Exam 1

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Last updated 6:48 PM on 9/3/25
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52 Terms

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Anagenesis

gradual evolution of a species into a new form without branching. The original species transforms into a new one

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Cladogenesis

splitting of a lineage into two or more separate species. It increases biodiversity as new branches form on the tree of life

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morphospecies

defined based on physical features like shape, size, and structure, rather than genetic or reproductive data

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biological species concept

group of interbreeding organisms that can produce fertile offspring and are reproductively isolated from other such groups

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limitations of the biological species concept

  • Doesn’t apply to asexual organisms (e.g., bacteria).

  • Not useful for fossils, where reproductive behavior can’t be observed.

  • Difficult to apply in hybrid zones where gene flow occurs.

  • Assumes reproductive isolation, which isn’t always clear-cut.

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Prezygotic isolation

Prevents fertilization from occurring

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Postzygotic isolation

Occurs after fertilization, affecting the viability or fertility of the offspring

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Geographic isolation

physical barriers (e.g., mountains, rivers) separate populations

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Habitat isolation

Species live in the same area but occupy different habitats

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Behavioral isolation

Differences in mating behaviors prevent mating

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Temporal isolation

Species breed at different times (day, season, or year)

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Mechanical isolation

Incompatible reproductive structures prevent mating

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Gametic isolation

Gametes (sperm and egg) are incompatible and cannot fuse

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Reduced hybrid viability

Offspring fail to develop properly or die early

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Reduced hybrid fertility

Offspring are sterile (e.g., mule)

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Hybrid breakdown

First-generation hybrids are fertile, but their offspring are weak or sterile

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Adaptive radiation

rapid evolution of multiple species from a common ancestor, often when new habitats or ecological niches become available. Example: Darwin’s finches

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Allopatric speciation

when a population is geographically isolated, leading to genetic divergence due to mutation, natural selection, and drift. Over time, the separated populations become distinct species.

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Sympatric speciation

occurs without geographic isolation

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Polyploidy

causes instant reproductive isolation by doubling the number of chromosomes, making the new polyploid incompatible with the original population

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Autopolyploidy

Chromosome duplication within a single species

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Allopolyploidy

chromosome duplication that occurs after hybridization between two different species

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Gradualism

Evolution occurs slowly and steadily over time

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Punctuated equilibrium

Long periods of stability are interrupted by rapid bursts of change, often due to environmental shifts or new niches

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hybrid zone

region where two species meet and mate, producing hybrids.
Factors that prevent gene flow include:

  • Strong selection against hybrids

  • Ecological differences between parental species

  • Reinforcement of reproductive barriers

  • Reduced hybrid viability or fertility

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Speciation

the process where one species splits into two or more new species

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Microevolution

Small changes in a population’s gene pool over time (like changes in allele frequency)

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What characteristics do biologists use to classify organisms into species?

  • Morphology (body shape & size),

  • Physiology (body functions),

  • Biochemistry (chemical makeup)

  • DNA sequences to classify organisms

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Why did Darwin call the origin of species the “mystery of mysteries”?

he was fascinated by how new life forms first appeared on Earth

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What is an example of a species unique to the Galápagos Islands?

The Galápagos giant tortoise

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What does evolutionary theory try to explain?

How new species form and how populations change over time

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Can gene flow occur between different species? Give an example

Yes, like grizzly bears and polar bears producing “grolar bears.”

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What determines some phenotypic differences in organisms?

Some phenotypic differences are determined by a single gene pair with clear "either-or" outcomes (e.g., flower color).

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What is polygenic variation?

Phenotypic differences that result from the influence of two or more gene pairs and vary along a continuum in a population (e.g., human height).

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How is genetic variation measured?

Genetic variation can be measured by gene variability (heterozygosity) and nucleotide variability (DNA sequence differences between individuals).

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What is heterozygosity in a population?

Heterozygosity measures the average percentage of gene loci in a population that are heterozygous (have two different alleles)

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where does most nucleotide variation occur?

Most nucleotide variation occurs in noncoding regions (introns), which do not affect protein function

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What causes non-genetic phenotypic variation?

Non-genetic variation is caused by environmental factors (e.g., diet, climate) and does not lead to evolutionary changes.

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What is the only type of variation that has evolutionary consequences?

Genetic variation is the only type that can be passed down to offspring and lead to evolution

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What are the sources of genetic variation?

Genetic variation arises through mutation and sexual reproduction (genetic recombination)

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How do mutations contribute to genetic variation?

Mutations change the DNA sequence, creating new alleles. Only mutations in gametes (sperm or eggs) are passed on to offspring

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What is a point mutation?

A point mutation is a change in a single nucleotide in the DNA sequence, which can create new alleles

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What are the possible effects of a point mutation?

can be harmful, beneficial, or have no effect. Harmful mutations can be hidden if recessive, while beneficial mutations are rare.

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What three big ideas about life do lepidopterans (like moths and butterflies) illustrate?

1. Adaptation to the environment
2. Unity of life (shared traits)
3. Diversity of life (many species

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What was Georges Cuvier’s idea about fossils and rock layers (strata)?

He believed catastrophes wiped out species and new ones came in from other areas (catastrophism).

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What idea did Hutton and Lyell propose about how Earth changes?

Changes happen slowly over time through continuous processes (geological gradualism)

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What did Lamarck believe about how species evolve?

That traits gained during life could be passed to offspring (use/disuse theory), but this idea is incorrect

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Why is Lamarck’s theory of acquired traits not accepted today?

Because acquired traits (like muscle from exercise) are not passed to offspring genetically

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What were Darwin’s early studies and career path?

He studied medicine (quit), theology (graduated), and became a naturalist on the HMS Beagle.

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What did Darwin observe on his voyage that influenced his thinking?

Fossils similar to living species, species variation by region, and an earthquake showing land changes.

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How did an earthquake in Chile affect Darwin’s thinking?

It showed him that Earth’s surface can change gradually, supporting gradualism

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What did Darwin notice about animals on the Galápagos Islands?

Each island had different species that likely evolved from South American ancestors