Population Genetics

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72 Terms

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Genotype

The letter representation of an allele/trait

  • Tt, TT, tt

  • What the genes say

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Phenotype

Physical expression of an allele

  • A flower being purple

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Allele

A version/variant of a gene

  • Long or short hair

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What are the three types of genotypes?

Homozygous dominant, homozygous recessive, heterozygous

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What does homozygous dominant mean?

Two of the same allele, and they are both dominant

  • TT

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What does homozygous recessive mean?

Two of the same allele, and they are both recessive

  • tt

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What does heterozygous mean?

Two different alleles, one dominant, and one recessive

  • Tt

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What are the two major Hardy-Weinberg Formulas?

p2 + 2 pq + q2 = 1      p + q = 1

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What does each piece of the Hardy-Weinberg Formulas mean?

p = frequency of the A allele

q = frequency of the a allele

p2 = frequency of AA in the population

q2 = frequency of aa in the population

2pq = frequency of Aa in the population

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What happens to the frequency of alleles over time?

The change (over generations)

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How many chromosomes do humans have?

46 = 23 sets

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What is the difference between diploid and haploid?

  • Examples?

Diploid = 2 copies of a gene (alleles)

Haploid = 1 copy of a gene

  • Diploid = somatic cells

  • Haploid = reproductive cells (gametes)

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How many alleles code for a gene?

Two or more

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Natural Selection acts on ________ but only __________ evolve

Natural Selection acts on individuals but only populations evolve

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Microevolution

A change in allele frequencies in a population over generations

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What are the causes of microevolution?

  • What are their opposites??

  1. Natural Selection = no selection

  2. Genetic Drift = large breeding population

  3. Gene Flow = no immigration or emigration

  4. Non-Random Mating = random mating

  5. Mutations = no mutations

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What causes genetic variation in individuals?

Differences in genes or other DNA segments

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What is a phenotype a product of?

Inherited genotype and environmental influences

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Can natural selection act on variation without a genetic component?

Nope

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Point mutation

A change in one base of a gene

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In what cases can a mutation be harmless/neutral?

When they are in the noncoding regions of the DNA or due to redundancy in the genetic code

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When can mutations be harmful

When they change protein production → in a negative way

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When can mutations be beneficial

When they change protein production → in a positive way

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What is the only way mutations can be passed on?

If they are in the sex cells

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What is gene duplication?

The duplication of a small piece of DNA(won’t generally do too much damage → compared to the duplication of a chromosome portion), this gene can take on new functions through further mutations

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What does sexual reproduction due in terms of alleles?

Shuffles existing alleles into new combinations

  • Recombination is more important than mutation for genetic differences

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What type of characters contribute to variation within a population?

Discrete (having a widow’s peak or not, either you have it or not) and quantitative characters (skin color = a gradient; controlled by many genes)

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How can genetic variation be measured?

Through gene or nucleotide variability

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What is gene variability

The average heterozygosity measures the average percent of loci that are heterozygous in a population

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What is nucleotide variability

The measurement by comparing the DNA sequences of pairs of individuals

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What is chromosomal variation among populations caused by?

Genetic drift, not natural selection

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Do species exhibit geographic variation?

Yes, many

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What is the Hardy-Weinberg equation used to test?

Whether a population is evolving

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Population

a localized group of individuals capable of interbreeding and producing fertile offspring

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What does a gene pool consist of?

All the alleles for all loci in a population

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When is a locus fixed?

If all individuals in a population are homozygous for the same allele

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What is a locus

A location

  • Where on a chromosome a specific gene is

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What is the total number of alleles at a locus for diploid organisms?

The total number of individuals divided by 2

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What is the total number of dominant alleles at a locus?

  • Recessive?

2 alleles for each homozygous dominant individual plus 1 allele for each heterozygous individual

  • Same principle for recessive

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What does the Hardy-Weinberg Principle describe?

A population that is not evolving

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What does the Hardy-Weinberg Principle state?

That frequencies of alleles and genotypes in a population remain constant from generation to generation

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In a given population where gametes contribute to the next generation randomly, will allele frequencies change?

No

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What does Mendelian Inheritance preserve?

Genetic variation in a population

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What is the condition for the hypothetical population in a Hardy-Weinberg theorem?

  • What a real populations like?

A population that is not evolving

  • Real populations have changing allele and genotype frequencies over time

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Can natural populations evolve at some loci and be at Hardy-Weinberg equilibrium at other loci?

Yes, they can

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What does genetic drift describe?

How allele frequencies fluctuate unpredictably from one generation to the next

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What are two methods by which genetic drift may occur?

Founder effect, and Bottleneck effect

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Founder Effect

  • Describe

Occurs when a few individuals become isolated from a larger population

  • Allele frequencies in the small founder population can be different from those in the larger parent population

  • For example, the minority of a population mat migrate, which does not represent the go population, but they will evolve and grow from that

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Bottleneck Effect

  • Describe

A sudden reduction in population size due to a change in the environment 

  • Usually associated with a natural disaster

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What are the main ideas of genetic drift?

  1. Genetic drift is significant in small populations

  2. Genetic drift causes allele frequencies to change at random

  3. Genetic drift can lead to a loss of genetic variation within populations

  4. Genetic drift can cause harmful alleles to become fixed

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What does gene flow consist of?

The movement of alleles among populations

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What does gene flow tend to do?

  • Why?

REDUCE variation among populations overtime?

  • If you have two species, A and B, and they reproduce together, both populations will almost merge, and get more and more similar to each other, reducing the variation between the two

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True or False: Gene flow decreases the fitness of a population only

No, it can both increase or decrease fitness

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What is the only mechanism that consistently causes adaptive evolution?

  • How?

Natural Selection

  • By acting on a organisms phenotype

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Are the terms “struggle for existence” and “survival of the fittest” accurate?

  • Why or why not?

No, because they imply direct competition

  • Reproductive success is generally more subtle and depends on many factors

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What is relative fitness

The contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

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What are the modes of selection?

  • Bell curves

  1. Directional selection

  2. Disruptive selection

  3. Stabilizing selection

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Directional selection

The curve shifts to the left or the right, toward one side of the spectrum

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Disruptive selection

The middle of the curve collapses, both extremes have higher frequencies

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Stabilizing selection

The middle is the only frequency, other extremes are virtually non-existent

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How does adaptive evolution occur?

  • Is it continuous, why?

It occurs as the match between an organism and its environment increases

  • Yes, it’s continuous because the environment can change

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What is sexual selection?

Natural selection for mating success

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What are the types of sexual selection?

  1. Intrasexual selection

  2. Intersexual selection

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What can sexual selection result in?

Sexual dimorphism

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What is intrasexual selection?

Fighting between the same sex for territory

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What is intersexual selection?

Females selecting a male to mate with(usually)

  • They usually mate with males who have won territory as they are better fit

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What is sexual dimorphism

The differences between males and females of a species

  • Appearance, behaviors(fighting)

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What is balancing selection?

  • What is included in it?

When multiple alleles are maintained in a population, which results in their preservation over long evolutionary time periods

  • Heterozygote advantage

  • Frequency-dependent selection

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What is an example of heterozygote advantage?

The sickle-cell alleles causing mutations in hemoglobin but also confers malaria resistance

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Frequency-Dependent Selection

Mimicking for example; a non dangerous animal with the pattern of a poisonous one) = from google

Frequency-dependent selection selects for approximately equal numbers of “right-mouthed” and “left-mouthed” scale-eating fish

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Why can’t natural selection create perfect organisms?

  1. Selection can act only on existing variations

  2. Evolution is limited by historical constraints

  3. Adaptations are often compromises

  4. Chance, natural selection, and the environment interact

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What is a cline?

A measurable gradient in a single characteristic (or biological trait) of a species across its geographical range.