Transcript Chapter 22

Chapter 22
Descent with
Modification: A
Darwinian View of Life
evolution** – processes that have transformed life
on Earth from its earliest beginnings to its
current diversity
**greatest underlying principle in biology
1859 Darwin published On the Origin of Species
by Means of Natural Selection
arguing that species evolved from ancestral
forms by natural selection
-revolutionized scientific thought, but contrasted
sharply with views of the time
Figure 22.18 Charles Darwin in 1859, the year The Origin of Species was published
Figure 22.0 Title page from The Origin of Species
Figure 22.10 Camouflage as an example of evolutionary adaptation
Linnaeus – (early 1800’s)
“father of taxonomy” – branch of biology
concerned with naming and classifying
diverse forms of life
-developed binomial nomenclature – 2 part
naming system
Cuvier – a paleontologist; proponent of
catastrophism – Earth’s changes are due to
catastrophic events; used fossils to back up his
claim
Hutton & Lyell – geologists; supported idea of
catastrophic events, but changing of Earth
gradually
Lamarck – believed acquired characteristics
could be passed onto organisms (ex: giraffe
neck length)
Darwin’s voyage – 1831 (HMS Beagle)
-took him to Galapagos Islands where he
developed the idea of adaptation to
environment
Wallace – 1858 – developed idea of natural
selection independently from Darwin &
published manuscript (before Darwin, but his
was not as thorough)
Figure 22.5 The Voyage of HMS Beagle
Darwin’s ideas
– descent with modification
- unknown ancestral prototype (no idea of
genetics)
- variation of individuals made differential
reproductive success
- those best adapted (most fit) leave the most
offspring (passing on their characteristics)
Figure 22.9 A few of the color variations in a population of Asian lady beetles
Malthus – many organisms reproduce, few
offspring survive
1930’s – Population genetics – emphasizes
extensive genetic variations within populations
& recognizes importance of quantitative
inheritance
(reconciliation of Mendelism & Darwinism)
1940’s – neoDarwinism – (modern synthesis) –
importance of populations, gradualism, &
modern genetics
Natural selection
-the idea that organisms with favorable traits
are more likely to survive and reproduce
Evidence for evolution:
1) Biogeography – geographical distribution of a
species
ex: endemic island species
(Australia, Galapagos, Madagascar)
2) Fossil record – supports common descent
ex: Archeopteryx links birds, reptiles
3) Taxonomy – reflected branching genealogy
Figure 22.4 Strata of sedimentary rock at the Grand Canyon
4) Comparative anatomy – anatomical similarities
ex: homologous structures, vestigial organs
5) Comparative embryology – helps identify
anatomical homology less apparent in adults;
reflects genetic similarity
ex: comparing embryos of different vertebrates
6) Molecular biology – similarities in DNA
sequences & protein sequences; supports
common descent
Figure 22.14 Homologous structures: anatomical signs of descent with modification
Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates
Chapter 23
The Evolution of
Populations
Population
-a localized group of individuals belonging to
the same species
Species
-a group of populations whose individuals
have the potential to interbreed and produce
fertile offspring in nature
Gene pool
– the total aggregate of genes in a
population at any one time
Hardy-Weinberg theorem
- frequencies of alleles and genotypes in a
population remain constant over time
Hardy-Weinberg theorem
• For a population to be in Hardy-Weinberg
equilibrium, these 5 conditions must be met:
1)
2)
3)
4)
5)
large population size
no migration or emigration
no net mutations
random mating
no natural selection
Hardy-Weinberg equation
p2 + 2pq +q2 = 1
Example
• 500 plants
• 480 red (320 RR, 160 Rr)
• 20 white (rr)
diploid = 1000 alleles
R = 800 (320 x 2 = 640 RR, 160 x 1 = 160
Rr) = 800/1000 = .8 = 80%
r = .2 = 20%
R = p, r = q
(.8)2 + 2(.8)(.2) + (.2)2 = 1
.64 + .32 + .04 = 1
Figure 23.4 Genetic drift
Figure 23.3b The Hardy-Weinberg theorem
Figure 23.3a The Hardy-Weinberg theorem
Microevolution
-relative frequencies of alleles in a
population change over a succession of
generations within a gene pool
Causes of Microevolution
1) Genetic drift – changes due to chance usu. in small
populations
-conditions which may reduce population size:
a) bottleneck effect – population drastically
reduced by disaster, killing unselectively
ex: cheetah population – reduced in the
ice age, then trophy hunted to near
extinction
b) founder effect – genetic drift in a new
colony for that species ex: colonizing isolated
island, lake, etc.
Figure 23.5 The bottleneck effect: an analogy
Figure 23.5x Cheetahs, the bottleneck effect
2) Gene flow – migration of fertile individuals
between populations
3) Mutation – changes in DNA
4) Nonrandom mating - may include:
selective breeding – choosing mates that are
close by (may lead to inbreeding; extreme is
self-fertilization) or assortative mating –
individuals select partners like themselves in
phenotype
Figure 23.16x1 Sexual selection and the evolution of male appearance
5) Natural selection – (variation is at the core)
polymorphism – when 2 or more distinct forms
are present in a population ex: M & F lions
(sexual dimorphism); may be balanced
(remains set in population)
Figure 23.16x2 Male peacock
Figure 23x2 Polymorphism
geographical variation – genetic differences
in population of a species varies regionally
ex: cline – graded change along
geographic
axis
• recombination & mutation add variety
Figure 23.8 Clinal variation in a plant
Variation may be preserved through:
• diploidy – hides recessive alleles
• balanced polymorphism – heterozygote
advantage ex: sickle cell anemia
Aa – resistant to malaria
AA – susceptible to malaria
aa – sickle cell anemia
Figure 23.14 Diversifying selection in a finch population
Figure 23.12x Normal and sickled cells
Figure 23.10 Mapping malaria and the sickle-cell allele
Fitness – relative contribution an individual
makes to the gene pool of the next
generation
Relative fitness – contribution of a genotype to
the next generation compared to the
contributions of alternative genotypes
for the same locus
Modes of Natural Selection
1) Stabilizing selection – favors the mean
2) Directional selection – favors one extreme
phenotype over another
3) Diversifying selection – favors both ends of
the spectrum, & not the mean
**natural selection acts on individuals, but
populations evolve
Figure 23.12 Modes of selection