Transcript Evolution-Hardy Weinberg Criteria PPT Lecture

CHAPTER 23
(PART 2) HARDY
WEINBERG
CRITERIA &
POPULATION
EVOLUTION
(PART 3)
Ms.Gaynor
AP Biology
Causes of Microevolution
A change in the gene pool of a population
over a succession of generations
• We use 5 criteria for nonevolution to determine causes of
microevolution
• The Hardy Weinberg equations
are used to determine the degree
of microevolution that is
occurring for a given allele
Cause #1: Small Populations
How can this happen? Genetic Drift
• Genetic drift:
changes in the
gene pool of a
SMALL
population due to
chance
(usually reduces
genetic
variability)
•
•
http://highered.mcgrawhill.com/sites/0072835125/student_vie
w0/animations.html#
2nd to last video
Genetic Drift Example #1
The Bottleneck
Effect
• Results from a
reduction in
population
(natural
disaster) such
that the surviving
population is no
longer genetically
representative of
the original
population
Ex: NORTHERN ELEPHANT SEAL
Genetic Drift Example #2
Founder Effect:
a cause of
genetic drift
due to the
colonization
by a limited
number of
individuals from
a parent
population
http://bcs.whfreeman.com/thelifewire/conten
t/chp24/2402002.html
Founder Effect in Amish
Causes dwarfism and polydactyly
http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m2/s4/evm2s4_7.ht
m
Cause #2: Migration of Alleles
Gene Flow:
genetic exchange
due to the
migration of
fertile individuals or
gametes between
populations
(reduces
differences
between
populations)
Cause #3: Mutations
Mutations:
• a change in an organism’s DNA
• original source of genetic
variation (raw material for natural
selection)
• Mutations can immediately alter p and q in
a population
• Individual mutations are rare in a
population, but there may be cumulative
mutations that have an effect  cause
evolution
Cause #4: “Picky” Mating
Nonrandom
mating
• “picky” mating
• Unequal
chances of each
egg getting
fertilized
• Assortative
mating choosing
individuals
more like self
Sexual Selection
• Sexual selection is natural selection for
mating success
• It can result in sexual dimorphism,
marked differences between the sexes in
secondary sexual characteristics
• Intrasexual selection
– competition among individuals of one
sex for mates of opposite sex
• Ex: Males competing for female attention
• Intersexual selection
– when individuals of one sex (usually
females) are choosy in selecting their
mates of the other sex
– Selection may depend on the
showiness of the male’s appearance
Sexual Dimorphism
• Males are usually
more colorful and
larger
• Does NOT help cope
with environment
• DOES lead to
reproductive success
• Can be termed
“Female Selection”
Cause #5: Natural Selection
Natural Selection
• differential reproductive
success in reproduction due to
variation
• only form of microevolution that
adapts a population to its environment
– Phenotypes are selected FOR or
AGAINST (not genotypes)
• In a population at equilibrium, no
phenotypes (therefore, alleles) are
selected over other alleles
•
http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m2/s1/evm2s1_6.htm
Animations to Review Hardy
Weinberg and its Criteria
• http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Fl
ash/life4e_15-6-OSU.swf
• http://www.hippocampus.org/Biology;jsessionid=76E1
5D24965DEE7E98227392E980A13C
• See video called “Population Genetics” through
“Mechanisms of Evolution”
3 Modes of Natural selection
• Directional selection favors individuals
at one end of the phenotypic range
• Disruptive selection favors individuals at
both extremes of the phenotypic range
• Stabilizing selection favors intermediate
variants and acts against extreme phenotypes
•
http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/17_A02.swf
DARK ROCK HABITAT
LIGHT/DARK ROCK
HABITAT
MEDIUM COLOR ROCK
HABITAT
Sources of Variations
1. Mutations
–At first the mutation may not be
beneficial to the organism
(resistance to antibiotics)
–Once antibiotics are introduced
the mutation is beneficial
2. Sexual recombination
increases variation
Population variation
Polymorphism
coexistence of 2 or
more distinct forms of
individuals (morphs)
within the same
population
Geographical
variation
differences in genetic
structure between
populations (cline)
SPRING
SUMMER
Evolutionary Fitness
• The phrases “struggle for existence”/“survival
of the fittest” are commonly used to describe
natural selection but can be misleading
• Reproductive success is more subtle and
depends on many factors
» Fitness is determined by
REPRODUCTIVE AND SURVIVAL
success of individual
• Variations & natural selection affect fitness
• Sterile individuals even with a relatively fit allele
will not be considered fit overall (=0)
• Fitness is not determined by one trait but by the
totality of traits in the organism
A 4th Type of Natural
Selection: Neutral Variation
• Neutral variation is
genetic variation that appears to
favor NO selective advantage
• Frequencies can change but no
advantage/ disadvantage for
population
Asexual vs. Sexual
Reproduction
• Sexual reproduction produces
FEWER reproductive offspring
than asexual reproduction
– a so-called “reproductive
handicap”
• Sexual reproduction produces
genetic variation
LE 23-16
Asexual reproduction
Female
Sexual reproduction
Generation 1
Female
Generation 2
Male
Generation 3
Generation 4