Lecture 19 Flashcards
Does evolution occur in individuals or populations?
Evolution occurs in populations over successive generations, not within individual lifetimes (NOT individuals)
What are populations in the context of evolution?
Populations consist of all individuals of the same species living in a specific area at the same time, exhibiting variations in traits, some of which are inherited.
How does evolutionary change occur?
from one generation to the next, primarily through genetic variations
Why is genetics considered the basis of evolution?
Genetics determines how traits are passed from one generation to the next
What did Darwin not understand regarding the transmission of traits?
Darwin lacked an understanding of how traits were inherited from one generation to the next.
Between Darwin and Mendel, What did each talk about? (to explain evolution)
Darwin = NAtrual selection to explain evolution
Mendel = Principles of inheritance
What did both of these Theories come about?
Population Genetics
What is Population Genetics?
Science that studies the process of microevolution (Science that studies the process of microevolution)
What is Microevolution?
Is a change in the genetic makeup of a
population from generation to generation
Evolutionary change below what level?
below the species level
Can microevolution eventually lead to macroevolution?
YES
Why is this considered microevolution?
because although it doesn’t result in the formation of a new species, the genetic makeup of the population changes significantly
(no new species BUT genetics differ)
Describe the scenario of the abandoned mine.
The soil is rich in toxic heavy metals, allowing only grass seeds with alleles for heavy-metal tolerance to germinate, grow, and reproduce.
What happens to the offspring of plants with heavy-metal tolerance?
These plants tend to produce offspring with metal-tolerant traits.
What is the consequence of this selective pressure on the population? (over time)
the frequency of the allele for heavy-metal tolerance increases in the population
How has the genetic makeup of the population changed?
non-resistant alleles were dominant, but over time, heavy-metal-resistant alleles became dominant in that area.
What is Macroevolution? (in simple terms)
new species, new groups
What defines the gene pool of a population?
alleles for all the loci present in the population
How many alleles do diploid organisms typically have at each genetic locus?
two alleles at each genetic locus
Why do individuals within a population exhibit variations in traits?
due to genes coming in different allelic forms
How do individuals contribute to the gene pool of a population?
Each individual contributes only a small fraction of the alleles present in the population’s gene pool.
Provide an example of genetic variation in humans.
Humans exhibit genetic variation in traits such as hair color, eye color, etc., which result from different allelic forms of genes.
What is Genotype frequency?
The proportion of a particular genotype in the population
What is Allele frequency?
proportion of a specific allele in a population
What defines genetic equilibrium in a population? (when does it occur?)
occurs when the frequencies of alleles and genotypes do not change from one generation to the next.
How does the Hardy-Weinberg principle relate to genetic equilibrium?
The Hardy-Weinberg principle states that allele and genotype frequencies remain constant over generations in the absence of evolutionary influences, indicating genetic equilibrium.
What is the significance of genetic equilibrium?
population is not evolving for the gene locus being studied
Describe a population that is not at genetic equilibrium.
A population experiencing changes in allele frequencies over generations is not at genetic equilibrium and is undergoing evolution.
How does genetic equilibrium relate to the Hardy-Weinberg principle?
The Hardy-Weinberg principle serves as a mathematical model to determine whether a population is at genetic equilibrium or if evolution is occurring.
What conditions characterize a population in Hardy-Weinberg equilibrium?
all male-female matings occur randomly, leading to stable allele frequencies over generations.
How does the Hardy-Weinberg principle help understand population genetics?
The Hardy-Weinberg principle provides a BASELINE expectation for genotype and allele frequencies in a population that is not undergoing evolutionary changes, offering insight into population genetics.
Why do populations rarely stay in Hardy-Weinberg equilibrium in nature?
Due to various evolutionary pressures like natural selection, genetic drift, and gene flow, which alter allele frequencies.
What’s the significance of identifying populations in Hardy-Weinberg equilibrium?
It helps understand evolutionary processes and factors influencing genetic variation.
How can you calculate the value of one allele frequency if you know the other?
(what is the equation?)
p + q = 1
In this equation: p + q = 1
What is p and what is q?
p = one allele frequency
q = represents the other
If p equals 0.7, what is the value of q?
q = 0.3
Explain the significance of squaring both sides of the equation p + q = 1.
It helps describe the relationship between genotype frequencies, comparing the frequencies of homozygous dominant (p²), heterozygous (2pq), and homozygous recessive (q²) genotypes.
How is the equation p² + 2pq + q² = 1 used in population genetics?
It represents the distribution of genotype frequencies in a population, ensuring that the sum of all genotype frequencies equals 1.
What does each term in the equation
p² + 2pq + q² represent?
p² = the frequency of homozygous dominant genotypes (AA)
2pq = the frequency of heterozygous genotypes (Aa)
q² = the frequency of homozygous recessive genotypes (aa).
How can you simplify this answer?
p² = homozygous DOMINANT (AA)
2pq = heterozygous genotypes (Aa)
q² = homozygous RECESSIVE (aa).
Which equation is used fro genotype frquencies?
p² + 2pq + q² = 1
Which equation is used for allele frequencies?
p + q =1
What is the particularity about the allele frequencies?
For locus with only 2 ALLELES
When is a population considered to be at genetic equilibrium?
when the distribution of alleles conforms to the equation p² + 2pq + q² = 1.
What does the Hardy-Weinberg principle of genetic equilibrium tell us?
It predicts the expectations when a sexually reproducing population is not evolving.
What are the conditions required for genetic equilibrium to occur? (5)
Random mating
No mutation
No natural selection
Extremely large population size
No migration (no gene flow)
Do real populations often meet the conditions for genetic equilibrium?
NO
What does the degree of departure between observed and expected allele frequencies by the Hardy-Weinberg principle indicate?
It indicates the amount of evolutionary change.
Name 5 factors causing microevolution:
- mutations
- sexual recombination
- natural selection
- Genetic Drift
- Gene flow
What is evolution?
Changes in allele or genotype frequencies within a population over generations.
What do we call a change in the nucleotide sequence of an organism’s DNA?
Mutation!
How do new genes and alleles originate?
New genes and alleles originate only by mutation.
Where do most mutations occur?
most in somatic cells (not gametes)
Can mutations in somatic cells be passed on to offspring?
NO
Which mutations can be passed on to offspring?
only mutations in GAMETES
What is the typical mutation rate in animals and plants? (one in every ______ genes)
The mutation rate tends to be low in animals and plants, averaging about one in every 100,000 genes per generation.
In which organisms are mutations more rapid?
in microorganisms
Name an important microorganism
Bacteria
What is sexual recombination?
process by which genetic material from two parents is combined to produce offspring
With unique or identical combinations of alleles?
With UNIQUE combinations
Sexual recombination contributes to WHAT?
genetic variation
Is sexual recombination more important than mutation in producing genetic differences?
YES
What is the significance of genetic variation in evolution?
the raw material for natural selection to act upon
What does genetic variation lead to?
to adaptation and evolutionary change
Does the presence of genetic variation guarantee evolution?
no, not necessarily
Evolution also depends on what other factors? (3)
natural selection, genetic drift and gene flow
What is differential success in reproduction?
the phenomenon where certain alleles are passed to the next generation in greater proportions due to the reproductive success of individuals carrying those alleles.
How does differential success in reproduction affect allele frequencies?
Alleles linked to advantageous traits increase in frequency, while those tied to less favorable traits decrease.
Can you give an example of natural selection?
Sure, like predators favoring prey with certain traits, causing those traits to become more common in the population over time.
What are random evolutionary changes in a population?
They describe unpredictable fluctuations in allele frequencies from one generation to the next.
How do random evolutionary changes affect genetic variation?
They can DECREASE genetic variation within a population
They can INCREASE genetic differences among different populations.
What influences the likelihood of random evolutionary changes?
The size of the population sample, with smaller samples having a greater chance of deviation from predicted results.
What are the two situations that may result in genetic drift in small population sizes?
a) Bottleneck effect
b) Founder effect
What is the bottleneck effect?
Reduction in population size due to a disaster or other event.
How does the bottleneck effect occur?
When a large population is drastically reduced, leading to random fluctuations in allele frequencies.
What happens to alleles during the bottleneck effect? (3)
overrepresented, underrepresented or lost entirely.
How does genetic drift continue to change the gene pool after a bottleneck event?
Genetic drift persists until the population size is large enough to counteract chance fluctuations.
When does the bottleneck effect cease to influence the population’s genetic makeup?
When the population size becomes large enough to stabilize allele frequencies through genetic drift.
What is the founder effect?
When a small group establishes a new population with limited genetic variation.
How does the founder effect occur?
When a small number of individuals migrate or become isolated, establish a new colony.
What happens to genetic variability during the founder effect?
The new population exhibits allele frequencies different from the original population due to the limited genetic diversity brought by the founding individuals.
Can you provide an example of the founder effect?
The descent of 8000 individuals from only three couples of Old Order Amish, resulted in a high frequency of a rare recessive trait like dwarfism.
What is gene flow?
The movement of fertile individuals between populations, results in the transfer of alleles.
How does gene flow affect genetic variability?
It can lead to the loss of alleles in one population and the gain of alleles in another, thereby altering genetic variability.
What is the impact of gene flow on population differences?
It tends to reduce differences b/w populations
How does it reduce differences? (by what?)
by mixing individuals and their alleles
What does gene flow counteract other evolutionary forces? (2)
It can counteract genetic drift and natural selection
How does gene flow counteract other evolutionary forces?
by introducing new alleles and reducing genetic differentiation between populations.
What is one outcome of gene flow? (+ due to what?)
The increased genetic variability within populations is due to the influx of new alleles.
What is natural selection?
It’s the process where organisms with certain traits survive and reproduce better than others.
How does natural selection lead to adaptation?
By favoring advantageous traits in a population over time.
What are the factors causing microevolution? (5)
Mutations, sexual recombination, natural selection, genetic drift, and gene flow.
How does natural selection differ from other mechanisms of evolution?
It’s non-random and adaptive, selecting traits beneficial for survival and reproduction.
What is the ultimate outcome of natural selection?
GRADUAL adaptation of a population to its environment.
Natural Selection can alter frequencies, what are the 3 different subcategories of Natural selection?
- Directional selection
- Disruptive selection
- Stabilizing selection
Which one Favors intermediate variants (acts against extreme phenotypes)
- Stabilizing selection
Which one favors individuals at one end of the
phenotypic range
- Directional selection
What is Disruptive selection then? (what does it favor?)
Favors individuals at BOTH extremes of the
phenotypic range
How does sexual reproduction contribute to genetic variation?
unique combination of alleles inherited from two parents.
What are the 3 mechanisms involved in generating genetic diversity through sexual reproduction?
- crossing over
- independent assortment
- random fertilization
Why does sexual reproduction typically result in fewer offspring compared to asexual reproduction?
B/c it requires the union of two gametes, which can limit the number of offspring produced.
If sexual reproduction is a handicap, why has it persisted?
it produces genetic variation that may aid in
disease resistance
Is this long or short-term?
SHORT-term
What is sexual selection?
natural selection for mating success
What can sexual selection result in?
sexual dimorphism
What is sexual dimorphism?
marked differences between the sexes in secondary sexual characteristics
What are the 2 types of sexual selection?
- INTRAsexual selection
- INTERsexual selection
What is intrasexual selection?
Direct competition among individuals of one sex for mates of the opposite sex.
Can you explain intersexual selection?
It occurs when individuals of one sex, often females, are selective in choosing their mates from individuals of the other sex.
