Lecture 4 - Evolution and Speciation Quiz

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Questions and Answers

What is meant by genetic drift in the context of demes?

It refers to the intentional selection of specific alleles by humans.

It is the exchange of genetic material between different species.

It is the random change in allele frequency due to sampling error. (correct)

It describes the uniform distribution of alleles in a population.

How did the Cit+ strain evolve to utilize citrate in aerobic conditions?

By duplicating the gene encoding citrate transporter expression. (correct)

By randomly integrating citrate genes from the environment.

By acquiring a new gene from a different species.

Through a mutation that permanently activated aeration genes.

What is gene flow?

The genetic variation caused by mutations in a population.

The evolution of traits due to environmental changes.

The natural selection acting on a population.

The movement of alleles between previously separate populations. (correct)

What occurred in the Long Term Evolution Experiment (LTEE) studied by Richard Lenski?

E.coli adapted to use citrate as a carbon source under aerobic conditions. Signup and view all the answers

What advantage did the Cit+ strains have in the LTEE?

They could efficiently utilize both citrate and glucose as energy sources. Signup and view all the answers

What was a significant finding about DNA repair rates in the LTEE?

Repair rates increased leading to a mutator phenotype. Signup and view all the answers

Why does selective and reproductive isolation affect genetic variation?

It prevents gene flow between different populations, maintaining distinct allele frequencies. Signup and view all the answers

What happens to alleles during the sampling process described in genetic studies?

Some alleles may become fixed while others get lost. Signup and view all the answers

What was the main effect of the drought on the Geospiza Fortis population?

Larger and harder seeds led to birds with bigger beaks surviving. Signup and view all the answers

Which of the following best describes genetic drift?

A random change in allele frequencies within a population over generations. Signup and view all the answers

What is meant by the phrase 'survival of the fittest' in the context of natural selection?

Individuals that reproduce the most successfully have the most fitness. Signup and view all the answers

Which postulate indicates that certain traits are passed from one generation to the next?

Postulate 2: Heritability of variation. Signup and view all the answers

Which statement about mutations is accurate?

Mutations can change allele frequencies even when not affecting phenotype. Signup and view all the answers

Which of the following mechanisms is NOT a main mechanism of evolution?

Phenotypic variation Signup and view all the answers

In the study of the medium ground finch, what was observed about the relationship between midbeak depth and offspring?

Midbeak depth showed a clear correlation between parents and offspring. Signup and view all the answers

How do mutations function in the context of evolution?

They can serve as raw material for natural selection. Signup and view all the answers

What was the primary observation made by Rosemary and Grant (1976-1978) on Geospiza fortis finches?

The drought led to natural selection favoring deeper, stronger beaks. Signup and view all the answers

What is a key concept of Darwin’s first postulate?

Individuals within a species exhibit variation in traits. Signup and view all the answers

What happens when a mutation has no selective value?

It can still influence allele frequencies through genetic drift. Signup and view all the answers

What is the outcome of gene flow between populations?

Homogeneity by introducing new alleles into populations. Signup and view all the answers

What is an example of instant speciation in tree frogs?

Chromosomal duplication during meiosis, creating Hyla versicolor. Signup and view all the answers

How does genetic drift affect allele frequencies?

Through random sampling errors over successive generations. Signup and view all the answers

What defines a eukaryotic species?

Organisms capable of interbreeding to produce viable, fertile offspring. Signup and view all the answers

What happens to recessive advantageous alleles in a population?

They take longer to spread compared to dominant advantageous alleles. Signup and view all the answers

What is the primary driver of speciation?

Selective and reproductive isolation. Signup and view all the answers

How can gene flow reduce genetic variation between populations?

By introducing new alleles that create homogeneity. Signup and view all the answers

What characteristic allowed Cit+ strains of E. coli in Lenski’s experiment to use citrate in aerobic conditions?

Duplicated gene encoding citrate transporter expression. Signup and view all the answers

What is the outcome of selective and reproductive isolation between populations?

Speciation and increased genetic diversity. Signup and view all the answers

Which factor is a direct result of chromosomal duplication in tree frogs?

Formation of a new species, Hyla versicolor. Signup and view all the answers

What best describes natural selection?

Survival and reproduction of individuals with advantageous traits. Signup and view all the answers

How do advantageous recessive alleles spread in a population?

They require homozygotes to accumulate, taking longer to spread. Signup and view all the answers

What does "fitness" mean in evolutionary terms?

The ability of an individual to survive and reproduce. Signup and view all the answers

What does reproductive isolation achieve in eukaryotic species?

Ensures populations cannot interbreed with other species. Signup and view all the answers

Which mechanism does NOT directly lead to speciation?

Gene flow Signup and view all the answers

Why are mutations described as the "raw materials" of evolution?

They provide genetic variation for selection and drift to act upon. Signup and view all the answers

Study Notes

Evolution and Speciation

Three main mechanisms drive evolution: natural selection, genetic drift, and gene flow.

Darwin's Postulates

Rosemary and Grant (1976-78) studied the medium ground finch (Geospiza Fortis) observing beak shape variation.
Their data shows a correlation between midparent beak depth and offspring beak depth.
In 1978, despite a significant population decrease due to drought, the relationship between parent and offspring beak depth remained consistent.

1976 Drought Impact

A 1976 drought reduced seed availability, favoring larger, harder seeds.
This led to a decrease in the finch population and an increase in average beak depth.

1978 Finch Population Recovery

In 1978, only 90 finches survived the drought.
The population mean beak depth increased, indicating selection for birds with larger, stronger beaks.
This natural selection was driven by the change in available food sources and the relationship between birds and their beaks.

Darwin's Postulates, Explained

Postulate 1: Individuals within a species are variable. Traits, such as beak shapes—hard, shallow, or small—vary.
Postulate 2: Some of this variation is heritable; offspring inherit traits from their parents.
Postulate 3: Reproduction is not random. Certain traits allow survival and reproduction better under specific environmental conditions.

Genetic Drift

Genetic drift occurs, even without natural selection, because not all sperm and eggs contribute to the next generation. This creates a sampling error.
A sample of sperm or eggs may over-represent one allele (fixed) or under-represent another in the next generation.

Natural Selection and Allele Fixation

Dominant advantageous alleles are quickly noticeable in both heterozygotes and homozygotes, rapidly increasing in frequency.
Recessive advantageous alleles take longer to become noticeable because they only appear in homozygotes and take time to reach the appropriate frequencies.

Long-Term Evolution Experiment (LTEE)

Richard Lenski's experiment with E. coli illustrated evolution and adaptation.
Starting with 12 identical E. coli populations, researchers observed increased growth rates and DNA repair mechanisms.
In some populations, the E.coli developed the capacity to utilize citrate under aerobic conditions, a phenotypic shift not previously possible.

Gene Flow

Gene flow is the movement of alleles between populations.
This can occur via migration of adults or gametes.
Factors like genetic drift, gene flow, and selective isolation influence biodiversity and speciation.

Speciation

A species is a group of organisms capable of interbreeding and producing fertile offspring.
Eukaryotic species are reproductively isolated, preventing offspring with other species.
Factors like genetic drift, gene flow, and selective isolation can lead to diversification and speciation.
In the specific case of tree frogs, chromosomal duplication during meiosis can trigger instant speciation.

Citrate Metabolism

E. coli in aerobic conditions do not typically utilize citrate as a carbon source.
Certain populations developed a duplicate citrate transporter gene, allowing them to utilize citrate and leading to higher fitness rates in these populations.

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Description

Test your understanding of the mechanisms of evolution, including natural selection and genetic drift, through the study of the medium ground finch. Delve into the research by Rosemary and Grant and explore how environmental changes impact species adaptation and survival. This quiz covers key concepts from evolution and speciation.