Chapter 17 Flashcards
Microevolution
Small-scale genetic changes within populations, often in response to shifting environmental circumstances or chance events.
Population
All individuals of a single species that live together in the same place and time.
Heritable Phenotypic Variation
Differences in appearance or function between individual organisms that are passed from generation to generation.
Quantitative Variation
Variation that is measurable on a continuum (such as height) rather than in discrete units or categories (such as hair color).
Qualitative Variation
Variation that exists in two or more discrete states, with intermediate forms often being absent. For example, snow geese have white or blue feathers.
Polymorphism
The existence of qualitative traits. For example, snow geese are polymorphic in that they can be white or blue.
Describe the importance of genetic variation as the raw material for natural selection and evolution.
Organisms with genetic variations favourable to their survival in their environment will survive and reporduce and pass those traits onto their offspring resulting in natural selection/evolution.
Why is it important to determine whether the cause of phenotypic variation is environmental or genetic?
Provide a practical example.
Only genetic based variation is subject to evolutionary change.
For example, farmer may have two fields of corn that yield different amounts. Knowing if its environmental or genetic tells him how to tend his crops.
Identify the differences between genetic and environmental causes of genetic variation.
Because environmental factors can influence the expression of genes, an organism’s phenotype is frequently the product of an interaction between its genotype and its environment.
What are the potential sources for genetic variation?
The production of new alleles and the rearrangement of existing alleles.
What causes the production of the new alleles that provide a source for genetic variation?
Most likely small-scale mutations in DNA.
What causes the rearrangement of the existing alleles that provide a source for genetic variation?
Larger scale changes in chromosome structure or number and from several forms of genetic recombination, including crossing over between homologous chromosomes during meiosis, the independent assortment of nonhomologous chromosomes during meiosis, and random fertilizations between genetically different sperm and eggs.
Gene Pool
The sum of all alleles at all gene loci in all individuals in a population.
Locus
The particular site on a chromosome at which a gene is located.
Allele
One of two or more versions of a gene.
Genotype Frequency
The percentage of individuals in a population possessing a particular genotype.
How many alleles do diploid organisms have?
Two at each locus.
Allele Frequency
The abundance of one allele relative to others at the same gene locus in individuals of a population.
Relative Abundance
The relative commonness of populations within a community.
How are the frequencies of different alleles in diploid organisms identified?
For a locus with two alleles, scientists use the symbol p to identify the frequency of one allele, and q to identify the frequency of the other allele.
Herdy-Weinberg Principle
An evolutionary rule of thumb that specifies the conditions under which a population of diploid organisms achieves genetic equilibrium. It is a mathematical model that describes how genotype frequencies are established in sexually reproducing organisms.
Genetic Equilibrium
The point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations.
Outline the 5 conditions of the Hardy-Weinberg Principle.
- No mutations are occurring.
- The population is closed to migration from other populations.
- The population is infinite in size.
- All genotypes in the population survive and reproduce equally well.
- Individuals in the population mate randomly with respect to genotypes.
Why is the Hardy-Weinberg Principle considered a null model of evolution?
Null models predict what would be seen if a particular factor had no effect.
According to this model, genetic equilibrium is possible only if all of its conditions are met. If the conditions of the model are met, the allele frequencies of the population will never change, and the genotype frequencies will stop changing after one generation. In short, under these restrictive conditions, microevolution will not occur. The Hardy–Weinberg principle is thus a null model that serves as a reference point for evaluating the circumstances under which evolution may occur.
What processes foster microevolutionary change?
Mutation, gene flow, genetic drift, natural selection, and nonrandom mating.
Mutation
A spontaneous and heritable change in DNA.
Why are mutations a major source of genetic variations in populations?
Because it is a mechanism through which entirely new genetic variations arise.
Gene Flow
Change in allele frequencies as individuals join a population and reproduce.
What are the effects of gene flow on genetic variation?
May introduce genetic variation from another population.
Genetic Drift
Random changes in allele frequencies caused by chance events.
What are the effects of genetic drift on genetic variation?
Reduces genetic variation, especially in small populations; can eliminate alleles.
Natural Selection
The evolutionary process by which alleles that increase the likelihood of survival and the reproductive output of the individuals that carry them become more common in subsequent generations.
What are the effects of natural selection on genetic variation?
One allele can replace another or allelic variation can be preserved.
Nonrandom Mating
Choice of mates based on their phenotypes and genotypes.
What are the effects of nonrandom mating on genetic variation?
Does not directly affect allele frequencies, but usually prevents genetic equilibrium.
Biological Lineage
An evolutionary sequence of ancestral organisms and their descendants.
Why are mutations a major source of genetic variation in populations?
Because they have been accumulating in biological lineages for billions of years and because it is a mechanism through which entirely new genetic variations arise, making it a major source of heritable variation.
Deleterious Mutations
Alter an individual’s structure, function, or behaviour in harmful ways.
What are the types of mutations?
Deleterious
Lethal
Neutral
Advantageous
Describe the importance of gene flow.
The evolutionary importance of gene flow depends on the degree of genetic differentiation between populations and the rate of gene flow between them. If two gene pools are very different, a little gene flow may increase genetic variability within the population that receives immigrants, and it will make the two populations more similar. But if populations are already genetically similar, even a lot of gene flow will have little effect.
Why does genetic drift reduce genetic variation in populations?
Since genetic drift most commonly occurs in small populations it generally leads to the loss of alleles and reduced genetic variability.
Population Bottleneck
An evolutionary event that occurs when a stressful factor reduces population size greatly and eliminates some alleles from a population. For example, disease, starvation, drought, overhunting.
Founder Effect
An evolutionary phenomenon in which a population that was established by just a few colonizing individuals has only a fraction of the genetic diversity seen in the population from which it was derived.
Conservation Biology
An interdisciplinary science that focuses on the maintenance and preservation of biodiversity.
How are endangered species related to genetic drift?
Endangered species experience severe population bottlenecks, which result in the loss of genetic variability. Moreover, the small number of individuals available for captive breeding programs may not fully represent a species’ genetic diversity. Without such variation, no matter how large a population may become in the future, it will be less resistant to diseases or less able to cope with environmental change.
Relative Fitness
The number of surviving offspring that an individual produces compared with the number left by others in the population.
What are the types of natural selection?
Directional
Stabilizing
Disruptive
Directional Selection
A type of selection in which individuals near one end of the phenotypic spectrum have the highest relative fitness.
Stabilizing Selection
A type of natural selection in which individuals expressing intermediate phenotypes have the highest relative fitness.
Disruptive Selection
A type of natural selection in which extreme phenotypes have higher relative fitness than intermediate phenotypes which can result in polymorphisms.
Sexual Selection
A form of natural selection established by male competition for access to females and by the females’ choice of mates.
Sexual Dimorphism
Differences in the size or appearance of males and females.
Intersexual Selection
Selection based on the interactions between males and females.
Intrasexual Selection
Selection based on the interactions between members of the same sex such as males using their large body size, antlers, or tusks to intimidate, injure, or kill rival males.
Inbreeding
A special form of nonrandom mating in which genetically related individuals mate with each other.
Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
p = dominant allele
q = recessive allele
Homozygous
State of possessing two copies of the same allele.
Heterozygous
The state of possessing two different alleles of a gene.
How is genetic variation maintained through diploidy?
The recessive allele is masked by the dominant allele therefore even though it may not be best for natural selection, it is still passed to other generations.
Balanced Polymorphism
The maintenance of two or more phenotypes in fairly stable proportions over many generations.
When do balanced polymorphisms generally occur?
Natural selection preserves balanced polymorphisms when heterozygotes have higher relative fitness, when different alleles are favoured in different environments, and when the rarity of a phenotype provides an advantage.
Heterozygote Advantage
An evolutionary circumstance in which individuals that are heterozygous at a particular locus have higher relative fitness than either homozygote.
How does the environment maintain genetic variation?
When different alleles are favoured in different places or at different times.
Frequency-Dependent Selection
A form of natural selection in which rare phenotypes have a selective advantage simply because they are rare.
Neutral Variation Hypothesis
An evolutionary hypothesis that some variation at gene loci coding for enzymes and other soluble proteins is neither favoured nor eliminated by natural selection. They are therefore selectively neutral.
Adaptation
Characteristic or suite of characteristics that helps an organism survive longer or reproduce more under a particular set of environmental conditions.
A result of natural selection.
Adaptive Trait
A genetically based characteristic, preserved by natural selection, that increases an organism’s likelihood of survival or its reproductive output.
Why aren’t adaptations perfect?
Natural selection cannot result in perfectly adapted organisms because most adaptive traits represent compromises among conflicting needs; because most environments are constantly changing; and because natural selection can affect only existing genetic variation.
Artificial Selection
Selective breeding of animals or plants to ensure that certain desirable traits appear at higher frequency in successive generations.
