Introduction to Genetics and Evolution

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Questions and Answers

How do phenotype and genotype differ in the context of natural selection?

Genotype refers to the genetic makeup of an organism, while phenotype is the expressed traits resulting from that genotype. Natural selection acts on phenotypes, influencing their reproductive success, which can change allele frequencies in a population.

Explain the process and outcome of stabilizing selection using an example.

Stabilizing selection promotes average traits and eliminates extremes, leading to reduced trait variation. An example is the optimal human birth weight of 3-4 kg, where weights outside this range are associated with higher risks of complications.

What is directional selection, and how does it influence trait evolution?

Directional selection favors one extreme trait, leading to gradual changes in that trait over time. For instance, lighter skin became advantageous for vitamin D production in populations migrating to areas with less sunlight.

Describe how gene flow can impact the allele frequencies in a population.

<p>Gene flow occurs when individuals migrate and breed in new locations, introducing new alleles into the gene pool. This can increase genetic diversity and alter allele frequencies, potentially enhancing evolutionary change.</p> Signup and view all the answers

What is meant by genetic drift, and what can be its consequences?

<p>Genetic drift is the random change in allele frequencies, especially in small populations, which can lead to decreased genetic diversity. It may result in the loss of advantageous alleles and fixation of harmful ones.</p> Signup and view all the answers

Clarify the concept of the founder effect and its implications for a new population.

<p>The founder effect occurs when a small group colonizes a new area, leading to a limited gene pool that defines the new population. This can decrease genetic diversity and increase the likelihood of inbreeding and genetic disorders.</p> Signup and view all the answers

How do environmental factors influence the mechanisms of natural selection?

<p>Environmental factors affect reproductive success by favoring certain traits that enhance survival. These changes in trait fitness can lead to shifts in allele frequencies, driving evolutionary changes in populations.</p> Signup and view all the answers

Discuss the role of natural selection in speciation processes.

<p>Natural selection can lead to speciation by promoting the divergence of traits in populations subjected to different environmental pressures, ultimately resulting in reproductive isolation. This divergence can lead to the formation of new species over time.</p> Signup and view all the answers

What is the primary difference between phenotype and genotype?

<p>The genotype refers to the genetic makeup of an organism, while the phenotype is the observable characteristics resulting from that genotype.</p> Signup and view all the answers

What type of selection favors intermediate phenotypes and reduces variation?

<p>Stabilizing selection favors intermediate phenotypes and reduces phenotypic variation.</p> Signup and view all the answers

In directional selection, how does the population's traits shift over time?

<p>Directional selection causes the population's traits to shift towards one extreme of a trait spectrum.</p> Signup and view all the answers

What is disruptive selection and how does it affect phenotypic variation?

<p>Disruptive selection favors individuals at both extremes of a trait spectrum, increasing phenotypic variation.</p> Signup and view all the answers

How did Gregor Mendel contribute to the understanding of inheritance?

<p>Gregor Mendel established foundational principles of inheritance through his experiments with pea plants, demonstrating how traits are passed from parents to offspring.</p> Signup and view all the answers

What are the four main mechanisms of natural selection described by Darwin?

<p>The four main mechanisms of natural selection are overproduction, competition, variation, and survival of the fittest.</p> Signup and view all the answers

What process is described by 'descent with modification' in Darwin's theory of evolution?

<p>'Descent with modification' refers to the gradual change in populations over time, leading to the development of new species from common ancestors.</p> Signup and view all the answers

Define speciation and its significance in the context of evolution.

<p>Speciation is the evolutionary process through which new biological species arise, important because it contributes to biodiversity and the adaptation of organisms.</p> Signup and view all the answers

What is the primary difference between phenotype and genotype?

<p>Phenotype refers to the physical expression of a trait, while genotype refers to the genetic constitution of an individual.</p> Signup and view all the answers

Explain the concept of disruptive selection with an example.

<p>Disruptive selection favors individuals at both extremes of a trait distribution; for example, small-billed and large-billed birds thrive while medium-billed birds struggle to survive.</p> Signup and view all the answers

How does stabilizing selection differ from disruptive selection?

<p>Stabilizing selection favors intermediate phenotypes, reducing variation, whereas disruptive selection favors extreme phenotypes, leading to increased variation.</p> Signup and view all the answers

What role did Gregor Mendel play in the development of genetics?

<p>Gregor Mendel is known as the father of modern genetics for his experiments with garden peas, which established the fundamental laws of inheritance.</p> Signup and view all the answers

Define speciation and explain one mechanism by which it occurs.

<p>Speciation is the process by which new species are formed; it can occur through reproductive isolation due to geographic barriers.</p> Signup and view all the answers

What is an allele, and how does it relate to the concepts of dominant and recessive traits?

<p>An allele is a version of a gene, with dominant alleles expressing the trait over recessive alleles, which are masked in the presence of a dominant partner.</p> Signup and view all the answers

Describe the significance of Mendel's filial generation (F1) in understanding inheritance.

<p>The filial generation (F1) represents the offspring of the parental generation (P), demonstrating how traits are inherited from one generation to the next.</p> Signup and view all the answers

What is the importance of genotype homozygotes and heterozygotes in Mendelian genetics?

<p>Homozygotes have identical alleles for a trait, while heterozygotes have two different alleles, influencing the trait's expression and inheritance.</p> Signup and view all the answers

How did Leeuwenhoek and de Graaf contribute to the understanding of inheritance?

<p>They discovered sperm and ova, highlighting that both males and females contribute to inheritance.</p> Signup and view all the answers

What gap in understanding did Gregor Mendel's work address in the context of evolution?

<p>Mendel's work provided genetic insight that Darwin's theory of evolution by natural selection lacked.</p> Signup and view all the answers

Explain the role of 'Survival of the Fittest' in Darwin's theory of evolution.

<p>'Survival of the Fittest' refers to individuals with advantageous traits being more likely to survive and reproduce.</p> Signup and view all the answers

What does the term 'adaptation' signify in the context of evolution?

<p>Adaptation refers to inherited traits that enhance an organism's survival and reproductive success.</p> Signup and view all the answers

Describe how evolution is connected to the chromosome theory of inheritance.

<p>The chromosome theory explains that genes on chromosomes dictate inherited traits, linking genetics to evolution.</p> Signup and view all the answers

What is meant by 'descent with modification' in evolution?

<p>'Descent with modification' refers to the gradual changes in species over time, leading to new species from common ancestors.</p> Signup and view all the answers

How does competition among individuals within a population influence evolution?

<p>Competition leads to the survival of individuals with advantageous traits, driving evolutionary change.</p> Signup and view all the answers

What is the significance of phenotypic variation in a population regarding natural selection?

<p>Phenotypic variation provides the raw material for natural selection, allowing advantageous traits to be favored.</p> Signup and view all the answers

How does fitness influence allele frequency in a population?

<p>Higher fitness increases the likelihood of passing genes to future generations, thereby altering allele frequency.</p> Signup and view all the answers

What impact can a population bottleneck have on genetic diversity?

<p>A population bottleneck can significantly reduce genetic diversity by limiting the number of individuals contributing to the gene pool.</p> Signup and view all the answers

In what way does gene flow affect a population's genetic composition?

<p>Gene flow introduces new alleles into the gene pool, which can change allele frequencies within the population.</p> Signup and view all the answers

How does stabilizing selection maintain a population's trait distribution?

<p>Stabilizing selection favors intermediate traits, reducing the prevalence of extremes and keeping the population centered around an optimal trait value.</p> Signup and view all the answers

What is the founder effect and how does it relate to genetic variation?

<p>The founder effect occurs when a small group colonizes a new area, leading to reduced genetic variation due to a limited allele pool.</p> Signup and view all the answers

Describe how directional selection has influenced human skin color adaptation.

<p>Directional selection has favored lighter skin in populations migrating to areas with lower sunlight, enhancing vitamin D production.</p> Signup and view all the answers

What role does genetic drift play in small populations?

<p>Genetic drift can lead to the loss of genetic diversity and fixation of harmful alleles, impacting the overall adaptability of small populations.</p> Signup and view all the answers

How do environmental factors contribute to the process of natural selection?

<p>Environmental factors influence reproductive success, determining which traits are favored or selected against in a population.</p> Signup and view all the answers

How does disruptive selection lead to the emergence of two distinct phenotypes in a population?

<p>Disruptive selection favors individuals at both extremes of a trait, like small-billed and large-billed birds, resulting in reduced survival for intermediate phenotypes.</p> Signup and view all the answers

What was one of the significant weaknesses in Darwin's theory of evolution?

<p>Darwin lacked a scientific understanding of the mechanism of inheritance, which left his theory susceptible to critique.</p> Signup and view all the answers

Explain how the geographical isolation of a population can contribute to speciation.

<p>Geographical isolation prevents gene flow between populations, allowing for different traits to become dominant and leading to the formation of new species.</p> Signup and view all the answers

In Mendelian genetics, what is the difference between homozygotes and heterozygotes?

<p>Homozygotes have two identical alleles for a trait, while heterozygotes carry one dominant and one recessive allele.</p> Signup and view all the answers

Describe the significance of Mendel's experiments with Pisum sativum in the context of genetics.

<p>Mendel's experiments established fundamental laws of inheritance by demonstrating how traits are passed through discrete units, now known as genes.</p> Signup and view all the answers

What technique did Mendel use to ensure controlled pollination in his experiments?

<p>Mendel used manual techniques such as removing male parts and hand pollination.</p> Signup and view all the answers

What are alleles, and how do they relate to dominant and recessive traits?

<p>Alleles are different versions of a gene, and a dominant allele will express its trait over a recessive allele, which is masked in its presence.</p> Signup and view all the answers

How did Mendel's identification of filial generations contribute to the field of genetics?

<p>Mendel's study of filial generations, notably F1 and F2, revealed predictable patterns of inheritance that are central to genetic theory.</p> Signup and view all the answers

What is the phenotypic ratio expected from a monohybrid cross between two heterozygous parents (Aa × Aa)?

<p>The expected phenotypic ratio is 3:1, with three exhibiting the dominant trait and one the recessive trait.</p> Signup and view all the answers

What role does the location of a gene (locus) play in genetics?

<p>The locus is the specific location of a gene on a chromosome, essential for identifying alleles and understanding genetic variation.</p> Signup and view all the answers

How did Mendel simplify the analysis of inheritance patterns in his experiments?

<p>Mendel focused on binary traits, ensuring that traits were inherited similarly in both sexes, which simplified his observations.</p> Signup and view all the answers

Explain the Principle of Dominance as discovered by Mendel.

<p>The Principle of Dominance states that in a pair of alleles, one can mask the expression of the other.</p> Signup and view all the answers

What was the significance of Mendel's work in the foundation of genetics?

<p>Mendel's experiments laid the groundwork for the laws of inheritance and the concepts of dominant and recessive traits.</p> Signup and view all the answers

What ratio arises in the offspring from a cross between a homozygous dominant and a homozygous recessive parent (AA × aa)?

<p>All offspring will be heterozygous (Aa), showing the dominant phenotype.</p> Signup and view all the answers

Describe the role of pollination in plant reproduction as studied by Mendel.

<p>Pollination is the transfer of pollen from the male parts to the female parts of a flower, essential for fertilization.</p> Signup and view all the answers

What is the result of a cross between two homozygous recessive plants (aa × aa)?

<p>All offspring will be homozygous recessive (aa).</p> Signup and view all the answers

What does the Principle of Segregation state regarding allele distribution in gametes?

<p>It states that during gamete formation, the two alleles for a trait separate so that each gamete receives only one allele.</p> Signup and view all the answers

How does a Test Cross help determine the genotype of an individual expressing a dominant trait?

<p>A Test Cross involves crossing the individual with a homozygous recessive to observe the offspring, determining if the individual is homozygous dominant or heterozygous.</p> Signup and view all the answers

What is the significance of Mendel's findings in the F2 generation regarding trait inheritance?

<p>Mendel found that both dominant and recessive traits reappeared in the F2 generation, disproving the blending inheritance theory.</p> Signup and view all the answers

Define a dihybrid cross and explain its importance in genetic studies.

<p>A dihybrid cross examines the inheritance of two different genes, each with two alleles, which helps understand the principle of independent assortment.</p> Signup and view all the answers

In genetic terms, what does it mean for an organism to be homozygous recessive?

<p>An organism is homozygous recessive if it has two copies of the recessive allele, resulting in the expression of the recessive phenotype.</p> Signup and view all the answers

What does the Punnett square demonstrate in the study of genetics?

<p>The Punnett square predicts the possible genotypes of offspring based on the gametes of the parents by showing how alleles combine.</p> Signup and view all the answers

Explain what is meant by 'dominance' in the context of alleles.

<p>Dominance refers to the phenomenon where the presence of a dominant allele masks the expression of a recessive allele in a heterozygous organism.</p> Signup and view all the answers

How does meiosis contribute to genetic diversity in diploid organisms?

<p>Meiosis creates haploid gametes by separating homologous chromosomes, allowing for a mix of parental alleles in the offspring.</p> Signup and view all the answers

What is the phenotypic ratio of the F2 generation resulting from a dihybrid cross between two WwGg pea plants?

<p>The phenotypic ratio is 9:3:3:1.</p> Signup and view all the answers

In the context of incomplete dominance, what phenotype is produced in the F1 generation when crossing dark purple (PP) and white (pp) plants?

<p>The F1 generation displays a light purple phenotype.</p> Signup and view all the answers

Define codominance and provide an example of a trait that exhibits this pattern of inheritance.

<p>Codominance occurs when both alleles are fully expressed; an example is human blood type AB.</p> Signup and view all the answers

What do the gametes produced by heterozygous WwGg plants consist of, and how many different types are produced?

<p>The gametes consist of WG, Wg, wG, and wg, totaling four types.</p> Signup and view all the answers

What is incomplete penetrance and how might it affect the expression of a dominant allele?

<p>Incomplete penetrance occurs when a dominant allele does not always manifest in the phenotype.</p> Signup and view all the answers

In Gregor Mendel's dihybrid cross, what are the recombinant phenotypes observed in the F2 generation?

<p>The recombinant phenotypes are wrinkled yellow and wrinkled green.</p> Signup and view all the answers

Explain the concept of true breeding using the genotypes WWGG and wwgg in pea plants.

<p>True breeding refers to organisms that consistently produce offspring with a specific phenotype, such as WWGG for smooth yellow seeds.</p> Signup and view all the answers

How did Mendel's findings on dominance and recessiveness influence the understanding of genetic inheritance?

<p>Mendel established that dominant alleles completely mask recessive alleles, forming the foundation of classical genetics.</p> Signup and view all the answers

Flashcards

Allele

A variant form of a gene on a chromosome.

Gene Pool

The total number of alleles in a population.

Fitness

Reproductive success of an organism's genotype or phenotype.

Allele Frequency

The relative proportion of a specific allele in a population.

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Natural Selection

Environment influencing reproductive success based on traits.

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Gene Flow

Migration and breeding introducing new alleles.

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Genetic Drift

Factors reducing genetic diversity in small populations.

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Population Bottleneck

Few individuals influence gene pool, reducing genetic diversity.

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Founder Effect

Small group colonizing a new area, impacting population genetics.

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Stabilizing Selection

Selection favoring traits in the middle range, reducing variation.

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Directional Selection

Favors one extreme trait, leading to gradual change.

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Disruptive Selection

Natural selection that favors individuals at both extremes of a trait. This leads to two distinct phenotypes.

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Inheritance

The passing of traits from parents to offspring.

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Adaptation

A trait that helps an organism survive and reproduce.

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Allele

One of the versions of a gene.

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Dominant Allele

An allele that produces the observed trait.

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Natural Selection

Organisms with advantageous traits are more likely to survive and reproduce.

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Evolution

Gradual genetic change within a population, leading to phenotypic variation.

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Recessive Allele

An allele that is masked by a dominant allele.

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Heterozygote

An individual with one dominant and one recessive allele for a gene.

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Overproduction

Organisms produce more offspring than can survive due to limited resources.

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Competition

Individuals in a population struggling for limited resources.

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Homozygote

An individual with two identical alleles for a gene.

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Variation

Differences in traits within a population, some beneficial for survival.

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Gene

An inherited factor that determines a trait; a segment of DNA.

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Survival of the Fittest

Individuals with the most advantageous traits are more likely to survive and reproduce.

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Genotype

The genetic makeup of an organism.

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Fitness

An individual's ability to survive and reproduce in a given environment.

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Phenotype

The physical expression of a trait.

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Locus

The specific location of a gene on a chromosome.

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Descent with Modification

Species gradually change over time, potentially leading to new species from common ancestors.

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Chromosome Theory of Inheritance

Linking genetics to evolution, explaining how traits are passed on and evolve.

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Parental Generation (P)

The initial generation in a genetic cross.

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Filial Generation (F n)

Offspring generations of a genetic cross.

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Natural Selection

The process where organisms with advantageous traits are more likely to survive and reproduce, leading to changes in a population over time.

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Overproduction

Organisms produce more offspring than can possibly survive due to limited resources.

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Competition

Individuals in a population compete for limited resources like food and space.

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Variation

Differences in traits (e.g., size, color) within a population.

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Survival of the Fittest

Individuals with traits best suited to the environment are more likely to survive and reproduce.

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Adaptation

Inherited trait that enhances survival and reproduction in a specific environment.

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Evolution

Gradual genetic change within a population, resulting in phenotypic variation over time.

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Inheritance

Passing of traits from parents to offspring.

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Descent with Modification

Species change over time and new species arise from common ancestors.

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Chromosome Theory of Inheritance

Link between genetics and evolution, explaining how traits are passed and evolve.

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Evolutionary Change

Change in allele frequency within a gene pool over time

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Allele Frequency

The proportion of a particular allele in a population.

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Fitness

Reproductive success relative to other individuals in a population.

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Natural Selection

Environmental factors influencing an organism's reproductive success based on traits.

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Gene Flow

Introduction of new alleles into a gene pool through migration and breeding.

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Genetic Drift

Evolutionary change caused by random factors in small populations.

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Population Bottleneck

Reduced genetic diversity due to a significant reduction in population size.

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Founder Effect

Limited genetic variation in a new population established by a small group of founders.

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Stabilizing Selection

Natural selection favoring traits in the middle range and reducing variation.

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Directional Selection

Natural selection favoring one extreme trait, leading to a shift in the population.

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Monohybrid Cross

A genetic cross that focuses on the inheritance of a single trait.

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Dominant Trait

A trait that is expressed when only one copy of the gene is present.

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Recessive Trait

A trait that is only expressed when two copies of the gene are present.

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Controlled Pollination

Manually transferring pollen between plants to control which traits are passed on

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Homozygous

Having two identical alleles for a gene.

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Heterozygous

Having two different alleles for a gene.

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Principle of Dominance

One allele can mask the expression of another allele.

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Pollination

The transfer of pollen from the male to the female parts of a flower.

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Fertilization

The joining of sperm and egg to form a zygote.

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Disruptive Selection

Natural selection that favors individuals at both extremes of a trait, leading to two distinct phenotypes.

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Allele

One of the versions of a gene.

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Dominant Allele

An allele that produces the observed trait.

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Recessive Allele

An allele that is masked by a dominant allele.

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Gene

An inherited factor that determines a trait; a segment of DNA.

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Genotype

The genetic makeup of an organism.

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Phenotype

The physical expression of a trait.

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Locus

The specific location of a gene on a chromosome.

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Heterozygote

An individual with one dominant and one recessive allele for a gene.

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Homozygote

An individual with two identical alleles for a gene.

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Parental Generation (P)

The initial generation in a genetic cross.

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Filial Generation (F n)

Offspring generations of a genetic cross.

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Dominant Trait

A trait that appears in the offspring when only one dominant allele is present.

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Recessive Trait

A trait that only appears when two copies of the recessive allele are present.

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Homozygous

Having two identical alleles for a specific gene.

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Heterozygous

Having two different alleles for a specific gene.

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Punnett Square

A grid used to predict possible genotypes of offspring from a genetic cross.

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Segregation

Separation of alleles from each parent during gamete formation.

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Test Cross

A cross used to determine the genotype of an individual with a dominant phenotype.

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Dihybrid Cross

A genetic cross involving two pairs of traits.

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Dihybrid Cross

A genetic cross involving two traits with differing alleles controlled by two different gene pairs.

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Smooth Yellow Seeds

A phenotype in pea plants exhibiting smooth seed shape and yellow seed color, a combination of dominant traits.

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Wrinkled Green Seeds

A phenotype in pea plants exhibiting wrinkled seed shape and green seed color, both recessive traits.

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F1 Generation

The first generation of offspring produced from a cross of two parental (P) generation organisms.

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F2 Generation

The second generation of offspring resulting from a genetic cross of F1 generation organism.

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Incomplete Dominance

A pattern of inheritance where the heterozygote's phenotype is an intermediate blend of the two homozygous phenotypes.

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Codominance

A pattern of inheritance where both alleles in a heterozygote are fully expressed, leading to a phenotype that represents both.

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Incomplete Penetrance

A situation where the dominant allele may not always manifest in the phenotype.

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Recessive Allele

An allele that is expressed only when two copies are present.

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Study Notes

Introduction to Genetics

  • Genetics' origins trace back to ancient civilizations, but scientific study began in the 17th century.
  • Both males and females contribute to inheritance.
  • Darwin's theory of evolution lacked genetic insight.
  • Mendel's research on peas established modern genetics.
  • Genetics is linked to evolution, explaining trait inheritance and change over time.

Adaptation and Evolution

  • Adaptation enhances an organism's survival and reproduction, influenced by inherited traits and environmental pressures.
  • Evolution is a gradual genetic change within a population.
  • Darwin's theory of evolution by natural selection emphasizes:
    • Organisms produce more offspring than the environment can support, resulting in competition for resources
    • Individuals vary in traits influencing survival and reproduction.
    • Individuals with advantageous traits that enhance survival and reproduction are more likely to succeed and pass on their traits.
    • Survival of the fittest: Individuals with the best traits for their environment are more likely to survive and reproduce

Mechanisms of Natural Selection

  • Natural selection favors certain traits that increase in proportion within a population.
  • Stabilizing selection favors traits in the middle range, eliminating extremes.
  • Example: human birth weight; optimal range is 3–4kg
  • Directional selection shifts the population towards a specific trait over time.
    • Example: Humans migrating to regions with less sunlight, darker skin became less advantageous, and lighter skin became favored.
  • Disruptive selection favors both extremes, resulting in two distinct phenotypes. Example: birds with small or large beaks.

Gregor Mendel— A Foundation for Genetics

  • Mendel's work established the foundation for understanding inheritance.
  • Mendel's experiments focused on pea plants.
  • Traits among pea plants do not blend, but maintain an identifiable presence.
  • He tracked traits across seven generations.

Mendel's Work with Peas

  • Mendel's experiments focused on traits controlled by a single gene.
  • Mendel used true-breeding plants for his studies.
  • Mendel's controlled breeding experiments revealed the following:
    • Law of Uniformity: offspring of two homozygotes with different alleles will all have identical heterozygous traits.
    • The Law of Segregation: each parent contributes one allele for a trait to their offspring.
    • The Law of Independent Assortment: traits sort independently of one another during reproduction.

Monohybrid Crosses

  • Mendel crossed true-breeding plants with differing traits.
  • A monohybrid cross only studies one gene and its two alleles, with one allele being dominant and one recessive.
  • The dominant trait will mask the expression of the recessive trait in the first generation.
  • Example of Dominant traits in heterozygotes: Tall (T) is dominant over Short (t), Round (R) seeds are dominant over wrinkled (r) seeds, and Yellow (Y) seed color is dominant over green (y).

Principle of Dominance

  • In heterozygotes, one allele may mask the effect of another (dominant vs. recessive).

Principle of Segregation

  • Each individual carries two alleles for a trait, only one of which is passed on to each offspring.
  • During gamete formation, the two alleles separate, ensuring each gamete receives only one allele.

Dihybrid Crosses

  • Dihybrid crosses involve considering two different genes, each with two alleles.
  • Example: seed shape and seed color
  • The number of possible combinations increase based on how many alleles are present in the crossed individual(s).

Complex Inheritance Patterns

  • Incomplete dominance: heterozygotes have an intermediate phenotype between two homozygous phenotypes (i.e., a mix of both phenotypes).
  • Example: light purple eggplant from a dark purple and white parents.
  • Codominance: both alleles in a heterozygote are fully expressed.
    • Example: human blood types (Type A, Type B, Type AB).
  • Incomplete penetrance: dominant alleles may fail to express the dominant trait in every individual.
  • Example: mutations in BRCA1 increase the risk of breast and ovarian cancer, but don't guarantee the disease.

Complications in Inheritance

  • Multiple alleles: multiple alleles at a single locus complicate inheritance patterns.
  • Example: rabbit coat colors.
  • Lethal alleles: some alleles, when present in homozygous form, can prevent survival.
  • Example: yellow coat in mice.
  • Gene interactions: many phenotypes result from a combined inheritance from interacting genes.
  • Epistasis: one gene masks the expression of another gene.
  • Pleiotropy: a single gene leads to seemingly unrelated phenotypes.
    • Example: Phenylketonuria (PKU)

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