Chapter 15 – Evidence for Evolution by Natural Selection
Chapter 15 – Evidence for Evolution by Natural Selection
Video Part 1 – Darwin & His Work
Historical Context – Who helped Darwin
Lamarck – Early theory. Your genes do not change.
Malthus (populations) – Idea of struggle for survival.
Lyell – Earth mass changed; ecology.
Early theory of evolution – LaMarck’s View
Traits acquired during an organism’s lifetime (like muscles from exercise, or a giraffe stretching its neck) could be passed on to offspring.
Emphasized use and disuse (traits get stronger with use, weaker if unused).
Change happens because individuals strive or adapt directly.
How does that differ from Darwin?
Traits are inherited through genetic variation that already exists in a population (not acquired during life).
Natural selection favors individuals whose inherited traits make them more fit to survive and reproduce.
Evolution happens because those individuals leave more offspring, not because they “worked for it.”
Key Differences
Lamarck = organisms change themselves and pass that change on.
Darwin = individuals don’t change, but those born with favorable traits are more likely to survive and pass them on.
Why do we now follow Darwin over LaMarck?
We know now that DNA/Genetics allows us to pass down genetic traits. Acquired characteristics cannot be passed down like tattoos in humans.
What Darwin learned from the finches:
Adapted radiation. Different food type/environment show why birds adapted or survived.
Some birds needed bigger beaks then other birds to survive, so they adapted.
Original Natural Selection Theory
Heritable variation → exists in all population.
Our production of offspring (Malthus) → Struggle for survival. Society cannot support too many species.
Competition → animals compete for food, mate, survival (from predators)
Differentiatial survival → survival of the fittest
Differentiatial reproduction → If you survive, you reproduce, and favorable traits will continue.
15.2 — Mutations, Selection, Gene Flow, Genetic Drift, Non Random Mating
Where does variation come from?
Mutations
Random Change to DNA.
Errors in mitosis and meiosis.
Environmental Damage.
Sexual Reproduction
Mixing of Alleles (Dad + Mom).
Genetic Recombination (New arrangements of alleles in every offspring).
New combinations = New Phenotypes.
Artificial Selection —
We pick and choose the trait we want to continue; essentially this is GMO.
ie. We can manipulate the mustard seed to become multiple different vegetables like cabbage, broccoli, or even cauliflower
What does it mean? Essentially whatever we enhance changes the outcome.
Selective Breeding — Searching for the raw genetic material (Variation) that is hidden in there.
Example: Olympics hosts breaded White Pigeons to look like Doves.
How does this connect to artificial selection? Because we can pick and choose the gens we want for or application.
Natural Selection in Action — Things can happen on their own.
Example: Bacteria becomes drug resistant because we use a lot of soaps that are used to fight off bacteria
Anatomical Evidence
Homologous Structures - 1 bone, 2 bones, multi bone
What does it mean? Similar Structures that point to Common Ancestry.
Common Ancestry? Yes, the same basic structures can be found in multiple different animals
Analogous Structures - “Dont be fooled by looks”
What does it mean? While multiple animals have wings, they don’t have to have common ancestry
Examples? Dragonflys, Hawks, and Bats can all fly but they are all apart of different classes.
Common Ancestry?: No, all those structures may be common, animals are all different classes. The reasoning behind this is that all these animals needed to fly to survive.
Convergent Evolution
Sugar gilders vs flying squirrels. No common ancestor despite looking similar.
What does it mean? Animals started off on different pairs but converged together and are parallel, not the same animal although they are similar.
Vestigial Structures (organs)
What does vestigial mean? Structures of things something needed in the past. Not necessary in today.
Give some examples: Wisdom Teeth
Genetic Drift – (two Types)
Genetic Drift is changes in the gene pool of a Small Population due to chance.
Bottleneck Effect
A chance event that can cause a change in allele frequency.
For example: a chance event can cause massive deaths.
National disasters
Disease.
Survival may be totally unrelated to genotype. No way to account for it. It is 100% random
Founder Effect
When a few individuals separate and colonize a new habitat. it's gene pool will often not be representative of the original population.
Occurs when a small group breaks off from a large population to start a new one. It typically carries a smaller portion of genetic diversity.
Give examples of real life bottlenecks:
Growth Population was poor extinction 10,000 years ago. So, they induced and how tough extremely similar aging.
Although:
The Larger a Population is, the Less Likely genetic drift will occur.
Non-Random Mating & Sexual Selection
Non-Random mating - AKA - Selective mating
What does this mean? Some animals may only mate with specific animals.
Examples: Snow geese→ Blue and white tend to only mate w/ each other so you ethier get blue w/ blue or white w/ white.
Sexual Selection
INTRAsexual Selection - Within one sex
Fighting for males.
Males fight other males for mates.
INTERsexual Selection - Between sexes
Mate Choice is made by the choice of females
Female choose males with impressive features.
15.3 – Evolution can be measured by change in allele frequency
Key Concepts:
Natural Selection acts on Individuals (their traits, lifetime, gender, diet).
Evolution acts on Populations.
The 5 Agents of Evolutionary Change:
Mutation: A chemical change to DNA that could lead to evolution.
Gene Flow/Migration: The movement of organisms into or out of a population.
Non-Random Mating/Sexual Selection: When males possess certain characteristics that lead to them being selected by females.
Genetic Drift: Happens mostly w/ smaller populations Ex. You have 5 flowers, and a rabbit eats specific colors, and moves somewhere to drop them off, that is genetic drift.
Natural Selection: Differential survival based on traits.
Hardy-Weinberg Equilibrium (The "No Evolution" Null Hypothesis)
For a population to not evolve (be in equilibrium), the following conditions must be met:
1. No genetic drift (very large population).
2. No gene flow (no migration in or out).
3. No mutations (no chemical change to DNA).
4. Random mating (no sexual selection).
5. No natural selection.
Hardy-Weinberg Equations:
Allele Frequency: p+q=1
p = dominant allele
q = recessive allele
Genotype Frequency: p2+2pq+q2=1
p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q2 = frequency of homozygous recessive genotype
Example: PKU Allele Frequency
PKU is a recessive disorder, so affected individuals have genotype q2.
If 1 in 10,000 people have PKU, q2=0.0001.
Therefore, q=0.0001=0.01q.
Since p+q=1, p=1−0.01=0.99p.
15.4 – Selection can be stabilizing, directional, or disruptive.
Trait Types:
Qualitative Traits: Influenced by alleles at a single locus; discrete categories (e.g., flower color).
Quantitative Traits: Influenced by alleles at multiple loci; show continuous variation (e.g., height, weight).
Locus - Position of that trait on a chromosome
Allele - Version of a trait carried on a chromosome
Models of Selection (that act on quantitative traits):
Stabilizing Selection:
Favors the average individuals.
Reduces variation in the population.
Directional Selection:
Favors individuals at one extreme of the trait distribution.
Shifts the average trait value in one direction.
Disruptive Selection:
Favors individuals at both extremes of the trait distribution.
Favors variation and can lead to two distinct phenotypes.
15.5 – Neutral Theory, Tay-Sachs, Sickle Cell, Mutations
Mutations
Nucleotide Substitution - a type of mutation where one nucleotide in the DNA sequence is replaced by another. In other words, a single “letter” in the genetic code is swapped for a different one.
A synonymous substitution is a type of nucleotide substitution where the new codon codes for the same amino acid as the original. In other words, the “letter” changes, but the protein sequence stays the same.
A non-synonymous substitution is a type of nucleotide substitution where the new codon codes for a different amino acid or a stop codon. In other words, the “letter” changes and it alters the protein sequence.
Missense: changes the amino acid and causes a different random protein to be made
Nonsense: changes the codon to a stop signal and nothing is made after that stop codon.
Insertions, Deletions, Rearrangements
An insertion is a mutation where one or more nucleotides are added into the DNA sequence.
This can shift the reading frame → A CAT BIG can become A TURN CAT BIG
A deletion is a mutation where one or more nucleotides are removed from the DNA sequence.
Like insertions, deletions can cause a frameshift, changing the protein completely if the number of nucleotides deleted is not a multiple of three. THE CAT ATE → THE AT ATE
A rearrangement is a mutation where large segments of DNA are moved, inverted, duplicated, or exchanged.
Unlike insertions/deletions, this affects larger sections of DNA rather than a single nucleotide.
Types include:
Inversion: a DNA segment is flipped.
Duplication: a segment is copied.
Translocation: a segment moves to a different chromosome.
Neutral Theory
Many mutations in populations are relatively neutral (neither beneficial nor harmful).
These neutral mutations can accumulate through genetic drift rather than positive selection.
This accumulation is consistent over time, acting like a "molecular clock" that can be used to calculate evolutionary divergence timelines.
Types of Mutations
Base Pair Insertion: One or more nucleotide base pairs are inserted into the DNA sequence. The entire substance gets read differently
Base Pair Substitution: One nucleotide is replaced by another causing a stop codon and something random to be made
15.6 – Recombination, lateral gene transfer, gene duplication lead to new features.
Mechanisms that Preserve Variation in Populations:
Diploidy: Having two sets of chromosomes allows recessive alleles to "hide" and persist in heterozygotes.
Heterozygote Advantage: When heterozygotes have a higher fitness than either homozygote (e.g., Sickle Cell trait).
Balanced Polymorphism: The ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population.
Sexual Reproduction:
Advantage: Creates genetic variability through recombination (crossing over).
Disadvantage: The number of offspring tends to be much lower than with asexual reproduction.
Lateral Gene Transfer:
The transfer of genes, organelles, or genome fragments from one lineage to another, not from parent to offspring.
Example: A species may pick up DNA fragments directly from the environment.
Gene Duplication:
An entire gene is duplicated, allowing the new copy to mutate without harming the original function.
Outcomes:
Both copies retain the original function (increased efficiency).
One copy evolves a new function.
One copy may become functionless.
Examples:
Sickle Cell Anemia & Malaria: In Africa, heterozygotes (carriers) for the sickle cell allele are resistant to malaria but do not have severe anemia. This heterozygote advantage maintains the allele in the population.
Agriculture: Breeders use artificial selection (similar to natural selection) to enhance desired traits in crops and livestock, such as looking for beneficial genes in plants like rice.15.3 – Evolution can be measured by change in allele frequency
Key Concepts:
Natural Selection acts on Individuals (their traits, lifetime, gender, diet).
Evolution acts on Populations.
The 5 Agents of Evolutionary Change:
Mutation: A chemical change to DNA that could lead to evolution.
Gene Flow/Migration: The movement of organisms into or out of a population.
Non-Random Mating/Sexual Selection: When individuals (e.g., males with certain characteristics) are selected by others for mating.
Genetic Drift: A change in allele frequencies that happens mostly by chance in smaller populations.
Natural Selection: Differential survival based on traits.
Hardy-Weinberg Equilibrium (The "No Evolution" Null Hypothesis)
For a population to not evolve (be in equilibrium), the following conditions must be met:1. No genetic drift (very large population).
2. No gene flow (no migration in or out).
3. No mutations (no chemical change to DNA).
4. Random mating (no sexual selection).
5. No natural selection.
Hardy-Weinberg Equations:
Allele Frequency: p+q=1p+q=1
pp = frequency of dominant allele
qq = frequency of recessive allele
Genotype Frequency: p2+2pq+q2=1p2+2pq+q2=1
p2p2 = frequency of homozygous dominant genotype
2pq2pq = frequency of heterozygous genotype
q2q2 = frequency of homozygous recessive genotype
Example: PKU Allele Frequency
PKU is a recessive disorder, so affected individuals have genotype q2q2.
If 1 in 10,000 people have PKU, q2=0.0001q2=0.0001.
Therefore, q=0.0001=0.01q=0.0001=0.01.
Since p+q=1p+q=1, p=1−0.01=0.99p=1−0.01=0.99.
The frequency of carriers (heterozygotes, 2pq2pq) is 2∗0.99∗0.01=0.01982∗0.99∗0.01=0.0198, or about 2% of the population.
15.4 – Selection can be stabilizing, directional, or disruptive.
Trait Types:
Qualitative Traits: Influenced by alleles at a single locus; discrete categories (e.g., flower color).
Quantitative Traits: Influenced by alleles at multiple loci; show continuous variation (e.g., height, weight).
Models of Selection (that act on quantitative traits):
Stabilizing Selection:
Favors the average individuals.
Reduces variation in the population.
Directional Selection:
Favors individuals at one extreme of the trait distribution.
Shifts the average trait value in one direction.
Disruptive Selection:
Favors individuals at both extremes of the trait distribution.
Favors variation and can lead to two distinct phenotypes.
15.6 – Recombination, lateral gene transfer, gene duplication lead to new features.
Mechanisms that Preserve Variation in Populations:
Diploidy: Having two sets of chromosomes allows recessive alleles to "hide" and persist in heterozygotes.
Heterozygote Advantage: When heterozygotes have a higher fitness than either homozygote (e.g., Sickle Cell trait).
Balanced Polymorphism: The ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population.
Sexual Reproduction:
Advantage: Creates genetic variability through recombination (crossing over).
Disadvantage: The number of offspring tends to be much lower than with asexual reproduction.
Lateral Gene Transfer:
The transfer of genes, organelles, or genome fragments from one lineage to another, not from parent to offspring.
Example: A species may pick up DNA fragments directly from the environment.
Gene Duplication:
An entire gene is duplicated, allowing the new copy to mutate without harming the original function.
Outcomes:
Both copies retain the original function (increased efficiency).
One copy evolves a new function.
One copy may become functionless.
15.7 – Practical Applications of Evolution
Examples:
Sickle Cell Anemia & Malaria: In Africa, heterozygotes (carriers) for the sickle cell allele are resistant to malaria but do not have severe anemia. This heterozygote advantage maintains the allele in the population.
Agriculture: Breeders use artificial selection (similar to natural selection) to enhance desired traits in crops and livestock, such as looking for beneficial genes in plants like rice.Of course. Here are comprehensive notes based only on the content from the provided PDF.
***
### Comprehensive Notes from Biology2.pdf
#### 15.3 – Evolution can be measured by change in allele frequency
Key Concepts:
* Natural Selection acts on Individuals (their traits, lifetime, gender, diet).
* Evolution acts on Populations.
The 5 Agents of Evolutionary Change:
1. Mutation: A chemical change to DNA that could lead to evolution.
2. Gene Flow/Migration: The movement of organisms into or out of a population.
3. Non-Random Mating/Sexual Selection: When individuals (e.g., males with certain characteristics) are selected by others for mating.
4. Genetic Drift: A change in allele frequencies that happens mostly by chance in smaller populations.
5. Natural Selection: Differential survival based on traits.
Hardy-Weinberg Equilibrium (The "No Evolution" Null Hypothesis)
For a population to not evolve (be in equilibrium), the following conditions must be met:
* 1. No genetic drift (very large population).
* 2. No gene flow (no migration in or out).
* 3. No mutations (no chemical change to DNA).
* 4. Random mating (no sexual selection).
* 5. No natural selection.
Hardy-Weinberg Equations:
* Allele Frequency: \( p + q = 1 \)
* \( p \) = frequency of dominant allele
* \( q \) = frequency of recessive allele
* Genotype Frequency: \( p^2 + 2pq + q^2 = 1 \)
* \( p^2 \) = frequency of homozygous dominant genotype
* \( 2pq \) = frequency of heterozygous genotype
* \( q^2 \) = frequency of homozygous recessive genotype
Example: PKU Allele Frequency
* PKU is a recessive disorder, so affected individuals have genotype \( q^2 \).
* If 1 in 10,000 people have PKU, \( q^2 = 0.0001 \).
* Therefore, \( q = \sqrt{0.0001} = 0.01 \).
* Since \( p + q = 1 \), \( p = 1 - 0.01 = 0.99 \).
The frequency of carriers (heterozygotes, \( 2pq \)) is \( 2 0.99 0.01 = 0.0198 \), or about *2%** of the population.
---
#### 15.4 – Selection can be stabilizing, directional, or disruptive.
Trait Types:
* Qualitative Traits: Influenced by alleles at a single locus; discrete categories (e.g., flower color).
* Quantitative Traits: Influenced by alleles at multiple loci; show continuous variation (e.g., height, weight).
Models of Selection (that act on quantitative traits):
1. Stabilizing Selection:
Favors the *average** individuals.
* Reduces variation in the population.
2. Directional Selection:
Favors individuals at *one extreme** of the trait distribution.
* Shifts the average trait value in one direction.
3. Disruptive Selection:
Favors individuals at *both extremes** of the trait distribution.
* Favors variation and can lead to two distinct phenotypes.
---
#### 15.6 – Recombination, lateral gene transfer, gene duplication lead to new features.
Mechanisms that Preserve Variation in Populations:
* Diploidy: Having two sets of chromosomes allows recessive alleles to "hide" and persist in heterozygotes.
* Heterozygote Advantage: When heterozygotes have a higher fitness than either homozygote (e.g., Sickle Cell trait).
* Balanced Polymorphism: The ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population.
Sexual Reproduction:
* Advantage: Creates genetic variability through recombination (crossing over).
* Disadvantage: The number of offspring tends to be much lower than with asexual reproduction.
Lateral Gene Transfer:
The transfer of genes, organelles, or genome fragments from one lineage to another, not* from parent to offspring.
* Example: A species may pick up DNA fragments directly from the environment.
Gene Duplication:
* An entire gene is duplicated, allowing the new copy to mutate without harming the original function.
* Outcomes:
1. Both copies retain the original function (increased efficiency).
2. One copy evolves a new function.
3. One copy may become functionless.
---
#### 15.7 – Practical Applications of Evolution
Examples:
* Sickle Cell Anemia & Malaria: In Africa, heterozygotes (carriers) for the sickle cell allele are resistant to malaria but do not have severe anemia. This heterozygote advantage maintains the allele in the population.
* Agriculture: Breeders use artificial selection (similar to natural selection) to enhance desired traits in crops and livestock, such as looking for beneficial genes in plants like rice.Of course. Here are comprehensive notes based only on the content from the provided PDF.
***
### Comprehensive Notes from Biology2.pdf
#### 15.3 – Evolution can be measured by change in allele frequency
Key Concepts:
* Natural Selection acts on Individuals (their traits, lifetime, gender, diet).
* Evolution acts on Populations.
The 5 Agents of Evolutionary Change:
1. Mutation: A chemical change to DNA that could lead to evolution.
2. Gene Flow/Migration: The movement of organisms into or out of a population.
3. Non-Random Mating/Sexual Selection: When individuals (e.g., males with certain characteristics) are selected by others for mating.
4. Genetic Drift: A change in allele frequencies that happens mostly by chance in smaller populations.
5. Natural Selection: Differential survival based on traits.
Hardy-Weinberg Equilibrium (The "No Evolution" Null Hypothesis)
For a population to not evolve (be in equilibrium), the following conditions must be met:
* 1. No genetic drift (very large population).
* 2. No gene flow (no migration in or out).
* 3. No mutations (no chemical change to DNA).
* 4. Random mating (no sexual selection).
* 5. No natural selection.
Hardy-Weinberg Equations:
* Allele Frequency: \( p + q = 1 \)
* \( p \) = frequency of dominant allele
* \( q \) = frequency of recessive allele
* Genotype Frequency: \( p^2 + 2pq + q^2 = 1 \)
* \( p^2 \) = frequency of homozygous dominant genotype
* \( 2pq \) = frequency of heterozygous genotype
* \( q^2 \) = frequency of homozygous recessive genotype
Example: PKU Allele Frequency
* PKU is a recessive disorder, so affected individuals have genotype \( q^2 \).
* If 1 in 10,000 people have PKU, \( q^2 = 0.0001 \).
* Therefore, \( q = \sqrt{0.0001} = 0.01 \).
* Since \( p + q = 1 \), \( p = 1 - 0.01 = 0.99 \).
The frequency of carriers (heterozygotes, \( 2pq \)) is \( 2 0.99 0.01 = 0.0198 \), or about *2%** of the population.
---
#### 15.4 – Selection can be stabilizing, directional, or disruptive.
Trait Types:
* Qualitative Traits: Influenced by alleles at a single locus; discrete categories (e.g., flower color).
* Quantitative Traits: Influenced by alleles at multiple loci; show continuous variation (e.g., height, weight).
Models of Selection (that act on quantitative traits):
1. Stabilizing Selection:
Favors the *average** individuals.
* Reduces variation in the population.
2. Directional Selection:
Favors individuals at *one extreme** of the trait distribution.
* Shifts the average trait value in one direction.
3. Disruptive Selection:
Favors individuals at *both extremes** of the trait distribution.
* Favors variation and can lead to two distinct phenotypes.
---
#### 15.6 – Recombination, lateral gene transfer, gene duplication lead to new features.
Mechanisms that Preserve Variation in Populations:
* Diploidy: Having two sets of chromosomes allows recessive alleles to "hide" and persist in heterozygotes.
* Heterozygote Advantage: When heterozygotes have a higher fitness than either homozygote (e.g., Sickle Cell trait).
* Balanced Polymorphism: The ability of natural selection to maintain stable frequencies of two or more phenotypic forms in a population.
Sexual Reproduction:
* Advantage: Creates genetic variability through recombination (crossing over).
* Disadvantage: The number of offspring tends to be much lower than with asexual reproduction.
Lateral Gene Transfer:
The transfer of genes, organelles, or genome fragments from one lineage to another, not* from parent to offspring.
* Example: A species may pick up DNA fragments directly from the environment.
Gene Duplication:
* An entire gene is duplicated, allowing the new copy to mutate without harming the original function.
* Outcomes:
1. Both copies retain the original function (increased efficiency).
2. One copy evolves a new function.
3. One copy may become functionless.
---
#### 15.7 – Practical Applications of Evolution
Examples:
* Sickle Cell Anemia & Malaria: In Africa, heterozygotes (carriers) for the sickle cell allele are resistant to malaria but do not have severe anemia. This heterozygote advantage maintains the allele in the population.
* Agriculture: Breeders use artificial selection (similar to natural selection) to enhance desired traits in crops and livestock, such as looking for beneficial genes in plants like rice.