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Chapter 16-1:
Genes and Variation
Darwin’s Handicap
Although Mendel’s work on genetics was published in Darwin’s lifetime, there
were two big gaps in his thinking
1. Darwin had no idea how _________________________________ pass
from one generation to the next
2. Although variation in heritable traits was central to Darwin’s theory, he
had no idea __________________________________________________
Mendel meets Darwin
It wasn’t until the 1930’s that Mendel’s ideas of genes fused with Darwin’s ideas
of evolution
Changes in genes produce ________________________________ on which
_______________________________ can operate
Gene Pools
Genetic variation is studied in populations
– A group of individuals of the _____________________ species that
________________________________
A gene pool consists of all the ___________________, including all the
different alleles, that are present in a _________________________
Relative Frequency
The relative frequency of an allele is the number of times that the allele occurs in
a ________________, compared with the number of times other alleles for the
same gene occur
 In genetic terms, evolution is any change in the ________________________
of alleles in a population
Genetic Variation
The two main sources of genetic variation are
_____________________________: any change in DNA
the ______________________ that results from sexual reproduction,
including ________________________________
Single Gene vs. Polygenic Traits
The number of phenotypes produced for a given trait depends on how many genes
control the trait
– ____________________________ – phenotype that is controlled by a
single gene that has two alleles
Frequencies are represented by a bar graph
–
_______________________________ – phenotype that are controlled by
two or more genes, often involving two or more alleles
Frequencies are represented in a line graph (bell curve)
Chapter 16-2:
Evolution as Genetic Change
Genetic Views of Evolution
 Evolutionary fitness is an organism’s success in ________________________
_______________________________________________________________

Evolutionary adaptations are any genetically controlled _________________,
____________________, or ______________________________ trait that
increases an individual’s ability to pass on its genes
Natural Selection and Genetics
 Natural selection never acts on a gene
– It acts on the _______________ as a whole (the entire collection of genes)
–
It can only affect which individuals ______________________ and
___________________________ and which do not
Natural Selection on Single Gene Traits
 Natural selection on single gene traits can lead to changes in
___________________________________ and thus to evolution
– Peppered moths during industrial revolution
Natural Selection on Polygenic Traits
 Natural selection can affect the distributions of phenotypes in any of three
ways:
–
–
–
Directional Selection
 When individuals are ___________________ of the cure have higher fitness
than individuals in the middle or at the other end
Stabilizing Selection
 When individuals ___________________________ of the curve have higher
fitness than individuals at either end of the curve
Disruptive Selection
 When individuals at the _______________________________________ of
the curve have higher fitness than individuals near the center
Genetic Drift
 Random change in allele frequency in _______________________________
Small population may not fit the predicted genetic probabilities

In small populations, individuals that carry a particular allele may leave more
descendants than other individuals, just by ____________________. Over
time, a series of chance occurrences of this type can cause an allele to become
___________________ in a population
Founder Effect
 A situation in which allele frequencies change as a result of the ___________
__________________________________________________ of a population
Hardy Weinberg Principle
 States that allele frequencies in a population will remain constant unless one
or more factors cause those frequencies to change
When genetic frequencies remain constant, it is called _________________
Five Conditions of Genetic Equilibrium
 The five conditions required to maintain genetic equilibrium from generation
to generation are:
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–
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