Chapter 15
Which of the following examples is the best analogy to the imperfection of natural selection at producing organisms perfect for their environments?
A baker being asked to make a 3-tiered, lemon cake with ingredients on-hand in the kitchen
Why is it beneficial, in populations that reside at extreme altitudes, for individuals to produce less hemoglobin, even though there is less oxygen in the air?
Because individuals who produce less hemoglobin do not run the risk of chronic mountain sickness.
Classify the following examples based on the type of natural selection they describe.
Directional selection - Chloriquine is no longer effective against malaria because it has evolved resistance against it ; A new flu vaccine is created every year Disruptive selection - One population of finches occupy different niches and eventually evolve to have different beak sizes; British land snails compromise two very different phenotypes as they are both adapted to different habitats Stabalizing selection- Very large and very small newborns are more likelynto suffer serious health problems; Bird clutch sizes consisting of 4-5 eggs are more likely to hatch than larger or smaller clutches
A population of peppered moths is monitored over several generations. It is observed that the number of white moths compared to the number of black moths changes with each successive generation. This means that the population cannot be at equilibrium and the population is therefore evolving.
False
True or false: Nonrandom mating is required to meet the assumption of the Hardy-Weinberg principle.
False
Two populations of plants that live near one another have very similar allele frequencies. What could be a logical conclusion regarding gene flow between these populations?
Gene flow is frequent.
If mutations, nonrandom mating, natural selection, gene flow, or genetic drift occur in a population, ______ will not remain in effect, and evolutionary change will occur.
Hardy-Weinberg equilibrium
Complete the following statements to describe heterozygote advantages. Not all choices will be used more than once.
Individuals with sickle-cell disease have a(n) HOMOZYGOUS RECESSIVE genotype and tend to die at an early age due to hemorrhaging and organ destruction. Individuals that are HETEROZYGOUS and have the sickle-cell trait are better off because their red blood cells usually become sickle-shaped only when the oxygen content of the environment is low. Individuals that carry an allele for the sickle-cell trait also carry a(n) RESISTANCE to malaria because the sickle-shaped RED BLOOD CELLS lose potassium and thus cannot support the malarial parasites. Therefore, individuals that are HETEROZYGOUS. carry an advantage, as they are resistant to malaria and do not have sickle-cell disease.
Complete the following statements to describe the effect of mutations on a population. Choices may be used more than once or not at all.
Mutations are permanent changes made to an organism's DNA. Mutations can be HARMFUL, neutral or beneficial depending on the ENVIRONMENT of the organisms. The rate of the mutations is very LOW, but they provide the raw material for EVOLUTION to occur as they provide new VARIATIONS among offspring. For example, most Daphnia survive best at temperature around 20 DEGREES ; however a mutation exists that require Daphnia to live in temperatures between 25 and 30 DEGREES. For Daphnia in colder climates, this mutation could be HARMFUL, but for Daphnia in warmer climates, this mutation could be neutral or even BENEFICIAL.
Can sexual reproduction alone cause a change in allele and genotype frequencies in a population?
No
Complete the following statements to describe how heterozygotes maintain variation in populations. Choices may be used more than once.
One of the tenets of NATURAL SELECTION is that within populations,VARIATION exists amongst the individuals. The VARIATION is generated through MUTATIONS, recombination, independent assortment, and gene flow. Because only alleles that are phenotypically expressed are subject to the pressures of NATURAL SELECTION, heterozygotes can be protectors of RECESSIVE alleles that could possibly be lost otherwise. As long as the heterozygote survives, so do RECESSIVE alleles and their corresponding PHENOTYPES, which could possibly have greater fitness in a changing environment. When natural selection favors the ration of two or more PHENOTYPES over multiple generations, it is called balanced polymorphism.
In cases of major or minor altitude changes, there is an observable increase in hemoglobin, the component of the blood that carries
Oxygen
Test your understanding of micro evolution by completing each statement. Not all choices will be used and some will be used more than once.
Peppered moths can be light or dark in color, and this coloration is controlled by a single set of ALLELES. The dominant allele encodes for MELANIN production, which creates dark coloration in the moths. Im the other hand, individuals with two recessive alleles will show LIGHT phenotypes. Previous to the rise on industry in Britain, the frequency of the LIGHT phenotype was predominant and enhanced the survival of moths. With the advent of industry, however POLLUTION the darkened the tree trunks, resulting in an increased frequency of the dark phenotype. This illustrates the process of MICROEVOLUTION and shows that natural selection can occur even over a short period of time.
Complete the following statements about Hardy-Weinberg equilibrium. Not all choice will be used and some will be used more than once.
The Hardy-Weinberg equation is used to calculate the GENOTYPE and allele frequencies of a population. According to this equation, the term p2 represents the HOMOZYGOUS DOMINANT individuals within a population. Secondly, the term q2 represents the HOMOZYGOUS RECESSIVE individuals within a population. Finally, the term 2pq represents the HETEROZYGOUS individuals within a populations. The relationship between the components of the Hardy-Weinburg equation will remain constant throughout GENERATIONS, providing five conditions are met. Mutations cannot occur. Gene flow cannot allow alleles into or out of the population. Individuals must pair RANDOMLY. Genetic drift does not occur. All genotypes have an EQUAL chance to survive.
If a population does not meet the requirements of the Hardy-Weinberg equilibrium, how would the allelic frequencies of that population be affected?
The allele frequencies may increase or decrease
Evaluate your understanding of the process of gene flow by completing each statement. Not all choices will be used.
The movement of alleles among adjacent populations via migration of breeding organisms is called GENE FLOW. Gene flow INCREASES variations within a population by introducing new alleles from another separate population. However continued gene flow due to migration of individuals actually DECREASES allele frequency differences because it make the GENE POOLS similar in these adjacent populations. Over time, this can prevent SPECIATION from occurring in these areas. Instead SUBSPECIES are created that do possess some unique characteristics but are still capable of interbreeding with each other.
During directional selection, which direction will the distribution curve shift towards?
The right side of the distribution
In a population of peppered moths, the allele frequency of d shifts from 0.49 to 0.64 over succession generations. That means this population is not at equilibrium and is therefore evolving.
True
True or false: Individuals who are members of different subspecies within the same species can interbreed.
True
Which of the following represents the genotypic frequency of a population?
aa = 24%
Populations acquire adaptations through natural selection to biotic and __ components in their environment.
abiotic
Population genetics studies the __ available in the gene pool of the population.
alleles
The type of mating occurs when individuals tend to mate with those that have the same phenotype, with respect to a certain characteristic, is referred to as ___ mating.
assortative
Changes in the allele and genotype frequencies __ be caused by sexual reproduction alone.
cannot
Which type of selection is evident if an extreme phenotype is favored and the distribution curve shifts towards that extreme phenotype?
directional selection
Genotypic variation in a population may provide a species with options when the __ changes.
environment
Introduction of new or rare alleles into a population through the migration of individuals from another population is called gene
flow
Movement of alleles among populations by migration of breeding individuals is termed __.
gene flow
The movement of alleles from one population to another is referred to as
gene flow
The various alleles at all the gene loci in all individuals in a population is called the
gene pool
A small amount of gene flow between populations can _____ the variation within a population while a continuous gene flow can _____ the difference in allele frequency between the populations.
increase, decrease
Small measurable evolutionary changes within a population from generation to generation refer to a type of evolution called .
microevolution
The increase in allele frequency for dark fur in a population of foxes is an example of __.
microevolution
A permanent genetic change that may produce phenotypic variation within a populations is called a genetic
mutation
A(n) __ occurs when DNA is damaged or changed in such a way as to alter the genetic message carried by its genes.
mutation
The process that results in adaptation of a population to the biotic and abiotic environments is __ selection.
natural
Adaptations to the environment are not often perfect because natural selection
only directs the modification of features already present
Which of the following is the correct binomial expression for the Hardy-Weinberg principle?
p2 + 2pq + q2 = 1
Match each of the following components of the expressions for Hardy-Weinberg equilibrium with its correct description.
p2 > frequency of the homozygous dominant genotype in the population 2pq > frequency of the heterozygote genotype in the population q2 > frequency or the homozygous recessive genotype in the population
If natural selection favors the ratio of two or more phenotypes generation after generation, it is called balanced ______.
polymorphism
When two or more phenotypes remain in a population generation after generation, a type of equilibrium called a balanced __ exists.
polymorphism
The field of study in which the principles of genetics are applied to populations is known as
population genetics
Which of the following is not one of the conditions that causes evolutionary change?
random mating
Which of the following is not required in order to maintain the Hardy-Weinberg equilibrium?
selective mating
Adaptive changes in males and females that lead to an increased ability to secure a mate are termed __ selection.
sexual
When males or females display characteristics that make them more attractive to the opposite sex, __ selection results.
sexual
An intermediate phenotype is favored by __ selection.
stabilizing
The type of selection that occurs when an intermediate phenotype is favored is called __ selection.
stabilizing
Having genotypic __ in a population may provide a species with options for survival if the environment changes.
variation
