Ch.17

Question 1

Bottleneck events

Answer 1

Events that cause a sudden drop in population size are called bottlenecks and are of concern because, along with low numbers, there is also a decrease in genetic diversity of the population.

Small populations that are the result of bottlenecks with low genetic diversity are much more susceptible to disease and have limited ability to survive unfavourable environmental changes.

The large reduction in population size is associated with a decrease in the size of the gene pool and, therefore, the genetic diversity of the population. Alleles that were rare in the original population can be totally lost from the population in the event of a bottleneck

Question 2

Microevolution

Answer 2

Involves looking at changes in the genetic make-up (the genotype) of populations of a species over time. Microevolution can fine-tune the functioning of populations within their environments.

Today, microevolutionary studies often begin by assessing the extent of phenotypic variation within populations. variations in their individual biochemistry, physiology, internal anatomy, and behaviour. All these features are examples of phenotypic variation—differences in appearance or function

Genetic drift, mutation, gene flow, and natural selection all can change allele frequencies of a population and thus drive evolutionary change. However, it is only natural selection that consistently improves the ability of a population to grow and reproduce in a particular environment, that is, to adapt. The other evolutionary processes do not always result in a population developing increased fitness in a particular environment over time. As well, it is important to remember that microevolutionary processes do not work in isolation of one another. For example, by itself, a rare beneficial mutation to one individual in a population will do little to change allele frequencies, but they can change appreciably after the population is acted upon by natural selection.

Question 3

qualitative variation

Answer 3

—they exist in two or more discrete states, and intermediate forms are absent.

Question 4

quantitative variation

Answer 4

Most characters exhibit quantitative variation—individuals differ in small, incremental ways.

For example, humans exhibit quantitative variation in the length of their toes, the number of hairs on their heads, and their height.

The existence of discrete variants of a character is called a polymorphism, we describe such traits as polymorphic. We describe phenotypic polymorphisms quantitatively by calculating the frequency of each trait.

Question 5

Phenotypic variation

Answer 5

Variation within populations may be caused by genetic differences between individuals. But it can also be caused solely by environmental factors that individuals experience, or by an interaction between genetics and the environment. As a result, genetic and phenotypic variations may not be perfectly correlated.

Under some circumstances, organisms with different genotypes exhibit the same phenotype. Conversely, organisms with the same genotype sometimes exhibit different phenotypes.

Knowing whether phenotypic variation is caused by genetic differences, environmental factors, or an interaction of the two is important because only genetically based variation is inherited and thus subject to evolutionary change.

Moreover, knowing the causes of phenotypic variation has important practical applications. How can we determine whether phenotypic variation is caused by environmental factors or genetic differences? We can test for an environmental cause experimentally by changing one environmental variable and measuring the effects on genetically similar subjects.

Must be heritable to contribute to evolution.

Question 6

population genetics

Answer 6

is distinct in that it focuses on the genetic variation that exists within a population and how this changes over time as a result of evolution.

To predict how certain factors may influence genetic variation, population geneticists first describe the genetic structure of a population. They then create and test hypotheses, formalized in mathematical models, to describe how evolutionary processes may change the genetic structure under specified conditions.

Question 7

evolution

Answer 7

is a change in allele frequencies from one generation to the next. Changing how common a particular allele is within a population (its frequency) changes the genetic makeup of the population.

Evolution can in fact be caused by four distinct processes: mutation, genetic drift, gene flow, and natural selection.(these change the frequency of alleles) understanding that each of these processes acting alone or in combination has the ability to change the traits in a population over time—each one can drive evolutionary change.

Question 8

Gene pool

Answer 8

• the sum of all alleles at all loci in a population.

The total genetic variability of a population is represented by all the alleles at all the gene loci in all individuals within the population and is referred to as the gene pool. Can also refer to frequency of alleles of one locus within a population.

You may think that the genetic variation that exists in a population is because individuals of the same species have different genes. But that is not exactly right. Rather, the genetic variation is because individuals possess different versions of the same genes. That is, different individuals may carry different alleles for one or more genes

Question 9

Genetic variation

Answer 9

the raw material of evolutionary change has two potential sources:
(1) the production of new alleles
(2) the rearrangement of existing alleles into new combinations.

New alleles arise from processes that introduce changes to the actual DNA sequence. As well, genetic variation can come about by changing the arrangement of alleles along a chromosome. Caused by genetic recombination during meiosis. This shuffling of alleles into new combinations can produce an extraordinary number of novel genotypes in the next generation.

A major area of research is the study of single-nucleotide polymorphisms (SNPs, also called “snips”). These single-nucleotide differences can exist between individuals and have been shown to account for about 90% of the genetic variation found in humans.

Question 10

null hypothesis

Answer 10

is a prediction of what researchers would see if that particular factor had no effect.

Question 11

Hardy-Weinberg principle

Answer 11

An evolutionary rule of thumb that specifies the conditions under which a population of diploid organisms achieves genetic equilibrium- The point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations. Possible only if all the following conditions are met:
(1) The population is closed to migration from other populations.
(2) The population is infinite in size.
(3) No mutation is occurring in the population.
(4) All genotypes in the population survive and reproduce equally well.
(5) Individuals in the population mate randomly with respect to genotype.

Formulated independently by Godfrey Harold Hardy (British mathematician) and William Weinberg (German physician) in 1908.

Question 12

Gene flow

Answer 12

The transfer of genes from one population to another through the movement of individuals or their gametes.violates Hardy-Weinberg (condition 1). Must be closed to migration.

The importance of gene flow in driving evolutionary change within a population depends on how different the gene pool is between it and other populations and the rate of gene flow into and out of the population. Since the environmental conditions and thus selection experienced by two populations will not be identical, the flow of new alleles into a population may alter its fitness. As you would expect, the exchange of alleles between two populations will decrease the genetic differences between the populations, making them more similar.

Question 13

Genetic drift

Answer 13

Random fluctuations in allele frequencies as a result of chance events; usually reduces genetic variation in a population. Can have a major impact on allele frequencies, especially in small populations. Generally leads to reduced genetic diversity in small populations because rare alleles are often lost. violates the Hardy–Weinberg assumption of infinitely large population size (Condition 2).

Genetic drift is driven by two circumstances: founder effects and population bottlenecks.

What’s important to realize is that, regardless of how large the population ends up being, it will still be based on a gene pool that will remain small. Endangered species can be protected from extinction, but the lack of genetic variability would suggest that the population will always be more susceptible to disease and less able to cope with environmental perturbations such as climate change.

Question 14

Founder effect

Answer 14

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.

Question 15

Mutation

Answer 15

A mutation is a change to the double-strand sequence of DNA. Common factors that cause mutation include radiation (e.g., UV light), which can actually damage individual nucleotides, and some hazardous chemicals that can interfere with DNA replication. However, most mutations are not caused by some environmental factor, but occur as a result of normal cellular processes. This includes errors in copying DNA during DNA replication as well as the movement of transposable elements from one place in the genome to another. (condition 3). There are five basic types of mutation:

Point mutation: A single nucleotide (base) is changed. This is also referred to as a substitution.
Insertion: One or more nucleotide base pairs are introduced into a DNA sequence.
Deletion: One or more nucleotide base pairs are removed from a DNA sequence.
Inversion: A segment of DNA breaks and is inserted back into its original position in the reverse orientation.
Duplication: DNA is copied twice. The duplication can be part of a gene, a whole gene, or an entire genome

Question 16

Four key aspects of mutation that we need to keep in mind.

Answer 16

1st. Mutations can occur in the genomes of any cell, but for mutations to alter allele frequencies within a population, the mutation must occur in the DNA of cells that go on to produce gametes (e.g., sperm and egg).
2nd. Mutations are random and spontaneous events. This means that the precise location within the genome that they occur in and when they occur cannot be predicted.
3rd. Mutations are not directed to occur at specific genes because of the selective pressures on a population. For example, mutations within a bacterial population exposed to higher than normal temperatures will not be localized to the genes of heat-sensitive enzymes resulting in the enzymes being better able to function at high temperatures.
4th. Mutation does not tend to result in increased fitness. In fact, most mutations either have no effect on fitness (neutral) or they will be harmful (deleterious) to an organism.

Question 17

The importance of mutation to evolution

Answer 17

Is not that it allows for rapid change to a population; it doesn’t. In fact, genetic drift, gene flow, and natural selection can all change allele frequencies faster. Rather, the value of mutation is that it is the only microevolutionary process that gives rise to genetic novelty.

Natural selection is usually the most powerful mechanism driving evolutionary change, but selection is only choosing among alleles that already exist in the population. Natural selection does not create, for example, new proteins that have new advantageous functions. These come about when mutation causes DNA sequences to change to new gene sequences that give rise to new functions never seen before. If such a novelty is beneficial, the allele will become more common within the population through natural selection.

Question 18

Directional selection

Answer 18

A type of selection in which individuals near one end of the phenotypic spectrum have the highest relative fitness. After selection, the trait’s mean value is higher or lower than before, and variability in the trait may be reduced. Is extremely common. For example, predatory fish promote directional selection for larger body size in guppies when they selectively feed on the smallest individuals in a guppy population.

Question 19

Stablizing selection

Answer 19

A type of natural selection in which individuals expressing intermediate phenotypes have the highest relative fitness. Probably the most common mode of natural selection. For example, very small and very large human newborns are less likely to survive than those born at an intermediate weight

Question 20

Disruptive selection

Answer 20

A type of natural selection in which extreme phenotypes have higher relative fitness than intermediate phenotypes. Is much less common than directional selection and stabilizing selection.

Question 21

Agents of Microevolutionary Change table

Answer 21

Gene Flow-
Agent Definition: Change in allele frequencies as individuals join a population and reproduce

Effect on Genetic Variation: May introduce genetic variation from another population

Effect on Average Fitness: Unpredictable effect on fitness; may introduce beneficial or harmful alleles

Genetic Drift-
Agent Definition: Random changes in allele frequencies caused by chance events

Effect on Genetic Variation: Reduces genetic variation, especially in small populations; can eliminate rare alleles

Effect on Average Fitness: Unpredictable effect on fitness; often harmful because of lost genetic diversity

Natural selection-
Agent Definition: Differential survivorship or reproduction of individuals with different genotypes One allele can replace another or allelic variation can be preserved.

Effect on Genetic Variation: Positive effect on fitness through evolution of adaptations Mutation Heritable change in DNA Introduces new genetic variation into population; does not change allele frequencies quickly.

Effect on Average Fitness: Unpredictable effect on fitness; most mutations in protein-coding genes lower fitness

Question 22

inbreeding

Answer 22

A special form of nonrandom mating in which genetically related individuals mate with each other. Particular issue in small populations, but is a reproductive strategy that is found in many plant species and invertebrate animals.

Does not cause evolution because the allele frequencies do not change over time. Inbreeding doesn’t change the proportion of alleles in a population, it simply moves them from heterozygous into both homozygous genotypes.

Question 23

Inbreeding depression

Answer 23

A decline in the average fitness of inbred individuals in a population. The explanation for this is that deleterious alleles (e.g., they may code for a non-functioning protein) tend to be recessive, and yet they perpetuate in a typical population because they are carried in heterozygotes where they are effectively masked. However, as a result of inbreeding, there is an increased proportion of homozygous recessive genotypes at any particular locus that are usually harmful and even lethal to individuals that carry them.

The solution to inbreeding depression is simple: outbreeding; that is, introduce individuals from other populations, which invariably come with new alleles.

Question 24

Sexual selection

Answer 24

A form of natural selection established by male competition for access to females and by the females’ choice of mates. Males of a species who often possess a range of ornaments, such as brightly coloured feathers, long tails, or impressive antlers and horns, that often form part of elaborate courtship behaviour.

Sexual selection encompasses two related processes.
As the result of intersexual selection (i.e., selection based on the interactions between males and females), males produce these otherwise useless ornaments simply because females associate them with health and vigour. In many species, intersexual selection is the likely cause of sexual dimorphism—differences in the size or appearance of males and females.
Under intrasexual selection (i.e., selection based on the interactions between members of the same sex), males use their large body size, antlers, or tusks to intimidate, injure, or kill rival males.

Like directional selection, sexual selection pushes phenotypes toward one extreme.

Question 25

sexual asymmetry.

Answer 25

Because eggs are more energetically expensive to make than sperm and are limited in number, females are much more heavily invested in successful reproduction than males.

Female fitness is closely linked to producing eggs and rearing healthy offspring (e.g., pregnancy, lactation).

In contrast, because sperm are energetically very cheap to produce, males can father a huge number of offspring. Male fitness then is limited simply by the number of females an individual male can mate with.

This sexual asymmetry means that females need to be far more discriminating than males about who they mate with. They have a limited number of energetically expensive eggs, and identifying a mate that is particularly healthy is important.

Question 26

Diploidy and haploid

Answer 26

diploidy is a valuable mechanism that maintains genetic variability in a population. Although recessive alleles may be harmful, this is only the case when both alleles for a particular gene are recessive. An important aspect of diploidy is that the maintenance of recessive alleles may have important ecological considerations. Recessive alleles represent genetic diversity and, while under present conditions they may be harmful and lower fitness in the homozygous recessive state, they may prove beneficial to a population if the environmental conditions change.

Question 27

Balancing selection

Answer 27

A type of natural selection in which more than one allele is actively maintained in a population. Natural selection preserves balanced selection when (1) heterozygotes have higher relative fitness, (2) when different alleles are favoured in different environments, and (3) when the rarity of a phenotype provides a selective advantage.

Question 28

Heterozygous advantage

Answer 28

An evolutionary circumstance in which individuals that are heterozygous at a particular locus have higher relative fitness than either homozygote.

Question 29

Selection in Different Environments

Answer 29

Genetic variability can also be maintained within a population when different alleles are favoured in different places or at different times.

Question 30

Frequency-Dependent Selection

Answer 30

• When fitness is dependent upon the frequency of a phenotype or genotype in a population.
• In frequency dependent selection, phenotypes that are either common or rare are favoured through natural selection.

• Negative: selects for rare phenotypes in a population increases a populations genetic variance. Only one that favours variances.

-Positive: selects for common phenotypes in a population and decrease genetic variances.

Sometimes, genetic variability is maintained in a population simply because rare phenotypes—whatever they happen to be—have higher relative fitness than more common phenotypes. The rare phenotype will increase in frequency until it becomes so common that it loses its advantage. Such phenomena are examples of frequency-dependent selection because the selective advantage enjoyed by a particular phenotype depends on its frequency in the population.

Question 31

Polymorphism

Answer 31

Is the occurrence of two or more clearly different morphs or forms in species.

•To be classified as a morph, must occupy the same habitat at the same time and belong to her panmictic population

Question 32

Phenotype

Answer 32

An attribute of an organism, such as it’s behavior, morphology, or physiology.

Question 33

Genotype

Answer 33

The set of genes an organism carries.

Question 34

Genotype frequency

Answer 34

Percentages of individuals possessing that genotype.

Question 35

Allele frequency

Answer 35

Calculated from genotype and deployed organisms

• p and q: 2 different alleles at a locus

Question 36

Hardy-Weinberg principle formulas

Answer 36

Frequency of Genotype:
p^2 + 2pq + q^2 = 1

Frequency of allele:
p + q = 1

p = Frequency of the dominant allele in a population.

q = Frequency of the recessive allele in a population.

Question 37

Adaptive radiation

Answer 37

In evolution or biology, it’s a process in which organisms diversify rapidly from an ancestry species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches.