a population.
Relative frequency—is the number of times an
allele (T) occurs in a gene pool compared with the
number of times other alleles (t) occur.
 Biologists have discovered that there are 2 main
sources of genetic variation: mutations and the
genetic shuffling that results in sexual reproduction.
Chapter 16: Evolution of Populations (16-1)
 Mutations (change in DNA sequence) can affect
an organisms fitness—ability to survive and
reproduce in its environment
Gene Shuffling
 Each gamete contains a different set of genetic
 Crossing over also increases variation
 Slightly different genotypes can dramatically
affect phenotype.
 Sexual reproduction does NOT change the
relative frequency of an allele.
 The number of phenotypes produced for a
given trait depends on how many genes
determine the trait.
 Single-gene trait—only 2 alleles—distinct
 Polygenic traits—2 or more genes—many
phenotypes (averages and extremes), results in
a bell shaped curve.