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Chapter 23
The Evolution of
Populations
I. Mutation and Sexual reproduction
produce variation.
• A._________n shows a
pattern of change in the
allele frequency of a gene in
a population.
– _______ (in sex cells) are the
source of new genes and new
alleles.
– Point mutations change little,
chromosomal mutations
cause greater changes.
– Sexual _________ (crossing
over, IA, and random
fertilization) account for most
variation.
II. Population Genetics
• A. _________genetics
is the study of the
genetic variation within
a population and how it
changes over time.
– 1.A _________ is a
localized group of
individuals that belong
to the same species.
– 2A ______ is a group of
populations which can
interbreed and produce
fertile offspring.
• B.The _________ consists of all the alleles present
within a population.
– If all members of the populations are __________ for
the same copy of an allele, the allele is referred to as
“fixed”.
• C.The ________________ theory states
that the frequency of an allele remains
constant in a population unless acted on by
something other than Mendelian genetics
and recombination.
– Results in Hardy-Weinberg __________, a
stable, unchanging population.
– The Hardy-Weinberg ________ allows us to
predict the allelic frequencies in a population.
p2+2pq+q2 =1,
where p+q=1…so, p=1-q and q=1-p
D. In order for a population to be in
Hardy-Weinberg equilibrium, it must:
• 1. Be a ______ population.
• 2. Have no _______ (gene flow).
• 3. Have no net _________.
• 4. Have _________ mating.
• 5. Not be subject to _______ ________.
Populations that meet the Hardy-Weinberg
equilibrium are ______________.
III. Causes of Microevolution
• A. Mutations alter
_______
frequencies, but
they are rare.
• B. The 3 main
sources of change
in _______
frequency are:
• 1. __________ is a change in the gene pool
of a small population.
– a. The ______ _____ occurs when the numbers
in the population are reduced to such low levels
that the gene pool is diminished. Some alleles
may be underrepresented or overrepresentated.
• b. The _____________ occurs when a few
members of a population colonize an
isolated location.
– Polydactyly in the Amish.
• 2. ________ refers to genetic exchange due to the
migration of individuals or gametes between
populations.(emigration or immigration).
• 3.Natural selection is the __________
reproductive success of organisms.
IV. Genetic Variation
• A. ______________ refers to the
differences in quantitative characters such
as height, hair color, eye color.
__________ occurs when 2+ forms of a trait are
present in a population.
•
_________variation occurs when differences occur
between populations because of environmental differences
in where they live.
Clinal variation in plants-height decreases with increasing
Elevation.
• 1.Having a diploid # of chromosomes
(__________) allows organisms to hide
genetic _________ (recessive alleles).
2.______________
advantage is a
benefit that
comes from the
heterozygous
condition.
Sickle cell anemia
and malaria>>>
V. Modes of Selection
• A.__________ selection acts ________ the
_________ and favors the middle.
• B. ___________ selection favors one of the
extremes.
• C. ________ selection favors both
extremes.
Sexual Selection
Sexual __________ occurs when the male
and female of a species look different.