GMU BIOL 102 Dr. Gleason Exam II

Week 6

Natural Selection

Charles Darwin

Studies finches in the Galapagos in 1835

Population

A group of individuals that belong to the same species and live in the same area

Evolution

The gradual change in a species over time

Variations

Differences within a population- inherited from parents

DNA mutations are the ultimate source

Unity

Descent from a common ancestor

Diversity

Modifications that evolve as a species diverged from ancestors

Individual Evolution

Not possible-- species evolve as one trait becomes favorable over another in terms of survival

Fitness

The ability of an animal to survive and reproduce

Genotype

The genetic code expressed by phenotypes

Speciation

If a species changes enough via natural selection it may become a new species

New species are descended from a common ancestor and share many characteristics

Methicillin-resistant Staphylococcus aureus (MRSA)

a strain of the bacterium Staphylococcus aureus that has become resistant to the antibacterial action of the antibiotic methicillin, a form of penicillin

Staphylococcus aureus (Staph)

Bacteria that is mostly harmless to people that carry them, but can cause infections that damage skin.

Approx. 30% of the population carries it

Approx. 2% carries MRSA strains

Most individuals who carry the bacteria are disease free

MRSA

Transfers from person to person through direct contact

Athletes are at higher risk due to increased contact

Developed resistance to most antibiotics

Adverse effects on people with weakened immune systems

Antibiotics

Interfere with the function of essential bacterial cell structures

Beta-lactams

Most commonly prescribed class of antibiotics

Work by interfering with a bacterium's ability to synthesize cell walls

Binary Fission

A form of asexual reproduction in single-celled organisms by which one cell divides into two cells of the same size

Random Mutations

Can create new alleles that cause some bacteria to be resistant to antibiotics

Gene transfer

Can spread alleles for antibiotics resistance to other bacteria

adaptive radiation

Where organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available

Causes for adaptive radiation

New opportunities

Lack of competitors

Varying habitats and food sources

Evolution of new structures

When a few organisms colonize

Mass extinction

event in which many types of living things become extinct at the same time

Gene pool

All the genes, including all the different alleles for each gene, that are present in a population at any one time

Microevolution

Change in allele frequencies in a population over generations.

Survival of the Fittest (Natural Selection)

individuals that are better suited to their environment survive and reproduce most successfully

Can only act on existing variation

Hardy-Weinberg Equilibrium

allele and genotype frequencies in a population will remain constant from generation to generation unless an outside force acts to change those frequencies

Hardy-Weinberg Conditions

1. No mutations

2. Random mating

3. No natural selection

4. Extremely large population size

5. No gene flow

Main causes of evolutionary change

genetic drift, gene flow, natural selection

Alterations to Variation

Stabilizing selection, Directional Selection, Disruptive selection

stabilizing natural selection

average individuals in a population have an advantage

Directional Selection

occurs when natural selection favors one of the extreme variations of a trait

disruptive selection

form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

Natural Selection in Bacteria

Antibiotics change the environment in which bacteria live

When antibiotics are present, the bacteria that is resistant will have the greatest fitness

Directional selection for antibiotic resistance

Week 7

Evolution of Populations

Species

a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding.

Result from speciation

The Biological Species Concept

Species is a group of populations whose members have the potential to produce fertile offspring.

reproductive isolation

Separation of species or populations so that they cannot interbreed and produce fertile offspring.

Essential factor in evolution

The Morphological Species Concept

based on observable physical traits and can be applied to asexual organisms and fossils

The Ecological Species Concept

A definition of species in terms of ecological niche, the sum of how members of the species interact with the nonliving and living parts of their environment.

The Phylogenetic Species Concept

A definition of species as the smallest group of individuals that share a common ancestor, forming one branch on the tree of life.

Reproductive Barriers

anything that prevents individuals of closely related species from interbreeding

Prezygotic Barriers

A reproductive barrier that impedes mating between species or hinders fertilization if interspecific mating is attempted

Examples of Prezygotic Barriers

habitat isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation

Postzygotic Barriers

Barriers that prevent the hybrid zygote from becoming a fertile adult.

Examples of Postzygotic Barriers

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

Examples of Reproductive Isolation

Geographical isolation, temporal isolation, behavioral isolation, mechanical isolation, gametic isolation, hybrid inviability, hybrid infertility

Genetic Drift

A change in the allele frequency of a population as a result of chance events rather than natural selection.

The smaller the population, the greater effect of the genetic drift

gene flow

Movement of alleles into or out of a population due to the migration of individuals to or from the population

Founder Effect

Genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of that of the original population.

Bottleneck Effect

A change in allele frequency following a dramatic reduction in the size of a population

Nonadaptive Evolution

Any change in allele frequency that does not by itself lead a population to become more adapted to its environment; the causes of nonadaptive evolution are mutation, genetic drift, and gene flow.

Inbreeding

mating between closely related individuals

Does not change allele frequency within a population

Increases the proportion of homozygous individuals to heterozygous

Inbreeding Depression

when individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce

Hardy-Weinberg equation

p^2 + 2pq + q^2 = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. It predicts the frequency of homozygous dominants, homozygous recessives, and heterozygotes.

Week 8

Human Evolution

Characteristics of Primates

Limber Joints

Grasping hands and feet with flexible digits

Short snout

Forward pointing eyes that enhance depth perception

Primates are divided into three groups

1. Lemurs, lorises, bush babies

2. tarsiers

3. arthropods (including monkeys and apes)

Hominins

Humans and their immediate ancestors

Paleoanthropology

the study of the history of human evolution through the fossil record

Timeline of Human Evolution

Non-linear, many species lived during the same time periods

Hominidae

Of current species, chimpanzees are most closely related to humans

Ardipithecus ramidus

Species 4.4 mya characterized by small brain, ability to both walk upright and on all fours in trees

Australopithecus

Species 2.6 mya characterized by ability to walk upright, live on the ground, and use tools

Homo erectus

"Upright man" these hominids 800,000 years ago became skillful hunters and invented more sophisticated tools for digging, scraping and cutting. They also became the first hominids to migrate from Africa. Also were the first to use fire.

Homo sapiens

A species of the creatures Hominid who have larger brains and to which humans belong, dependent of language and usage of tools.

Difference between present-day humans and chimpanzees

Humans walk bipedal

Humans have much larger brains

Homo neanderthalensis

Had a brain even larger than ours

Hunted big game with tools made from stone and wood

Humans evolved in Africa

Humans originated in Africa

A group migrated to other continents

Fossil records show earliest modern humans lived in Africa

Mitochondrial DNA (mtDNA)

genetic material in the mitochondria of the cytoplasm of a cell; only inherited from the mother

mutates at a regular rate

A mother with a mutation in her mtDNA will pass it on to her children

We can track human ancestry and build an evolutionary tree

Human Skin Tone

Determine by levels of melanin

Correlates with geography

Based on relative position to earths poles

Melanin

A pigment that gives the skin its color

More melanin=darker skin

Levels are genetically determined

Absorbs UV light

Melanin levels in skin can affect nutrient levels in body

Low UV light

People with low melanin levels can form more vitamin D than those with more melanin

Vitamin D

A fat-soluble vitamin used to maintain a healthy immune system and build healthy bones and teeth

Produced when skin is exposed to UV light

High UV light

People with high melanin levels can prevent folate degradation better than those with low levels

Folate (folic acid)

Helps prevent birth defects, Key element for new cell creation

(Cereals, asparagus, orange juice)

Allele Selection

Can be positive, negative, or neutral

Positive Selection

natural selection that increases the frequency of a favorable allele

Negative Selection

natural selection that decreases the frequency of a harmful allele

neutral selection

differences in DNA sequence that do not confer a selective advantage or disadvantage

Week 9

Population Ecology

Ecology

The study of how living things interact with each other and their environment

Community

Interacting populations of different species in a defined habitat

Ecosystem

Living organisms in an area and the nonliving parts of the environment with which they interact

Counting Wildlife Populations

Researchers count the individuals within designated areas and then estimate the total

Random Distribution

Individuals are equally likely to be anywhere within the area

Clumped Distribution

High density clumps are separated by areas of low abundance

Uniform Distribution

Individuals maximize space between them by being uniformly spaced

population growth rate

the difference between the birth rate and the death rate

influenced by movement of individuals into a population and movement out of a population

Exponential Population Growth

Growth of a population in an ideal, unlimited environment, represented by a J-shaped curve when population size is plotted over time.

Logistic Population Growth

population growth that levels off as population size approaches carrying capacity

Population Carrying Capacity

number of organisms that can be supported by a given environment

Boom and Bust Cycle

a pattern of population growth in which exponential growth leads to a period when the population exceeds its carrying capacity, causing the population to decrease rapidly or crash

density dependent factors

A factor that influences population size and growth depending on the number and crowding of individuals in the population

ex: predation

density independent factors

A factor that influences population size and growth regardless of the number and crowding within a population

ex: weather

Abiotic Factors

Nonliving components of environment.

Biotic Factors

Living components of an environment