Evolution Chapters 22, 23, 24, 25 and 26

Essence of Darwin’s Ideas Natural selection heritable variation exists in populations over-production of offspring more offspring than the environment can support competition for food, mates, nesting sites, escape predators differential survival successful traits = adaptations differential reproduction adaptations become more common in population

Evidence for Evolution Paleontology – fossils show change in a species over time Biogeography – Similar species are found in similar ecosystems around the world Morphology – Comparing structures Homologous structures – body parts with similar structure but possible different function. Shows common ancestry Analogous structures – similar structure develops in organisms that share a common ecosystem but not a common ancestry Biochemical or Molecular - Similarities in gene sequences, proteins, DNA

How old is that fossil? Relative Dating Absolute Dating Age of fossils based according to their location in strata Absolute Dating Age of fossils determined by analyzing the content of radioactive isotopes found in the fossil. Half-life: The length of time required for half of the radioactive elements to change into another stable element.

Layers of deposited sediment Younger stratum with more recent fossils Figure 22.3 Formation of sedimentary strata with fossils Older stratum with older fossils

Homologous Structures

Analogous Structures

Comparative hemoglobin structure Molecular Homology The sequence in DNA & proteins is a molecular record of evolutionary relationships. Why compare DNA & proteins across species? 10 20 30 40 50 60 70 80 90 100 110 120 Lamprey Frog Bird Dog Macaque Human 32 8 45 67 125 Comparative hemoglobin structure Molecular Record What are we comparing here? - comparing DNA (base sequence) & proteins (amino acid sequence) What assumption do we make about genes and relatedness?  the more closely related, the more DNA bases & amino acids you have in common have to compare genes for protein the organisms have in common… can’t compare genes for proteins you don’t have Number of amino acid differences between hemoglobin (146 aa) of vertebrate species and that of humans

Evolution evidence at the cellular level Domains: Archaea, Bacteria and Eukarya Elements conserved through all: DNA, RNA and many metabolic pathways. Eukaryotes – core features: Cytoskeleton Nucleus Membrane-bound organelles Linear chromosomes Endomembrane system

How do genetic variations occur? What is Evolution? Change in the genetic makeup of a population over time. Fitness – those with favorable variations for survival and reproduction. Populations can evolve, not individuals. Diverse gene pool good for long-term survival of a species. Genetic variations are important! How do genetic variations occur?

Where does Variation come from? Mutation random changes to DNA errors in mitosis & meiosis environmental damage Sexual reproduction mixing of alleles genetic recombination new arrangements of alleles in every offspring new combinations = new phenotypes

Natural Selection Major mechanism of evolution Environment is always changing Acts upon the phenotype of the population Based on Darwin’s idea that resources are limited and that there is competition for those resources. Adaptation = a genetic variation favored by natural selection. When allele frequencies shift, speciation occurs Thus, the frequency change is NOT RANDOM

Populations & gene pools Concepts a population is a localized group of interbreeding individuals gene pool is collection of alleles in the population remember difference between alleles & genes! allele frequency is how common is that allele in the population how many A vs. a in whole population

Hardy-Weinberg equilibrium Hypothetical, non-evolving population preserves allele frequencies natural populations rarely in H-W equilibrium useful model to measure if forces are acting on a population measuring evolutionary change G.H. Hardy (the English mathematician) and W. Weinberg (the German physician) independently worked out the mathematical basis of population genetics in 1908. Their formula predicts the expected genotype frequencies using the allele frequencies in a diploid Mendelian population. They were concerned with questions like "what happens to the frequencies of alleles in a population over time?" and "would you expect to see alleles disappear or become more frequent over time?" G.H. Hardy mathematician W. Weinberg physician

Evolution of populations Evolution = change in allele frequencies in a population hypothetical: what conditions would cause allele frequencies to not change? very large population size (no genetic drift) no migration (no gene flow in or out) no mutation (no genetic change) random mating (no sexual selection) no natural selection (everyone is equally fit) H-W occurs ONLY in non-evolving populations!

Hardy-Weinberg theorem Frequencies are usually written as decimals! Counting Alleles assume 2 alleles = B, b frequency of dominant allele (B) = p frequency of recessive allele (b) = q frequencies must add to 1 (100%), so: p + q = 1 BB Bb bb

Hardy-Weinberg theorem Counting Individuals frequency of homozygous dominant: p x p = p2 frequency of homozygous recessive: q x q = q2 frequency of heterozygotes: (p x q) + (q x p) = 2pq frequencies of all individuals must add to 1 (100%), so: p2 + 2pq + q2 = 1 BB Bb bb

H-W formulas Alleles: p + q = 1 Individuals: p2 + 2pq + q2 = 1 B b BB

Practice Problem: In a population of 100 cats, there are 16 white ones. White fur is recessive to black. What are the frequencies of the genotypes?

Example of an evolving population: Peppered moth Variation of colors in the population existed (Black, Peppered, White) As environmental conditions changed, the frequency of the recessive allele increased. This was seen as an adaptation to the environment that allowed the species to survive and reproduce better.

In addition to natural selection, evolutionary change is also driven by random processes…

Genetic Drift Chance events changing frequency of traits in a population not adaptation to environmental conditions not selection founder effect small group splinters off & starts a new colony it’s random who joins the group bottleneck a disaster reduces population to small number & then population recovers & expands again but from a limited gene pool who survives disaster may be random Founders: When a new population is started by only a small group of individuals. Just by chance some rare alleles may be at high frequency; others may be missing; skew the gene pool of new population. Ex: human populations that started from small group of colonists example: colonization of New World Bottleneck: When large population is drastically reduced by a disaster-famine, natural disaster, loss of habitat…loss of variation by chance event alleles lost from gene pool not due to fitness, narrows the gene pool

Effects of Selection

Heterozygote Advantage Keeps the recessive allele in the population Ex: Sickle Cell Anemia aa – dies of sickle cell anemia Aa – some side affects BUT resistant to malaria! AA – no disease present BUT prone to malaria

Speciation Changes in allele frequency are so great that a new species is formed Can be slow and gradual or in “bursts” Extinction rates can be rapid and then adaptive radiation follows when new habitats are available

So… What is a species? Population whose members can interbreed & produce viable, fertile offspring Reproductively compatible Distinct species: songs & behaviors are different enough to prevent interbreeding Humans re so diverse but considered one species, whereas these Meadowlarks look so similar but are considered different species. Meadowlarks Similar body & colorations, but are distinct biological species because their songs & other behaviors are different enough to prevent interbreeding Eastern Meadowlark Western Meadowlark 26

How do new species originate? When two populations become reproductively isolated from each other. Speciation Modes: allopatric geographic separation “other country” sympatric still live in same area “same country”

Allopatric Speciation Physical/geographical separation of two populations Allele frequencies diverge After a length of time the two population are so different that they are considered different species If the barrier is removed interbreeding will still not occur due to pre/post zygotic isolation

Sympatric Speciation Formation of a new species without geographic isolation. Causes: Pre-zygotic barriers exist to mating Polyploidy (only organism with an even number of chromosomes are fertile…speciation occurs quickly) Hybridization: two different forms of a species mate in common ground (hybrid zone) and produce offspring with greater genetic diversity than the parents….eventually the hybrid diverges from both sets of parents

Sympatric Speciation Gene flow has been reduced between flies that feed on different food varieties, even though they both live in the same geographic area.

Pre-zygotic Isolation Sperm never gets a chance to meet egg Geographic isolation: barriers prevent mating Ecological isolation: different habitats in same region Temporal isolation: different populations are fertile at different times Behavior Isolation: they don’t recognize each other or the mating rituals Mechanical isolation: morphological differences Gamete Isolation: Sperm and egg do not recognize each other Sea urchins release sperm & eggs into surrounding waters where they fuse & form zygotes. Gametes of different species— red & purple —are unable to fuse.

Post-zygotic Isolation Hybrid Inviability – the embryo cannot develop inside the mothers womb Hybrid Sterility – Adult individuals can be produced BUT they are not fertile Hybrid Breakdown – each successive generation has less fertility than the parental generation Species of salamander genus, Ensatina, may interbreed, but most hybrids do not complete development & those that do are frail. Even if hybrids are vigorous they may be sterile; chromosomes of parents may differ in number or structure & meiosis in hybrids may fail to produce normal gametes Horse(64) x donkey(62) = mule (63 chromosomes) In strains of cultivated rice, hybrids are vigorous but plants in next generation are small & sterile. On path to separate species.

Evolutionary Time Scale Microevolution – changing of allele frequencies in a population over time. Macroevolution – patterns of change over geologic time. Determines phylogeny Gradualism – species are always slowly evolving Punctuated equilibrium – periods of massive evolution followed by periods with little to no evolution

Mass Extinctions At least 5 mass extinctions have occurred throughout history. Possible causes: dramatic climate changes occurring after meteorite collisions and/or continents drift into new and different configurations.

The Primitive Earth Atmosphere: All chemicals/compounds necessary are thought to have originated on earth Inorganic precursors: Water vapor Nitrogen Carbon dioxide Small amounts of hydrogen and carbon monoxide These were the monomers for forming more complex molecules. Experiments have shown that it is possible to form organic from inorganic.

Origin of Organic Molecules Water vapor Condensed liquid with complex, organic molecules Condenser Mixture of gases ("primitive atmosphere") Heated water ("ocean") Electrodes discharge sparks (lightning simulation) Water Origin of Organic Molecules Abiotic synthesis 1920 - Oparin first molecules formed by strong energy sources 1953 - Miller & Urey test hypothesis formed organic compounds amino acids adenine CH4 H2 NH3 Attempted to prove that chemical evolution could occur The experiment Used water, methane, ammonia, hydrogen sealed inside a glass container Water was heated to produce steam and sparks were generated from electrodes Water was then cooled and allowed to condense\ Experiment went on in this cycle for 1 week Results 15% of carbon was now present in the form of organic materials 13 out of 20 amino acids were present High concentrations of the base Adenine were also detected

Key Events in Origin of Life Origin of Cells (Protobionts) lipid bubbles  separate inside from outside  metabolism & reproduction Origin of Genetics RNA is likely first genetic material multiple functions: encodes information (self-replicating), enzyme, regulatory molecule, transport molecule (tRNA, mRNA) makes inheritance possible makes natural selection & evolution possible Origin of Eukaryotes endosymbiosis Life is defined partly by two properties: accurate replication and metabolism. Neither property can exist without the other. Self–replicating molecules and a metabolism–like source of the building blocks must have appeared together. How did that happen? The necessary conditions for life may have been met by protobionts, aggregates of abiotically produced molecules surrounded by a membrane or membrane–like structure. Protobionts exhibit some of the properties associated with life, including simple reproduction and metabolism, as well as the maintenance of an internal chemical environment different from that of their surroundings. Laboratory experiments demonstrate that protobionts could have formed spontaneously from abiotically produced organic compounds. For example, small membrane–bounded droplets called liposomes can form when lipids or other organic molecules are added to water.

Timeline Key events in evolutionary history of life on Earth 3.5–4.0 bya: life originated 2.7 bya: free O2 = photosynthetic bacteria 2 bya: first eukaryotes

Prokaryotic ancestor of eukaryotic cells ~2 bya First Eukaryotes Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency natural selection! nuclear envelope endoplasmic reticulum (ER) plasma membrane infolding of the plasma membrane nucleus DNA cell wall plasma membrane Prokaryotic cell Prokaryotic ancestor of eukaryotic cells Eukaryotic cell

internal membrane system 1st Endosymbiosis Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but did not digest them mutually beneficial relationship natural selection! internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral eukaryotic cell Eukaryotic cell with mitochondrion

photosynthetic bacterium chloroplast & mitochondrion Eukaryotic cell with mitochondrion 2nd Endosymbiosis Evolution of eukaryotes origin of chloroplasts engulfed photosynthetic bacteria, but did not digest them mutually beneficial relationship natural selection! photosynthetic bacterium chloroplast mitochondrion Endosymbiosis Eukaryotic cell with chloroplast & mitochondrion

Theory of Endosymbiosis Lynn Margulis Theory of Endosymbiosis Evidence structural mitochondria & chloroplasts resemble bacterial structure genetic mitochondria & chloroplasts have their own circular DNA, like bacteria functional mitochondria & chloroplasts move freely within the cell mitochondria & chloroplasts reproduce independently from the cell

Overview: Investigating the Tree of Life Phylogeny is the evolutionary history of a species or group of related species usually organized into a phylogenetic tree Phylogenetic trees and cladograms (also tree shaped) seek to arrange organisms based on common ancestry

What is the difference between a phylogenetic tree and a cladogram? In phylogenetic trees branch lengths can represent the amount of genetic change or are proportional to time In cladograms the branch lengths are usually considered to be arbitrary Phylogenetic tree – branch length based on relative genetic change in each lineage Cladogram

What evidence are phylogenetic trees and cladograms based on? Morphologies, genes, and biochemistry of living organisms Organisms with similar morphologies or DNA sequences are likely to be more closely related Must distinguish whether a similarity is the result of homology or analogy Homology is similarity due to shared ancestry Analogy is similarity due to convergent evolution (shark/dolphin)

What is evolution? Directions: Use the color images I’ve provided to brainstorm what you know about how evolution works. There are many interrelated concepts pertaining to evolution that could be associated with these images (shoot for 8-10). Record your ideas on a separate sheet of scratch paper, they will serve as our basis for class discussion.

Homework 3/13 Finish evidence for evolution worksheet(s). Complete section 5 (gel electrophoresis) of biotech packet. Review evolution of populations in notes packet and in text book (Chapter 23, pages 472-474).