Download Evolution Chapters 22-24

Evolution Chapters 22-24
Chapter 22
1. Evolution means, Species change over time. Ancestral Species of past gave rise to new species of
today.
2. Events and persons influencing Darwin’s thinking:
a. 1735-1788: Carolus Linnaeus published classification of organisms and developed binomial
nomenclature.
b. 1790: Hutton proposes that rocks have changed very slowly over time and continue to do
so.
c. 1798: Malthus publishes ‘Essay on principle of population’.
d. 1809: Lamarck proposes his theory of evolution and Darwin is born.
e. 1812: Cuvier establishes Paleontology, the study of fossils by extensive study of vertebrate
fossils strata in sedimentary rocks. He explained the gaps between fossils due to
Catastrophism.
f. 1831-36: Darwin traveled on HMS Beagle around the world and collected specimens
especially from South America.
g. 1859: Darwin published ‘On the Origin of Species’.
3. Lamarck proposed the 1st important theory of evolution in 1809.
a. Use and Disuse: Use of organs, develop them and disuse reduces them.
b. Inheritance of Acquired Characters: Acquired characters over life time pass to next
generation. This is not true. Bonsai trees produce seeds developing into normal trees.
4. Darwin explained evolution by natural selection by ‘Descent with Modification’ in 1859
5. Descent with modification means species living today are descendants of species living in past. It
explains unity in diversity.
6. Natural selection brings match between the organisms and environment. It leads to adaptation of
species to its environment.
7. Variations: The members of a population have small differences from one another, heritable
variations.
8. All species reproduce higher than resources can support. It leads to competition for resources.
9. Individuals with heritable traits favoring survival reproduce more. Individuals without favorable
variation survive less and reproduce less. It results in adaptation and can lead to speciation. For
example, Galapagos finches. Camouflaging matches organisms to environment. Environmental
factors vary from place to place. Therefore, adaptations in one place may be useless or detrimental
in other places.
10. Artificial selection by humans in pigeons and varieties of vegetables (kale, cabbage, broccoli,
kohlrabi) from wild mustard supports natural selection.
11. Natural selection operates on individuals but unit of evolution is population and not individuals in it.
Individuals do not evolve over time but populations do.
12. Microevolution is a change in allele frequencies of a population and may help it to survive and
reproduce better in its ecosystem. It leads to a biological adaptation.
13. Macroevolution is origin of a new species from ancestral species leading to higher groups.
14. Fossils are remains or imprints of organisms living in remote past. Organisms buried in sedimentary
rocks undergo mineralization. It preserves the detailed structures of fossils for millions of years.
15. Fossils provide best evidence for evolution.
16. Other evidences come from anatomy (vestigial organs), embryology (all vertebrate embryos have
similar early development) and molecules (hemoglobin in closely related species has few amino
acids different).
17. Resistance to drugs of HIV or other pathogens, and resistance to pesticides are recent evidences of
evolutionary adaptations.
Homologous Structures
1. Share Common ancestry and basic plan
2. Same structures used for different functions
3. Leads to divergent evolution
4. For example bones of forelimb, hindlimb or skull
5. Used as a basis for classification
Analogous Structures
1. Different ancestry and basic plan
2. Different structures used to do similar
function
3. Leads to convergent evolution
4. For example wings of insects and birds
5. Leads to artificial groups if used in
classification
Evolution at molecular level
18. Molecules like DNA, RNA and proteins have records of evolutionary history = phylogeny
19. Closely related organisms like chimps and humans separated in near past and have lesser
differences in arrangement of amino acids in proteins or nucleotides in nucleic acids
20. Number of differences increase steadily as we move from closer to distant related species.
Chapter 23
Five Agents of Evolution
1. Mutation
a. Mutation is the change in nucleotide sequence of a gene or chromosome.
b. Mutation rate is very low
c. Most mutations are harmful
d. Mutation is the ultimate source of variations
e. For example, sickle-cell-anemia is a single nucleotide mutation in hemoglobin gene
2. Migration or Gene Flow
a. Occurs due to movement of individuals from one population to another
b. Depends on # of individuals and what kind of genes they carry
3. Genetic Drift
a. Explains role of chance in evolution
b. Operates best in small and endemic populations
c. Brings different results from natural selection
d. Founder Effect is when some individuals colonize a new area.
e. Bottleneck effect is population size gets very small and regains its size.
4. Non-random mating
a. Selection in mating results in changes in gene frequencies
b. Mostly females chose their partners favoring different traits in different species
c. Horns in deer and colored feathers in birds reflect a healthy genotype
5. Selection
a. Natural Selection operates by Favorable allele  more survival  more
reproduction  more % in next generation
b. For example, Resistance allele against DDT or antibiotic
c. Artificial Selection by humans has lead to formation of different breeds in dogs and
varieties in plants – cabbage and cauliflower
3 kinds of Natural Selection
a. Stabilizing NS operates when environment is stable and population is already adapted.
Changes are not welcome; middle favored.
b. Disruptive NS operates when large changes occur in environment. Middle eliminated and
ends favored; lead to formation of new species.
c. Directional NS operates when environment changes gradually in 1 direction. One end
eliminated other favored. DDT resistance.
21. Sickle-Cell Anemia is an example of point mutation, a change of single base of DNA
a. Glutamic acid is replaced by Valine in position 6 out of 146 amino acids in β chain of
hemoglobin
b. Reduces life span of RBC’s
c. Change shape only under stress
d. Present in certain African and Asian populations where malaria is common. If both genes are
normal malaria kills you and if both genes are defective sickle cell anemia does. Therefore,
many adaptations are a compromise between 2 or more situations.
22. Some Genetic Terms:
a. Characters/traits are controlled by discrete units called genes. For example, Height of Pea
plant is a trait and so is the color of flower, seed or pod.
b. A gene has 2 alternate versions called Alleles. Yellow or green seeds in pea are controlled by
2 alleles of same gene.
c. Parents carry 2 alleles for each character but the gametes carry only 1 allele. In body cells
with 2 alleles when both are similar = homozygous (YY or yy) and when different =
heterozygous (Yy).
d. When 2 different alleles come together only one determines the appearance of body
(dominant) and the other remains hidden (recessive). For example Yellow seed color
dominates green seed color. Though recessive allele does not express but maintains its
identity.
e. Phenotype = physical appearance, yellow and green seeds in pea Genotype = genetic
make-up, Yy
f. Gene Pool is aggregate of all alleles in a population. Each population has a unique gene
pool.
23. Hardy-Weinberg Principle: it states that allele and genotype frequencies in a population remain
constant from generation to generation if population is large, there is negligible mutation, mating is
random, there is no gene flow and no natural selection.
24. Frequency of 2 alleles of a gene is p + q = 1
25. Frequency of first allele is p = 0.6 therefore frequency of other allele is q = 0.4 (1.0-0.6)
26. Expected allele frequency in next generation is p2 + q2 = 2pq = 1. Calculate it by using above values
of p and q.
Chapter 24
27. Speciation: origin of a new species;
a. Raw Material: Genetic variations: provided by mutation, independent assortment and
recombination (crossing-over).
b. Driving Forces are primary Natural selection and secondary genetic drift.
c. End product: Reproductive Isolation leads to Speciation. Pre-zygotic and Post-zygotic
barriers
d. Reproductive Isolation:
e. Allopatric speciation – populations live in different geographical area
f. Sympatric speciation – same geographical area; populations are isolated due to use of
different parts of habitat or have different breeding seasons (ecological isolation)
28. Polyploidy (3n or more)
a. Plants can tolerate extra genomes of chromosomes
b. Increase in # of genomes usually produces bigger plants or parts like flowers or fruits
c. Polyploidy is a type of instant speciation
d. Bread Wheat has 6n chromosomes in it.
29. Macroevolution: Speciation leads to emergence of higher taxons like insects, mammals and
flowering plants. Extinction of some taxons and emergence of new taxons, getting bigger or
shrinking in size, brings major changes in related taxons over long time.
30. Rate of evolution: can be slow or fast
a. Gradualism means very slow but steady rate of evolution over millions of years.
b. Punctuated Evolution means long spells of little or no change intervened by short spans of
fast change.