SAT Subject Test Biology Review Evolution R. Guido, Instructor May-June 2013 Evolution

Change in genes of a population over time

Microevolution - change in 1 population over generations

Macroevolution - speciation or changes that produce an entirely new species

Population - all members of a single species living in a speciﬁc area Evidence of Evolution

1. Fossil record

2. Comparative anatomy

3. Comparative biochemistry

4.Comparative embryology

5. Molecular biology

6. Biogeography Fossil Record

99% all organisms that ever lived have become extinct

Prokaryotic cells are the oldest fossils

Earth is approx. 4.6 billion years old, based on radioactive dating & half-life

Transitional fossils

Link older extinct fossils to modern species

E.g. Archaeopteryx - fossil that is both reptile & bird Comparative Anatomy

Organisms having similar anatomical features are related to each other & share a common ancestor:

1. Homologous structures

Same structure but different function

E.g. Wing of a bat, ﬁn a whale, arm of a human

2. Analogous structures

Different structure but same function

Reﬂects an adaptation of different species to the same environment

However, NOT evident of a common ancestry

E.g. Wing of a bat, wing of a ﬂy

3. Vestigial structures

Evidence that animals have evolved

E.g. Human appendix was once useful based on the diet of prehistoric humans Comparative Biochemistry

The more closely organisms are related, the more similar their biochemistry

E.g. Insulin of pig & human

Comparative Embryology

Closely related organisms go through similar stages of embryonic development

Stages appear so similar that it is difﬁcult to determine which organism is developing Molecular Biology

Aerobic organisms contain a polypeptide called cytochrome c, needed to carry out cell respiration

The amino acid sequence of this molecule is similar among closely related organisms

Biogeography

Theory of Continental Drift

Continents were locked together approx 250 million years ago

"Supercontinent" called Pangaea

Slowly separated over the course of 150 million years

Fossil evidence conﬁrms marsupials (e.g. Kangaroos) migrated from land of South America to Antarctica before settling in Australia Lamarck

Theory of Inheritance of Acquired Characteristics

Stated that individual organisms changed in response to their environment

E.g. Giraffe developed a long neck due to stretching for leaves high on the Acacia tree

The stretching was an acquired trait that was passed on to offspring

Theory of Use & Disuse

The more an organ or structure is used, the more developed it will become in future offspring Darwin Theory of Natural Selection

1.Overpopulation - Populations tend to grow exponentially & exceed their resources

2.Struggle for existence - organisms compete for limited resources

3.Variation - unequal ability of certain organisms to survive long enough to reproduce

4.Survival if the Fittest - only those individuals best adapted tot he environment will survive, reproduce, & pass on those traits to their offspring

5.Speciation - Evolution occurs as an accumulation of advantageous traits in a given population

Note: Source of Variation was not well understood until Mendel proposed his theories of Genetics in the late 1800's & DeVries described mutations in the early 1900's Process alters the frequencyNatural of inherited traitsSelection in a population by the following mechanisms:

1.Stabilizing Selection

Eliminates extreme traits & favors the "middle ground" or more common forms

Mutants are weeded out

E.g.: human birth weight is favored to be in the middle at 7.5lbs or between 6 & 9 lbs 2. Disruptive (Diversifying) Selection

Favors extreme types in a population at the expense of the middle ground

May result in the formation of a new species

E.g: 2 colors of shells in snails 3. Directional Selection

Change in environment induces 1 phenotype to replace another

E.g: Industrial Melanism - the Peppered Moth Sources of Darwin's Variations 1. Mutation

Changes in genetic material

Agent of Evolution

2. Genetic Drift

Change in the gene pool due to chance

Types

A.Bottleneck Effect

Natural disasters result in loss of genetic variation due to decrease in population size

Result is a smaller population with certain alleles either under-represented or over-represented compared with the original population

B Founder Effect

When a small population breaks away from a larger one to a new area

Again, certain alleles may be under- or over-represented

3. Gene Flow

Movement of alleles into or out of population Hardy-Weinberg Equilibrium

Theory that describes a stable, non-evolving population where allelic frequencies do not change

Criteria for a population to remain in Hardy-Weinberg Equilibrium:

1.Population must be large - any subtle changes in alleles will not impact on overall allelic frequency

2.No migration - population must be isolated from others

3.No mutations - no changes in genes

4.Mating must be random - if mating is selective, then most ﬁt will have a reproductive advantage and initiate evolution of population

5.No natural selection - no changes in allelic frequencies of gene pool Hardy-Weinberg Equation Used to calculate frequencies of alleles in population

p2 + 2pq + q2 -Or- p + q = 1 where, p = dominant allele q = recessive allele p2 = homozygous dominant individuals 2pq = heterozygous dominant individuals q2 = homozygous recessive individuals Isolation & Speciation

Isolated populations:

Subject to different selective pressures in their environments

As a result, they may accumulate enough changes to become a new species Forms of Isolation

1. Geographic isolation - occurs when species become separated

2. Polyploidy - type of mutation that results in extra sets of chromosomes

3. Habitat isolation - when 2 organisms live in the same area but rarely encounter each other, e.g. 2 species of snake, 1 lives in water, the other on land

4.Behavioral isolation - when 2 animals become isolated because 1 undergoes a change in behavior

5. Temporal isolation - different plants of 1 species living in same area may separate into 2 populations due to blooming at different time periods

6. Reproductive isolation - closely related species cannot mate due to anatomical differences, e.g. Large & small dog breeds Patterns of Evolution

How species evolve is categorized into 5 patterns:

1. Divergent evolution - when population becomes isolated from rest of species & begins to evolve into its own species due to selective pressures from environment, i.e. species A & species B evolving from a single common ancestor 2. Convergent evolution - when unrelated species occupy same environment, exhibit similar adaptations, e.g. Whales & Sharks

3. Parallel evolution - 2 related species making similar adaptations in different regions e.g. North American wolf & Tasmanian wolf 4. Coevolution - set of adaptations between 2 interacting species, e.g. Pollinators & plants, predator & prey

5. Adaptive radiation - evolution of many species from a single common ancestor, e.g. Darwin's ﬁnches - 14 different species occupying a different ecological niche Theories about Evolution

1. Gradualism

Organisms descend from a common ancestor slowly over time

Accumulation of small changes into a new species

Scientists generally don't accept theory due to lack of evidence in fossil record

2. Punctuated Equilibrium

New species appear suddenly after long periods of no change

Generally accepted by scientists who believe that ancestral species become extinct and are replaced by new species Heterotroph Hypothesis Earth's age is approx. 4.6 billion years old

Ancient atmosphere made of:

Methane

Ammonia

Water vapor

Free nitrogen

No free oxygen

Heat, lightening, UV. Radiation provided energy for chemical reactions to give rise to the ﬁrst cell

Hypothesis states that 1st cells were anaerobic heterotrophic prokaryotes that evolved approx. 3.5 billion years ago

Absorbed organic molecules from environment Heterotroph Hypothesis

Eukaryotic cells evolved from prokaryotes about 1.5 billion years ago - possessed nucleus, membrane-bound organelles

Endosymbiotic theory - describes how small bacteria took up residence inside large prokaryotic cells & performed functions in a symbiotic relationship, leading to formation of organelles Heterotroph Hypothesis 1st multicellular animal appeared approx 565 million years ago

Within 40 million years, the phyla for all animals evolved - Cambrian era explosion

Characteristics enabled animals to move from water to land:

Lungs

Skin

Limbs

Internal fertilization

Hard, external shell

Characteristics enabled plants to move from water to land:

Roots

Supporting cells to capture light

Vascular tissue for transport of water, minerals

Waxy cuticle to protect leaves

Seeds Evolution of Mammals

Mammals appeared approx 210 million yrs ago

Primates - apes appeared about 25 million yrs ago

Humans & apes co-evolved from a common ancestor approx 10 million yrs ago

Human ancestors arose ﬁrst in Africa

Homo sapiens, modern human, arose approx 150,000 yrs ago