Bio 1B First Midterm

Evolution unit

Origin of the universe theory

formed from a singularity approximately 13.8 billion years ago, leading to the expansion known as the Big Bang.

What is a singularity?

an extremely large mass occupies a very small space, led to the big bang

Origin of the universe

~13.8 billion years ago

Origin of earth

~4.5 BYA

Origin of life

~3.8 BYA; stromalites in Australia

Origin of anatomically modern humans

~200,000 years ago

evidence that all life derives from a common ancestor

shared molecules (amino acids and nucleotides), shared macromolecules (DNA, RNA, etc.), shared mechanisms of DNA replication, common genetic code, similarity of form, and similarity of DNA sequences

the three domains of life

bacteria, archaea, and eukarya

archaea

single celled microbes identified from rRna genes; can use a variety of energy sources and live in extreme environments

bacteria

single celled organisms that live in most environments; can be beneficial or pathogenic; distinict from archaea

eukaryotes

protists (single celled organisms) , plants, animals, and fungi

prokaryotes are….

archaea and bacteria

key differences between prokaryotes and eukaryotes

eukaryotic cells contain membrane bound organelles (mitochondria or chloroplasts), chromosomes are contained in membrane-bound nucelus, whereas prokaryotes keep theirs in non-membranous nucleioid; prokaryotic cells don’t contain organelles or a nucelus, smaller than eukaryotes

Are archaea more closely related to eukarya or bacteria?

eukarya

What unites archaea and eukaryotes?

components of DNA replication, transcription, and translation; more than 30 ribosomal proteins shared between the two; translation factors; similar RNA polymerases

the two parts to evolution

Anagenesis and cladogenesis

Anagenesis

the change in a lineage over time

Cladogenesis

the splitting of one lineage into two (speciation)

example of evolutionary change

antibiotic resistance and penicillin

four criteria for evolution by natural selection

variation, inheritance, exponential growth, and differential success

variation

individuals within a population are variable

inheritance

the variations among individuals are, at least in part, passed from parents to offspring; offspring resemble their parents

exponential growth

all species produce more offspring than their environment can support

differential success

some traits confer an advantage to survival or reproduction, thus leaving more offspring with these traits

Antecedents to Charles Darwin

Carl Linnaeus, Georges-Luis Leclerc/Comte de Buffon, Erasmus Darwin, Jean-Baptise Lamarck, Thomas Robert Malthus, and Charles Lyell

What did Carl Linnaeus contribute to science?

Estab. modern classification system for plants and animals

What did Georges-Louis Leclers contribute to science?

studied biogeography, entertained idea of evolution, thought the earth might be very old

What did Erasmus Darwin contribute to science?

entertained idea that all species originated from a common ancestor

What did Jean-Baptise Lamarck contribute to science?

argued for evolution through inheritance of acquired characteristics

What did Thomas Robert Malthus contribute to science?

population multiplies geometrically and food arithmetically; population will eventually exceed food supply

What did Charles Lyel contribute to science?

developed assumption of uniformitarianism: processes we see today also acted in the past; wrote “Principles of Geology”

Lamarckian evolutionary theory

disproven, first mechanism of evolution; giraffes use their long necks, which makes them longer; giraffes who use their necks a lot will pass this trait down to their offspring

homology

different species with similar structures, even if structures have different purposes (arms and wings); similarities due to shared ancestry

analogy

species or features exist because they evolved separately (no genetic ties) to serve a common purpose; similarities due to convergent evolution (wings of birds v. bats)

biogeography

greater similarity of species within continents than between continents, even in comparison of similar habitats

other biologist who saw evidence for natural selection around the same time as Darwin

Alfred Russel Wallace

adaptation

a trait gained because of natural selection that enhances the ability of an organism to survive or reproduce in a particular environment

alleles

alternative versions of genes that differ in nucleotide sequence; different alleles may produce differences in character expression (ie. phenotypic differences)

deoxyribonucleic acid (DNA)

the molecule of inheritance in most organisms; a double-stranded helical molecule consisting of long sequences of four nucleotides: adenine, thymine, cytosine, and guanine

differential success

the greater survival and reproduction of organisms with some traits compared with organisms that do not have those traits

evolution

change over time in the genetic composition of species; change in allelle frequency as a result of mutation, natural selection, genetic drift, or gene flow

fixation

the change in a gene pool from a situation where there are at least two variants of a particular gene (allele) to a situation where all individuals possess only one of the alleles

gene

a section of a DNA strand (ie. a sequence of nucleotides) that determines the sequence of amino acids in the protein for which it codes

gene flow

the movement of genes among populations due to migration and interbreeding; reduces genetic differences between populations

genetic drift

random changes in allele or genotype frequencies within a population; bottleneck or founder events

heterozygous

having different alleles for a given gene

heterozygosity

in a population, the average proportion of genes for which a randomly chosen individual is heterozygous

homozygous

having two copies of the same allele for a given gene; an individual can be homozygous for some genes and heterozygous for others

mean

arithmetic average between a set of values

macroevolution

evolution across geologic timescales (generally millions of years), involving groups of species

microevolution

evolution within a population, over shorter timescales than those examined in macroevolution

mutation

a change in the nucleotide sequence of a gene in an individual

null hypothesis

an assertion that there is no relationship among observations, that the relationship is due to chance, or than an experimental treatment has no significant effect; usually contrasted with an alternative hypothesis that some mechanism produced the pattern

phenotype

the physical or morphological expression of a genotype in a given environment

population

a group of interbreeding individuals that belong to the same species and occupy a similar geographic area

population genetics

an approach to understanding microevolution that combines mathematical theory and experimental data to understand the effects of mutation, genetic drift, gene flow, and natural selection on genes within and among populations

mutation is the _____ source of genetic variation

ultimate

point mutation

a change in a single nucleotide, often happens during DNA replication

what are the ONLY mutations that can be passed onto the next generation?

mutations in germ cells (sperm and eggs)

mutation rate in humans

10-8 per nucleotide site per generation (probability of one change to genes in individuals from each generation)

other kinds of mutations

small insertions or deletions of stretches of DNA; chromosomal mutations (chromosomes are lost, rearranged, or duplicated); whole genome duplication (plants)

since mutation rates are low, they typically have a ____ effect on allele frequencies

negligible

directional selection

selection in favor of one end of the extreme

stabilizing selection

selection in favor of intermediate/moderate traits

disruptive selection

selection in favor of both forms of extreme traits

positive directional selection

occurs when one allele results in higher rates of survival or reproduction; eventually leads to fixation of advantageous allele; allele controls for an extreme phenotypic trait

purifying selection

occurs when selection eliminates harmful alleles; harmful alleles created by mutation are eliminated by mutation

balancing selection

heterozygotes have higher fitness than either homozygote; sickle cell anemia; not the same as stabilizing selection

four important facts about genetic drift

drift’s impact is greater in small populations, allele frequencies change at random (may go up or down), drift leads to loss of genetic variation overtime, and drift can cause harmful alleles to become fixed in a population

bottleneck event

reduction in size of existing population

founder event

the estab. of a new population of smaller size

sexual selection

a form of selection in which individuals with particular inherited characteristics are more likely than other individuals to acquire mates

what drives the differences between sexes?

unequal investment in gamete production; sperm are small and easy to produce, while eggs are large and filled with nutrients

Bateman’s Principle

variation in reproductive success is greater among males than among females; male reproductive success limited by number of matings with females, female reproductive success limited by number of offspring she can produce

females are a _____ resource of reproduction

limiting

intra-sexual selection

competition among individuals of one sex

inter-sexual selection

mate choice by the opposite sex

Fisher’s “runaway” model

females prefer males with extreme traits, giving rise to sons with extreme traits and daughters with preferences for males with extreme traits

“Good genes” model

females prefer mates with certain traits because these traits are associated with higher fitness

sexual dimorphism

the systematic difference in form, size, color, or structure between males and females of the same species, often driven by sexual selection and evolutionary pressures

polytomies

indicate unresolved relationships in phylogenetic trees

sister taxa

each other’s closest relatives

where are common ancestors in phylogenetic trees?

at nodes joining branches

info. contained in phylogenetic trees

the branching pattern indicates ancestry and sometimes the branch lengths represent time

phylogenetic system of classification

taxonomy reflects degrees of relatedness

monophyletic trees

a group that contains an ancestral species and all of its descendants; mammals are monophyletic; aka clades or phylogenetic classification system

paraphyletic

a group that contains an ancestral species and some but not all of its descendants; reptiles

polyphyletic

a group that contains distantly related species but not their most recent common ancestor; “marine mammals” is polyphyletic, contains distantly related species like whales, manatees, and seals

shared ancestral characters

found in distant common ancestor and present in descendants

parsimony

tree with the fewest number of changes possible

the molecular clock

in the absence of selection, the rate of evolution of DNA sequences is equal to the mutation rate; roughly constant over time

K

rate of DNA sequence evolution (same thing as rate of fixation)

Mu

mutation rate per gamete per generation

N

population size

2N

number of gene copies in a diploid population of N individuals

1/2N

frequency of a new mutation, which is also its probability of fixation

Lynn Margulis

endosymbiosis hypothesis for the origin of eukaryotes and mitochondria/chloroplasts

endosymbiont theory

eukaryotic organelles originated from small prokaryotes that begin living in larger cells

evidence for endosymbiont theory

mitochondria and chloroplasts are superficially like bacteria, have cellular machinery to transcribe and translate DNA into proteins, replication machinery resembles prokaryotes, and organelle ribosomes are similar to prokaryotes

Biological Species Concept (BSC)

species are groups of actually or potentially interbreeding organisms that are reproductively isolated from other such groups; members of other species don’t interbreed under natural conditions