Diversity of Life

Biology 103 Instructor: Jim Driver

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Course Business

     Instructor: Jim Driver ([email protected]) Required text: Biology, Campbell and Reese, 7 th edition Diversity of Life is a continuation of Principles of Biology A comprehensive syllabus and lecture schedule will be provided This course will have four exams, one will be a take home

Course Business

   Classroom attendance is STRONGLY recommended Taking clear, concise lectures notes will help in this and future university classes Exam questions will come from the lecture notes. Use the textbook to better understand the materials covered in lecture, BUT……a thorough reading of the text will help in the future and may be enjoyable!

How to study for my exams

• • • • • Come to class Take notes, pay attention to emphasis on topics or concepts Use textbook to better understand notes Know all terms in notes If you have questions - ask during class or come see me during office hours

Yes, life sure is diverse!

Diversity of Life – Course Preview

  Biology of Life covered molecular biology, cell biology, and genetics. This course covers the rest!

But seriously, topics we will cover include:  How did life develop such diversity from its initial beginnings?

   How is life categorized?

What are the hallmarks of the major life groupings?

How does life interact on a local, regional, and planetary level?

The molecular structure of DNA • Holds all the information to make a complex organism in 4 bases!

Nucleus DNA

Figure 1.7

Cell Nucleotide A C T A T A C C G T A G T A

(a) DNA double helix.

This model shows each atom in a segment of DNA.Made up of two long chains of building blocks called nucleotides, a DNA molecule takes the three-dimensional form of a double helix.

(b) Single strand of DNA.

These geometric shapes and letters are simple symbols for the nucleotides in a small section of one chain of a DNA molecule. Genetic information is encoded in specific sequences of the four types of nucleotides (their names are abbreviated here as A, T, C, and G).

Diversity and Relationships • Carolus Linnaeus – taxonomy – How can we put all the organisms in the right boxes?

– Developed binomial nomenclature (

Genus species)

– He classified similar species (by morphology) into increasingly general categories

What is common thread in each grouping?

Evolution and Diversity

• Evolution accounts for life’s unity and diversity

Darwin and “descent with modification” • Lamark’s theory of evolution – Use and disuse – Inheritance of acquired characteristics – Based on improvement of the individual during its life and transmission of the improvements to offspring

What Lamarck thought…

Darwinian Evolution • 1859 – On The Origin of Species By Means of Natural Selection (Alfred Russel Wallace also had same idea) – 2 main ideas • Evolution explains life’s unity and diversity • Natural selection is a cause of adaptive evolution • Remember: – Individuals survive and reproduce – Populations evolve and adapt

Variation driven by random mutation and sexual recombination

Overproduction

Reproductive success Imagine an alternative scenario

How did Darwin get to natural selection?

Observations and inferences.

• Obs. #1 – all species have great potential fertility • #2 – populations tend to remain stable • #3 – resources are limited • Inference #1 – overproduction leads to struggle for existence • Obs. #4 – in a population, no two individuals are alike • #5 variation is heritable • Inf. #2 – individuals with inherited traits that best fit the environment will likely leave more offspring • Inf. #3 – unequal survival and reproduction will lead to gradual change in a population, with favorable characteristics accumulating over the generations

In other words….

• Natural selection is: – differential success in reproduction – an interaction between the environment and the variability in individuals making up the population • Natural selection leads to the adaptation of a population of organisms to their environment

Evidence for natural selection

• Antibiotic resistance in bacteria – Bacterial populations are not always clonal – Mutations in DNA during replication can lead to protein structure changes • Moth coloration in England – Pollution caused change in tree bark color – Some moths stood out leading to differential predation, changing population • Pesticide resistance in insect populations • Toxins in Newts

Figure 22.12

The fittest survive and reproduce

Understand:

• Fitness –any heritable trait that increases relative reproductive success – Strictly dependent on the specific environment • Adaptation – refers to populations adapting to the environment, not the individual • Scientific Theory – useful, comprehensive, and well-supported explanation for a wide range of observations

Understand:

• Fitness –any heritable trait that increases relative reproductive success – Strictly dependent on the specific environment • Adaptation – refers to populations adapting to the environment, not the individual • Scientific Theory – useful, comprehensive, and well-supported explanation for a wide range of observations • Evolution in its strict meaning is a change in allele frequencies in a population over time…….But……

Evolution – change through time

Macroevolution Speciation Microevolution

Definitions

• Microevolution – change in allele frequencies in population over time – Alleles - alternative versions of a gene that produce distinguishable phenotypic effects • Speciation – a population’s genetic divergence leads to reproductive isolation • Macroevolution – the level of change of life on the planet observed over geological time

Understanding Evolution • Evidence indicates that all life on this planet is related. Eg. DNA-based • Later forms show a relationship to earlier forms based on common characteristics • Natural selection provides a mechanism to explain how these changes came about • Natural selection requires heritable variation in populations and conditions that favor one variant over another

Evidence for evolution • Descent with modification can explain similarities in structures with different functions (homology) • Anatomical homologies

Evidence of evolution • Descent with modification can explain similarities in structures with different functions (homology) • Anatomical homologies • Molecular homologies

Biogeography

• The geographic distribution of species • Closely related species inhabit same geographic region (common evolution) • But: – Same ecological niches in distant regions can be occupied by evolutionarily different species

Biogeography

• The geographic distribution of species • Closely related species inhabit the same geographic region • But: these ecological niches in distant regions can be occupied by evolutionarily different species • Darwin observed that many species are endemic

Evolution of Populations Chapter 23

Population genetics

• How do populations change (genetically) over time?

• Gene pool – total of all genes in a population • Alleles – alternative forms of a gene – Remember in sexual spp. One gene from mom, one from dad

Mendelian Genetics Review

Mechanisms of Variation • Mutations – changes in nucleotide sequence of DNA – Only mutations gametes passed to offspring – Point mutations - single base change – Chromosomal mutations - large scale deletions, disruptions or rearrangements • Also gene duplication (eg detecting odors) – Mutation rates usually low in animals but much higher in prokaryotes (eg. HIV)

Mechanisms of Variation • Sexual recombination – Rearranges alleles into new combinations each generation (review Chap. 13) – Remember, one chromosome of each pair from each parent – Do bacteria have sex? YES!

• What does THAT look like?

Sexual reproduction • Two parents give rise to offspring that have unique combinations of genes inherited from the two parents

Crossing Over

(Not on Exam) –

Produces recombinant chromosomes with genes derived from two different parents

Prophase I of meiosis Nonsister chromatids Tetrad Chiasma, site of crossing over Metaphase I

Figure 13.11

Metaphase II Daughter cells Recombinant chromosomes

Also Independent Assortment (not on exam) –

Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs Key

Maternal set of chromosomes Paternal set of chromosomes

Possibility 1 Possibility 2

Two equally probable arrangements of chromosomes at metaphase I Metaphase II

Figure 13.10

Combination 1 Combination 2 Daughter cells Combination 3 Combination 4

How populations change

• Natural selection – Variants better suited to the environment tend to produce more offspring • Or → Genetic drift – population changes unexpectedly

Genetic drift – unpredictable changes

How populations change

• Genetic drift can come about through: • Bottleneck effect; a few survivors • Founder Effect – A few individuals form an isolated population

How populations change

• Gene Flow – Movement of fertile individuals or gametes (eg. Pollen) into or out of a population • Egs, pollen, storms or tsunami’s etc.

– Think humans and travel

Adaptive Evolution and Variation • Genetic Variation can be: – Discrete characters (either/or) – Quantitative characters (vary along continuum) • Measuring variation – Average heterozygosity (eg. Fruit flies 1800 out of 13,000 gene loci,) – Nucleotide variability, in humans ~0.1% of DNA bases

Variation between populations: - Geographic variation in a species can follow a cline (variation in trait that parallels environmental gradient)

Fitness

• • •

– contribution individual makes to gene pool of next generation Relative fitness – contribution of one genotype compared to alternative at same locus based on reproductive success ONLY

How does natural selection work?

• Directional selection – Favors extremes at one end of distribution

Modes of selection

Natural Selection, again • Disruptive selection – Favors extremes at both ends of distribution

Modes of selection

Natural Selection, again • Stabilizing selection – Removes extremes and favors intermediates (most common type)

Modes of selection

Preserving variation

• Most eukaryotes are diploid (2 copies of each chromosome/gene) • Homozygous – identical genes at a location • Heterozygous – different genes • Heterozygote advantage – sickle cell anemia

How is it preserved?

• Wouldn’t natural selection remove all unfavorable genotypes?

• No, due to: – Recessive alleles – Heterozygote advantage (eg sickle cell) – Neutral variation (really neutral?)

Hardy-Weinberg Theorem • Used to model non-evolving gene pools • Can be used to determine allele frequencies within a population – Or, what is happening to variation in a population • What is H-W good for?

H-W Theorem • - frequencies of alleles and genotypes in gene pool remains constant from generation to generation if only Mendelian segregation and recombination of alleles happens • Requires: – Extremely large population size – No gene flow – No mutations – Random mating – No natural selection

H-W and Sickle cell anemia (no math on exam) • Eg. In some populations the sickle cell allele is 20% of all hemoglobin alleles • H-W p 2 + 2pq + q 2 = 1 p = normal hemoglobin (0.8 of population) q = mutant hemoglobin (0.2 of population) p 2 = (0.8)(0.8) = 0.64 or 64% of population q 2 = (0.2)(0.2) = 0.04 or 4% population 2pq = 2(0.8)(0.2) = 0.32 or 32% of population

What if?

• Malaria eradicated – Change in natural selection?

– Loss of heterozygote advantage?

– Increase in gene flow?

Sexual selection

• Why sex anyway?

– Lower reproduction rate than asexual – Provides variation for future selection/adaptation – Can provide short-term variation for disease resistance

Sexual selection can lead to differences between sexes

Sexual Dimorphism

• If sexual characteristics increase mating success then benefit outweighs risk – “showy alleles” increase – Egs. Horns, coloration, displays

The Evolution of Perfect Organisms: Why doesn’t it happen?

• What is perfect?

• Evolution is limited by historical constraints • Adaptations are often compromises • Chance and natural selection interact • Selection can only edit existing variation