evolution (bio 280) > Quiz 2 > Flashcards

Quiz 2 Flashcards

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1
Q

What is a population in evolutionary biology?

A

A group of individuals of the same species living in the same geographic area and capable of interbreeding.

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2
Q

Define gene pool

A

The total collection of all alleles at all loci in a population

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3
Q

What is allele frequency?

A

The proportion of a specific allele among all alleles at a locus in a population.

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4
Q

formula for calculating allele frequency

A

Allele frequency= Number of copies of allele​/total alleles (2N)

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5
Q

What is genotype frequency?

A

The proportion of individuals in a population with a specific genotype

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6
Q

formula to calculate genotype frequency

A

Genotype frequency=Number with genotype​/ total genes (N)

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7
Q

What is phenotype frequency?

A

The proportion of individuals expressing a particular phenotype.

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8
Q

hardy weinberg formula for allele frequencies

A

p+q=1

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9
Q

hardy weinberg formula for genotype frequencies

A

p^2+2pq+q^2=1

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10
Q

What is the modern synthesis of evolution?

A

The integration of Darwinian natural selection with Mendelian genetics

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11
Q

What disciplines did the modern synthesis connect?

A

Natural selection

Mendelian inheritance

Population genetics

Paleontology

Systematics

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12
Q

How is evolution defined in population genetics?

A

Evolution is a change in allele frequencies in a population across generations.

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13
Q

How do we determine if evolution is occurring?

A

If allele frequencies change from one generation to the next, evolution is occurring.

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14
Q

What does Hardy-Weinberg equilibrium predict?

A

If certain conditions are met, allele and genotype frequencies remain constant from generation to generation.

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15
Q

What are the five assumptions of Hardy-Weinberg equilibrium?

A

No mutation

No migration (gene flow)

Large population size (no genetic drift)

Random mating

No natural selection

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16
Q

Why is Hardy-Weinberg used as a null model?

A

It represents a baseline expectation of no evolutionary change. Deviations suggest evolutionary forces are acting.

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17
Q

How do Hardy-Weinberg assumptions link to evolutionary mechanisms?

A

Mutation → new alleles

Migration → gene flow

Small population → genetic drift

Nonrandom mating → changes genotype frequencies

Selection → differential survival/reproduction

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18
Q

How are Hardy-Weinberg genotype frequencies derived?

A

(p+q)(p+q)=p^2+2pq+q^2

its literally just a punett square

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19
Q

How do you derive HWE predictions for three alleles (A₁, A₂, A₃)?

A

(p+q+r)^2 expands to
p^2+q^2+r^2+2pq+2qr+2pr

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20
Q

If a population is in HWE and recessive phenotype frequency (aa) = 0.16, how do you find allele frequencies?

A

q^2=0.16
q=0.4
p=1−q=0.6

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21
Q

Once you know p and q, how do you find genotype frequencies?

A

AA=p^2
Aa=2pq
aa=q^2

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22
Q

What is the alternative hypothesis (H₁) when testing for HWE?

A

The population is not in Hardy-Weinberg equilibrium.

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23
Q

Steps to perform chi-square test for HWE?

A

1) Calculate allele frequencies
2) Calculate expected genotype frequencies (p², 2pq, q²)
3) Convert frequencies to expected counts
4) Calculate χ²
5) Determine degrees of freedom
6) Compare to χ² critical value
7) Accept or reject H₀

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24
Q

Degrees of freedom for HWE?

A

df = number of genotypes − number of alleles

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25
Degrees of freedom for two alleles?
3 genotypes − 2 alleles = 1 df
26
When do you reject the null hypothesis?
If calculated χ² > critical value from table → reject H₀ → population not in HWE.
27
Does nonrandom mating change allele frequencies?
No — it changes genotype frequencies but not allele frequencies.
28
Which forces directly change allele frequencies?
Natural selection Genetic drift Gene flow Mutation
29
Why is large population size important in HWE?
Prevents genetic drift (random allele frequency changes).
30
What does it mean biologically if a population deviates from HWE?
At least one evolutionary force is acting.
31
Why is HWE powerful in evolutionary biology?
It allows us to detect evolution quantitatively by comparing observed vs. expected genotype frequencies.
32
How do mutations create variation in a population?
Mutations alter DNA sequence, producing new alleles. These new alleles introduce heritable genetic variation—the raw material for evolution.
33
What is a mutation?
A permanent change in the nucleotide sequence of DNA.
34
What is a small-scale (point) mutation?
a genetic alteration involving the substitution, insertion, or deletion of a single nucleotide base in DNA, affecting one or a few nucleotides.
35
Silent mutation
A nucleotide change that does not alter the amino acid due to redundancy in the genetic code.
36
Missense mutation
diff amino acid
37
Nonsense mutation
premature stop codon
38
Frameshift mutation
Insertion or deletion not in multiples of three nucleotides, altering reading frame
39
How can changes in amino acid sequence influence protein function?
Affect folding, active site shape, stability, or interactions.
40
What are examples of large-scale mutations?
Gene duplication Chromosomal inversion Translocation Large deletion Aneuploidy
41
What is aneuploidy?
An abnormal number of chromosomes caused by nondisjunction during meiosis.
42
How do we measure whether a mutation is beneficial, deleterious, or neutral?
By assessing its effect on relative fitness (survival and reproductive success).
43
Why are most mutations neutral?
Much DNA is noncoding Many Amino Acid Changes Do Not Disrupt Protein Function Some amino acid substitutions are similar Redundancy of genetic code
44
Germline vs. somatic mutations
Germline: occur in gamete-producing cells → heritable Somatic: occur in body cells → not inherited
45
Why is mutation rate important for evolution?
It determines how quickly new variation enters populations.
46
Factors affecting mutation rate:
DNA replication error rate DNA repair efficiency Genome Structure and Size Generation time
47
What role does mutation play in population variation?
Mutation generates new alleles; other forces (selection, drift, gene flow) change their frequencies.
48
How does sexual reproduction increase genetic variation?
Independent assortment Crossing over Random fertilization
49
What is crossing over? When does it occur?
Exchange of DNA between homologous chromosomes during Prophase I of meiosis.
50
How does crossing over increase variation?
It creates recombinant chromosomes with new combinations of alleles.
51
What is independent assortment?
Random orientation of homologous chromosome pairs during Metaphase I. Each pair segregates independently.
52
At what stage does independent assortment occur?
Metaphase I of meiosis.
53
How many distinct gametes can an organism produce via independent assortment?
2^n Where n = haploid chromosome number.
54
What is a gamete?
A haploid reproductive cell (sperm or egg).
55
What is random fertilization?
Any sperm can fuse with any egg, multiplying genetic combinations and increasing variation.
56
How do segregation and random fertilization predict inheritance?
Segregation determines gamete allele frequencies. Random fertilization determines how those gametes combine. Together, they allow calculation of expected genotype and phenotype ratios.
57
Dominant vs. recessive allele expression
Dominant: expressed in heterozygotes and homozygotes Recessive: expressed only in homozygotes Dominance does not imply evolutionary advantage.
58
What is genetic polymorphism?
Presence of two or more alleles at appreciable frequency within a population.
59
Why do most traits not show simple dominant–recessive inheritance?
Because many traits are: Polygenic Quantitative Influenced by environment epistasis and pleiotropy
60
What is a quantitative trait?
influenced by multiple genes (polygenic) and environmental factors, showing continuous variation within a population rather than distinct, "either-or" categories.
61
What is polyphenism?
Environmentally induced production of discrete phenotypes from a single genotype.
62
Polyphenism vs. genetic polymorphism
Polyphenism: one genotype → multiple phenotypes (environmental trigger) Genetic polymorphism: multiple genotypes → multiple phenotypes
63
What is phenotypic plasticity?
The ability of a genotype to produce different phenotypes across environments. Plasticity ≠ evolution unless allele frequencies change.
64
What is a reaction norm?
A graph showing phenotype expression across environments for a genotype. Greater slope = greater plasticity.
65
Sequence of meiosis stages relevant to variation
Prophase I → crossing over Metaphase I → independent assortment Anaphase I → homologs separate Meiosis II → sister chromatids separate
66
How do ploidy levels affect gamete diversity?
Greater chromosome number (n) → exponentially more possible gametes via 2ⁿ combinations.
67
Deleterious mutation
Reduces relative fitness.
68
Fertilization
Fusion of two haploid gametes to form a diploid zygote.
69
What is natural selection?
A process in which individuals with heritable traits that increase fitness leave more offspring, causing allele frequencies to change across generations. Evolution by natural selection = change in allele frequencies due to differential reproductive success.
70
State Darwin’s four postulates (requirements) for natural selection.
Variation exists among individuals in a population. Some variation is heritable. More offspring are produced than can survive (struggle for existence). Individuals with certain traits have higher fitness (differential survival and reproduction). If all four occur, evolution by natural selection will happen.
71
Define fitness.
Fitness is an individual’s reproductive success relative to others in the population, measured by survival and number of offspring contributed to the next generation. Fitness is a property of individuals, not populations.
72
How do differences in fitness drive natural selection?
If individuals with genotype A leave more offspring than those with genotype a, allele A increases in frequency over generations. Selection acts on phenotypes but changes allele frequencies.
73
Apply Darwin’s postulates to a scenario. Example Setup: In a drought, plants vary in root depth.
Variation: Some plants have deep roots, others shallow. Heritability: Root depth is genetically influenced. Overproduction: Not all seedlings survive drought. Differential fitness: Deep-rooted plants survive and reproduce more. Prediction: Alleles for deeper roots increase.
74
Absolute fitness (W)
The average number of offspring produced by individuals of a genotype.
75
Relative fitness (w)
Absolute fitness of a genotype divided by the highest absolute fitness in the population. w=W/Wmax
76
Selection coefficient (s)
The reduction in fitness relative to the most fit genotype. s=1−w
77
Average excess of fitness
The difference between the fitness of individuals carrying a particular allele and the population’s average fitness.
78
Why is fitness measured at the individual level?
Because selection acts on differences among individuals. Populations evolve, but individuals compete and reproduce.
79
How do you calculate average fitness of the population? W
Multiply genotype frequencies by their relative fitness values and sum them. This predicts overall evolutionary change.
80
How does average excess of fitness predict allele change?
If allele A has positive average excess → frequency increases. If negative → frequency decreases. This directly links genotype fitness to allele frequency change.
81
How do Darwin’s postulates connect to relative fitness calculations?
Postulate 4 (differential fitness) is quantified using relative fitness. Fitness differences allow prediction of allele frequency change
82
What happens to average fitness under directional selection?
It typically increases over time as advantageous alleles rise in frequency.
83
The average excess of fitness gives
A measurement of how much an allele contributes to fitness
84
how are relative fitness and selection coefficient correlated
higher fitness=lower selection coefficient
85
what does a low selection coefficient mean
no selection against the phenotype
86
define inbreeding
positive non-random mating between related individuals
87
How can antagonistic pleiotropy complicate predictions of selection?
A beneficial effect on one trait may have a deleterious effect on another, constraining evolutionary outcomes.
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