Polygenic Traits and Natural Selection
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Questions and Answers

What is the effect of having more genes involved in a trait's expression?

It increases the range of phenotypes produced.

How does the ratio of polygenic traits compare to Mendelian ratios?

The ratio departs from the typical 9:3:3:1 Mendelian ratio.

What type of distribution do polygenic traits typically exhibit?

A normal (Gaussian) distribution.

Provide an example of a polygenic trait influenced by the environment.

<p>Human height influenced by diet.</p> Signup and view all the answers

What is a characteristic of a polygenic character in terms of phenotype?

<p>Several different genotypes may produce the same phenotype.</p> Signup and view all the answers

What role does continuous variation play in polygenic traits?

<p>It results in a blending of traits where one phenotype merges into another.</p> Signup and view all the answers

Why might skin color vary among individuals?

<p>It is influenced by genetic factors and environmental factors like UV light.</p> Signup and view all the answers

What evolutionary mechanism drives polygenic traits?

<p>Natural selection acts on the variability of polygenic traits.</p> Signup and view all the answers

What was the primary driving force behind the phenotypic change in the peppered moth population during the industrial revolution?

<p>Natural selection due to predation was the primary driving force.</p> Signup and view all the answers

In what year did dark-colored moths constitute 98% of the peppered moth population?

<p>In 1895, dark-colored moths made up 98% of the population.</p> Signup and view all the answers

What were the results of Kettlewell's comparison of survival rates for dark and light moths in polluted versus unpolluted environments?

<p>Dark moths survived better in polluted environments, while light moths had a higher survival rate in unpolluted forests.</p> Signup and view all the answers

What percentage of the peppered moth population was dark-colored in 1848?

<p>In 1848, 5% of the population were dark-colored moths.</p> Signup and view all the answers

Describe the role of genetic factors in the evolution of the peppered moth’s coloration.

<p>There is a genetic component to the coloration trait, which allows it to be transmitted across generations.</p> Signup and view all the answers

How did changes in tree coloration due to pollution affect peppered moth populations?

<p>The pollution caused trees to become darker, favoring the survival of dark-colored moths over lighter ones.</p> Signup and view all the answers

What phenomenon is illustrated by the changes in the peppered moth population due to industrial pollution?

<p>The phenomenon is known as industrial melanism.</p> Signup and view all the answers

How does natural selection influence allele frequencies for single-gene traits?

<p>Natural selection can increase the frequency of advantageous alleles, causing changes in phenotype frequencies over time.</p> Signup and view all the answers

In what way does natural selection affect polygenic traits differently than single-gene traits?

<p>Natural selection on polygenic traits influences the distribution of phenotypes, often resulting in a bell curve formation with varying fitness levels.</p> Signup and view all the answers

What are the three types of selection that can impact polygenic traits?

<p>Directional selection, stabilizing selection, and disruptive selection.</p> Signup and view all the answers

What is the relationship between variance and standard deviation in a dataset?

<p>Variance measures the variability within a group of measurements, while standard deviation is the square root of the variance.</p> Signup and view all the answers

How does correlation relate to the study of traits in natural selection?

<p>Correlation indicates that a change in one trait is associated with a change in another, but it does not imply causation.</p> Signup and view all the answers

Explain why the allele for black color in lizards might increase due to natural selection.

<p>Black lizards absorb more sunlight, allowing them to have higher body temperatures, which enhances their speed and predator evasion.</p> Signup and view all the answers

What does it mean when it is said that traits are not independent in a biological context?

<p>It means that the distribution of one trait can influence or be influenced by the presence of other traits.</p> Signup and view all the answers

What would be the effect of stabilizing selection on a polygenic trait?

<p>Stabilizing selection would favor intermediate phenotypes, reducing the variance and resulting in a narrower bell curve.</p> Signup and view all the answers

What does the variable 's' represent in the context of the Univariate breeder's equation?

<p>'s' represents the difference between the mean after selection and the mean before selection.</p> Signup and view all the answers

How can narrow-sense heritability (h2) be estimated using the variables in the breeder's equation?

<p>Narrow-sense heritability can be estimated using the formula h2 = r/s.</p> Signup and view all the answers

Explain the significance of the 'MeanNext Generation' value in evolutionary biology.

<p>MeanNext Generation indicates the average trait value of the offspring after selection.</p> Signup and view all the answers

Why is it important to consider both the intensity of selection and heritability in prediction models?

<p>Both factors influence the evolutionary response of traits—a higher selection intensity or heritability typically results in greater change.</p> Signup and view all the answers

What does the response to directional selection (r) describe in the context of phenotypic traits?

<p>Response to directional selection describes the change in mean trait value from one generation to the next.</p> Signup and view all the answers

What impact does selection on one phenotypic trait have on other correlated traits?

<p>Selection on one trait can indirectly affect other traits due to their genetic correlations.</p> Signup and view all the answers

What factors contribute to the variance in phenotype (VP) according to the equation provided?

<p>VP includes variance from VA, VD, VI, and the interaction term VG X E.</p> Signup and view all the answers

Define 'reaction norm' in the context of genotypes and environments.

<p>'Reaction norm' refers to the set of phenotypes that a given genotype can produce across various environments.</p> Signup and view all the answers

Define realized heritability in the context of the breeder's equation.

<p>Realized heritability refers to the observed heritability calculated from the response of the population to selection.</p> Signup and view all the answers

Explain the significance of heritability (H2) in understanding phenotypic variation.

<p>Heritability quantifies the proportion of phenotypic variance that can be attributed to genetic differences.</p> Signup and view all the answers

What is the relationship between MeanAfter, MeanBefore, and the subsequent generation in the selection process?

<p>MeanAfter is used to determine 's', which influences the mean trait value in the next generation.</p> Signup and view all the answers

What does it imply if H2 equals 0 or 1?

<p>H2 = 0 implies no genetic contribution to phenotypic variance, while H2 = 1 indicates complete genetic determination of the variance.</p> Signup and view all the answers

How can narrow sense heritability (h2) be estimated?

<p>Narrow sense heritability can be estimated by analyzing the resemblance between related individuals or measuring population response to selection.</p> Signup and view all the answers

What is the role of twins in estimating heritability?

<p>Twins can be used to analyze genetic variation by comparing traits between identical and fraternal twins.</p> Signup and view all the answers

What does phenotypic variation suggest in relation to the nature-nurture debate?

<p>Phenotypic variation raises the question of whether differences in traits are due to genetic or environmental factors.</p> Signup and view all the answers

Describe the implications of finding that relatives have more similar trait values than unrelated individuals.

<p>This finding suggests a genetic basis for the trait under study, supporting the influence of heritability.</p> Signup and view all the answers

What does the equation $Vp = Vg + Ve + Vge$ signify in the context of phenotypic variation?

<p>It signifies that phenotypic variance ($Vp$) is composed of genetic variance ($Vg$), environmental variance ($Ve$), and the interaction between genetic and environmental variance ($Vge$).</p> Signup and view all the answers

Describe the significance of additive genetic variance ($Va$) in phenotypic variation.

<p>Additive genetic variance ($Va$) is crucial because it represents the portion of genetic variance that can be passed on to offspring, influencing traits in subsequent generations.</p> Signup and view all the answers

How does dominance genetic variance ($Vd$) differ from additive genetic variance ($Va$)?

<p>Dominance genetic variance ($Vd$) arises from the interaction between alleles at a single locus, while additive genetic variance ($Va$) is the cumulative effect of individual alleles across multiple loci.</p> Signup and view all the answers

What role does environmental variance ($Ve$) play in the phenotypic variation of a trait?

<p>Environmental variance ($Ve$) accounts for differences in traits due to environmental factors rather than genetic differences among individuals.</p> Signup and view all the answers

Explain the concept of pleiotropy and its influence on genetic variance.

<p>Pleiotropy occurs when a single gene affects multiple phenotypic traits, thus contributing to genetic variance by linking traits that may otherwise appear unrelated.</p> Signup and view all the answers

What does the term 'epistasis' refer to in the context of genetic variance?

<p>Epistasis refers to the interaction between genes at different loci, where the effect of one gene is modified by one or more other genes.</p> Signup and view all the answers

Why is it important to consider maternal genetic variance ($Maternal , VG$) and maternal environmental variance ($Maternal , VE$) when studying phenotypic variation?

<p>These factors are important as they reflect the genetic and environmental influences from the mother that can impact the offspring's traits, adding another layer of complexity to their development.</p> Signup and view all the answers

Define genetic-environmental interaction variance ($Vge$) and its relevance in understanding phenotypic variation.

<p>Genetic-environmental interaction variance ($Vge$) represents the differential effects of genotypes across varying environmental conditions, highlighting how environmental factors can influence genetic expression.</p> Signup and view all the answers

What is the significance of epigenetic factors in the context of genetic variance?

<p>Epigenetic factors are significant because they can alter gene expression without changing the underlying DNA sequence, thereby influencing phenotypic traits and potentially affecting inheritance patterns.</p> Signup and view all the answers

Discuss the implications of genetic variance not being entirely heritable.

<p>The implication is that only the additive genetic variance can be reliably passed on to future generations, limiting the capacity for certain traits to evolve through genetic inheritance alone.</p> Signup and view all the answers

Flashcards

Peppered Moth

A moth species with two color variations: light and dark, which both have a survival advantage depending on the environment.

Industrial Melanism

The phenomenon where dark-colored organisms become prevalent in polluted environments due to natural selection.

Natural Selection

The process where organisms with traits better suited to their environment survive and reproduce more successfully.

Coloration Pattern

The specific colors and patterns on an organism's body, which can play a role in camouflage, signaling, and mate selection.

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Environmental Pressure

A factor in the environment that influences the survival and reproduction of organisms.

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Survival Advantage

A trait that helps an organism survive and reproduce more successfully in a particular environment.

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Genetic Component

The inheritance of traits through genes, which can be influenced by natural selection.

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Evolutionary Change

The process of gradual changes in the traits of a population over multiple generations.

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Polygenic Inheritance

A trait controlled by the interaction of multiple genes, each having a small additive effect. This results in continuous variation in phenotypes.

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Phenotype Distribution

In polygenic traits, the distribution of phenotypes forms a bell-shaped curve, with most individuals exhibiting intermediate traits and fewer having extreme phenotypes.

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Epistasis

The interaction of genes where the expression of one gene alters the expression of another, leading to unexpected phenotypes.

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Environmental Influence

Polygenic traits can be influenced by environmental factors, leading to variation in phenotypes even among individuals with the same genotype.

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Continuous Variation

A characteristic of polygenic traits where phenotypes smoothly blend into each other, with no distinct categories.

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Genotype-Phenotype Relationship

In polygenic traits, multiple genotypes can result in the same phenotype, making it harder to predict an individual's genotype based on their phenotype alone.

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Human Height

A classic example of a polygenic trait influenced by both genetics and environmental factors, such as diet and nutrition.

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Evolution of Polygenic Traits

The evolution of polygenic traits is driven by multiple factors, including natural selection, genetic drift, and gene flow. These factors influence the frequencies of alleles contributing to the traits.

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Allele Frequency Change

The proportion of a specific allele in a population changes over generations, influenced by natural selection.

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Natural Selection on Single-Gene Traits

Natural selection acting on traits controlled by a single gene can lead to changes in the frequency of that gene's alleles in a population, resulting in changes in the frequency of different phenotypes.

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Polygenic Traits and Natural Selection

When traits are influenced by many genes, the distribution of phenotypes often forms a bell curve. Natural selection can affect this distribution by favoring individuals at one end of the curve, leading to changes in the average phenotype.

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Directional Selection

Shifting the distribution of phenotypes towards one extreme, favoring individuals with a particular trait.

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Stabilizing Selection

Maintaining the status quo, favoring individuals with the average phenotype and reducing the extremes.

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Disruptive Selection

Favoring individuals with extreme phenotypes at both ends of the distribution, often leading to two distinct populations.

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Correlation

When two characteristics are linked, a change in one is usually associated with a change in the other.

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Correlation Coefficient

A measure of the strength of the association between two characteristics.

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Phenotypic Variation

The differences in observable traits among individuals in a population. These traits can include physical characteristics, behavior, and other measurable aspects of an organism.

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Heritability

A measure of how much variation in a trait is due to genetic differences among individuals. It tells us the proportion of phenotypic variation that can be attributed to inherited factors.

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Broad Sense Heritability (H2)

The proportion of total phenotypic variation that is due to genetic differences. It includes all genetic effects, such as additive, dominance, and epistatic interactions.

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Narrow Sense Heritability (h2)

The proportion of phenotypic variation that is due to additive genetic effects, which are passed down from parents to offspring in a predictable way.

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Genetic Variance (Vg)

The variation in a trait that is caused by genetic differences among individuals.

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Environmental Variance (Ve)

The variation in a trait that is caused by environmental factors, such as diet, temperature, or exposure to toxins.

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Reaction Norm

The set of phenotypes produced by a given genotype across a range of environments. It shows how a genotype responds differently to different environmental conditions.

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Phenotypic Plasticity

The ability of an organism to change its phenotype in response to environmental cues. It reflects the flexibility in how genotypes express themselves in different environments.

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Selection Differential (s)

The difference in the mean trait value between the selected individuals and the original population before selection. It quantifies the intensity of selection for a particular trait.

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Response to Selection (r)

The change in the mean trait value of the offspring generation compared to the original population. It measures the effect of selection on the population's trait over time.

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Breeder's Equation (r = h2 s)

A fundamental equation in quantitative genetics that predicts the response to selection for a single trait based on the selection differential (s) and the narrow-sense heritability (h2).

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Multivariate Breeder's Equation

An extension of the breeder's equation that accounts for the effects of selection on multiple correlated traits. It considers how selection on one trait can indirectly influence another trait due to their genetic relationship.

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Correlated Traits

Traits that are genetically linked and tend to be inherited together. Selection acting on one of these traits can indirectly affect the other.

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Phenotypic Variation (Vp)

The total observable differences in a trait among individuals within a population. It reflects the combined influence of genetics and environment.

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Additive Genetic Variance (Va)

The portion of genetic variance that directly contributes to offspring inheriting traits from their parents. It reflects the sum of the effects of individual genes.

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Dominance Genetic Variance (Vd)

The portion of genetic variance due to the interaction between alleles (alternative forms of a gene) at a single locus. It describes how dominant alleles mask the expression of recessive alleles.

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Genic Interaction Variance (Vi)

The portion of genetic variance due to interactions between alleles at different loci (gene locations). It reflects how genes work together to influence a trait.

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Genetic-Environmental Interaction (Vge)

The portion of phenotypic variation that results from the interaction between genetic and environmental factors. This implies that the expression of a gene can be influenced by the environment, and vice versa.

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Maternal Genetic Variance (Maternal VG)

The portion of genetic variance that is contributed by the mother. This can include factors like nutrients, hormones, and other maternal traits passed on to offspring.

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Maternal Environmental Variance (Maternal VE)

The portion of environmental variance that is contributed by the mother's environment. This includes things like the mother's diet, stress levels, or exposure to toxins.

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Epigenetic Variance

The portion of phenotypic variation that is due to changes in gene expression that do not involve changes in the DNA sequence. These modifications can be influenced by environmental factors and can be inherited.

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Study Notes

Evolutionary Biology - Lecture 13-14

  • Lecture covers phenotypic evolution, specifically focusing on the peppered moth ( Biston betularia).
  • The peppered moth exists in two color phases: light and dark.
  • Initially, light-colored moths were more common, camouflaging well against lichen-covered trees.
  • The industrial revolution brought air pollution, darkening trees with soot.
  • Dark-colored moths then became more prevalent due to better camouflage against the darkened trees.
  • Data from the mid-1800's show a drastic shift in moth coloration. -1848: 5% dark, 95% light -1895: 98% dark, 2% light -1995: 19% dark, 81% light
  • Bernard Kettlewell (1907-1979) conducted field studies in the 1950s to test the hypothesis that bird predators were altering moth coloration frequencies.
  • Kettlewell compared moth survival in polluted and unpolluted environments.
  • Results showed higher survival rates for dark moths in polluted areas and light moths in unpolluted areas.
  • Demonstrated natural selection based on predation as a mechanism of phenotypic evolution.
  • The typical white peppered moth phenotype is caused by a recessive allele (dd).
  • The melanic or black form is caused by a dominant allele.
  • The recessive allele (for white/light coloration) predominates in wild moth populations.
  • Air pollution controls introduced in the mid-1950s led to a decrease in the soot, and an increase in the frequency of the light-colored moths.
  • Industrial melanism is also observed in other moth species.
  • The goal of the lecture was to understand how morphological, physiological, and other biological characteristics evolve through natural selection.
  • Polygenic inheritance produces continuous variation in traits such as height and weight.
  • Traits such as height and other polygenic traits can be affected by environmental factors such as diet and exposure to UV light.
  • Traits are not independent of each other.
  • More interacting genes result in more variation in offspring, like in mouse coat colour variations.
  • Interactions between three or more genes (e.g., A, B, and C genes in mice) create a range of coat colour phenotypes.
  • A gene (e.g. A) can control the production of a particular feature, such as a band near the end of a hair.
  • The recessive allele of gene A gives a non-agouti (mousy) coat colour phenotype.
  • The B gene controls the basic coat colour(black).
  • The recessive allele for gene B causes a brown coat colour.
  • The C gene controls the expression of the other coat colour genes.
  • The recessive allele for gene C produces an albino phenotype

Polygenic Inheritance

  • Polygenic traits have a continuous range of phenotypes that follow a bell curve.
  • Fitness of individuals can vary from one end of the curve to another.
  • Natural selection on polygenic traits can affect the distributions of their phenotypes (shape of curve) in three ways: directional selection, stabilizing selection, and disruptive selection.

Measuring Heritability (h²)

  • Heritability is the proportion of total phenotypic variation that's due to genetic differences
  • Measuring heritability involves analyzing related individuals (e.g., twins, parents, offspring).
  • Parent-offspring regression analyses are used determine relationship between parent's phenotype and offspring's phenotype.
  • Breeder's equation (r = h²s) describes the response to directional selection.
  • The response is dependent on the narrow sense heritability (h²) and the selection differential (s)
  • s is the difference in the mean phenotype of the whole population before selection and mean of individuals actually breeding to produce the next generation.
  • This measures the change in phenotypes after natural selection is applied

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Description

This quiz explores the intricacies of polygenic traits and their expression in various environments. It delves into concepts such as continuous variation, natural selection, and the historical context of polygenic traits like the peppered moth. Additionally, it examines the relationship between genetic factors and environmental influences on phenotype.

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