bio 1b - ecology unit

what is the evidence that life on earth descended from a single common ancestor?

- Similarity of form (of individual groups)

what are the 3 domains of life

Bacteria, Archaea, Eukarya

what is archaea?

single celled prokaryotes that often live in Earth's extreme environments

What is bacteria?

single celled organism that live in many environments. (can be beneficial or pathogenic)

What are eukaryotes?

basically everything else -> single celled organisms, plants, animals, fungi

Eukaryotic cells

Contain a nucleus and other organelles that are bound by membranes.

prokaryotic cells

cells without a nucleus or other membrane-bound organelles

What unites Archaea and Eukaryotes?

Components of DNA replication, transcription and translation; More than 30 ribosomal proteins shared between archaea and eukaryotes but absent in bacteria; Translation factors; RNA polymerases more similar between archaea and eukaryotes

logic of evolution

descent with modification

Change in the genetic composition of a population between generations

Earth's species are descendants of ancestral species that were different from the present day species

4 attributes necessary for natural selection

1. Variation: members of a population must have different, heritable traits

2. Overproduction/struggle for existence: all species can produce more offspring than their environment can support, creates competition for limited resources

3. Heritability: members whose inherited traits give them a higher probability of surviving tend to leave more offspring than others

4. Unequal survival: members with traits better suited for the environment will lead to the accumulation of those beneficial traits for the next generations

why are the 4 attributes for natural selection necessary?

- Without variation, all members would be genetically identical -> equally susceptible or resistant to environmental pressures -> vulnerable for extinction

- If traits aren't heritable then any advantages variations cant accumulate over time

- Not all individuals can survive and reproduce to their full potential (differential success is the actual mechanism of "selection")

No genetic difference, no advantageous shift

understand the key ideas that gave rise to the idea of evolution proposed by darwin and wallace

Early views: Aristotle thought species were fixed (scala naturae).

Classification: Linnaeus created binomial naming and showed life as a nested hierarchy, hinting at relatedness (but did not accept evolution).

Fossils: Cuvier showed that older rock layers contain fossils unlike modern species → life changes over time.

Geology: Hutton & Lyell proposed uniformitarianism (slow, continuous processes; Earth is very old), allowing time for gradual biological change.

Early evolution: Lamarck proposed species change (mechanism wrong), but recognized adaptation; Erasmus Darwin suggested common ancestry.

Population pressure: Malthus showed populations outgrow resources → struggle for existence.

Evidence that Darwin gathered to support evolution by natural selection

- Biogeography (Galapagos Islands): Darwin observed that finches and other animals on the Galapagos Islands were similar to species on the nearby Ecuadorian mainland but varied from island to island, suggesting they adapted to local environments.

- Fossil Record (Paleontology): He noted that fossils in South America, such as the armadillo-like Glyptodon, shared similarities with living species, indicating a lineage of descent with modification over time.

- Comparative Anatomy & Homology: Darwin identified similar skeletal structures (e.g., forelimbs in humans, bats, and whales) that served different functions but indicated a common ancestor, as well as vestigial,, non-functional structures.

- Artificial Selection (Breeding): Darwin studied domesticated plants and animals, noting how human-driven selective breeding could produce dramatic changes in a short time, which supported the potential for natural, environmental selection.

describe the assumptions of the hardy weinberg model and why each is important

No mutation: no new alleles are introduced, and existing alleles don't change

- Why is it important: mutations are the ultimate source of genetic variation, without this rule, the "gene pool" size and composition would constantly shift

Random mating: every individual has an equal chance of mating with any other individual of the opposite sex

- Why is it important: non random mating (like inbreeding) changes genotype frequencies, even if allele frequencies stay the same

No gene flow: the population is closed; no individuals migrate in or out

- Why is it important: immigration or emigration introduces or removes alleles, which directly alters the frequency of the local gene pool

Infinite population size: the population is large enough that random chance does not affect inheritance

- Why is it important: in small populations, genetic drift can cause alleles to disappear or become fixed purely by luck, regardless of how "fit" they are

No natural selection: all genotypes have equal chances of survival and reproduction

- Why is it important: selection favors specific traits, causing "advantageous" alleles to increase in frequency over time

what are the three mechanisms that alter allele frequencies?

natural selection: results in alleles being passed to the next generation in proportions that differ from those in the present generation

- can cause adaptive evolution: results in a better match between organisms and their environment

genetic drift: chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next (especially in small populations)

- Ongoing genetic drift is likely to have substantial effects on the gene pool until the population becomes large enough that chance events have less impact

gene flow: transfer of alleles into or out of a population due to the movement of fertile individuals or gametes (REDUCES genetic difference BETWEEN POPULATIONS)

founder effect (genetic drift)

the establishment of a new population in a smaller size

bottleneck effect (genetic drift)

a sudden reduction in population size due to a change in the environment

directional selection

conditions favor individuals exhibiting ONE extreme of a phenotypic range -> shifts a frequency curve for that side

disruptive selection

favors individuals at both extremes of the phenotypic range

stabilizing selection

Natural selection that favors intermediate variants by acting against extreme phenotypes

positive directional selection

favors a single allele that increases fitness, shifting the phenotype distribution toward one extreme (often leads to allele fixation)

purifying selection (negative selection)

removes deleterious (damaging) alleles from a population; common form of stabilizing selection

balancing selection

maintains multiple, different alleles at stable frequencies (occurs through heterozygote advantage - they have higher fitness than either homozygote)

-> prevents any single allele from becoming fixed or lost, holding frequencies at an intermediate equilibrium

paternal age effect

As a man ages, mutations can accumulate in the stem cells that form the sperm. Older men are more likely to produce gametes with genetic errors that lead to dominant single gene diseases.

Microevolution vs. Macroevolution

Microevolution happens on a small scale (within a single population), while macroevolution is large-scale changes that occur over long periods (leads to the emergence of new species)

allele frequencies

Proportion of different alleles in a population.

genetic variation

diversity in DNA sequences within a population = differences in phenotype

adaptation

inherited characteristic that increases an organism's chance of survival

Speciation

single ancestor splits into genetically different species

Phenotype

physical characteristics/observable traits of an organism

Genotype

An organism's genetic makeup, or allele combinations.

recessive alleles

an allele that produces its characteristic phenotype only when its paired allele is identical

homozygous

An organism that has two identical alleles for a trait

heterozygous

An organism that has two different alleles for a trait

genotype frequencies

Proportions of different genotypes in a population.

population genetics

Study of allele frequency distribution and change under the influence of evolutionary processes.

inbreeding

Continued breeding of individuals with similar characteristics

non-random mating

mating between individuals of the same phenotype or by those who live nearby

random mating

Mating between individuals where the choice of partner is not influenced by the genotypes

sister taxa

Groups of organisms that share an immediate common ancestor and hence are each other's closest relatives.

Polytomy (phylogenetic tree)

a branch point from which more than two descendant groups emerge

key points about phylogenetic trees

1. Intended to show patterns of descent, NOT PHENOTYPIC SIMILARITY

2. sequence of branching in a tree does not necessarily indicate the actual ages of the particular species

3. we should not assume that a taxon on a phylogenetic tree evolved from the taxon next to it

monophyletic

consists of an ancestral species and all of its descendants

paraphyletic

consists of an ancestral species and SOME, but not all, of its descendants

- **most recent common ancestor of all members of the group IS PART OF THE GROUP

polyphyletic

includes distantly related species but does not include their most common ancestor

- ***most recent common ancestor IS NOT PART OF THE GROUP

Homologies

phenotypic and genetic similarities due to shared ancestry

Analogies

Similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages

explain how characters (both phenotypic and genotypic) are used to uncover phylogenetic relationships

homologies, analogies, fossil records and examination of DNA, genes (if two or more organisms share many portions of their nucleotide sequences, it is likely that the genes are homologous)

cladistics

classification based on common ancestry

sexual selection

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