Ch. 13 How Populations Evolve
The recessive allele of a gene causes cystic fibrosis. For this gene among Caucasians, p = 0.98. If a Caucasian population is in Hardy-Weinberg equilibrium with respect to this gene, what proportion of babies is born homozygous recessive and therefore suffers cystic fibrosis?
(0.02)^2 = 0.0004
Suppose that, with regard to a particular gene with two alleles, A and a, we know that 60% of the alleles in the gene pool of a particular large population are A. We observe this population for five generations, during which we know that no mutation, selection, or migration has occurred. After this period, the frequency of the a allele is expected to be _____.
0.4 (If 60% of the alleles are A, p = 0.6. Because q = 1 - p, the frequency of the a allele must be 0.4. The conditions are compatible with equilibrium, so those frequencies should be maintained.)
Suppose there is a population of 100 rabbits. In this population, 60 rabbits are FF, 20 are Ff, and 20 are ff.
0.7 (There are 100 rabbits in the population, each with two alleles for the fur color gene, for a total of 200 alleles in the gene pool. Since there are 60 FF rabbits, there are 60 × 2 = 120 F alleles from these rabbits. Since there are 20 Ff rabbits, there are 20 ×1 = 20 F alleles from these rabbits. This gives a total of 120 + 20 = 140 F alleles in the gene pool. Since the gene pool has 200 total alleles, the allele frequency for the F allele is 140 / 200 = 0.7.)
In human gamete production there is an average of _____ crossover events per chromosome pair.
2-3
In artificial selection, humans provide the selective pressure for species to change and shape the evolution of various breeds. What provides the selective pressure in natural selection?
the environment
If color is an inherited trait in beetles, and birds are more likely to eat brown beetles than green beetles,
the frequency of the green allele will increase.
In a large population of randomly breeding individuals, the frequency of a recessive allele is initially 0.3. There is no migration. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.
the frequency of the individuals who express the dominant phenotype will go down, and the frequency of homozygous recessive individuals will go up (The frequency of individuals who express the dominant phenotype should decline, and the proportion of individuals who express the recessive phenotype (homozygous recessives) should increase.)
Genetic drift is a process based on _____.
the role of chance
A mutation occurs when _____.
there is a change in the DNA sequence of a gene
All of life is related through common ancestry, accounting for the _____________ of life.
unity
Mutation
A change in the nucleotide sequence of DNA
Population
A group of individuals of the same species living in the same area that interact with each other.
How are adaptations beneficial to organisms?
Adaptations help organisms survive and reproduce in a particular environment.
Suppose that every few years, all people over 6 feet tall do not have any children. How will this affect the human population?
Alleles that promote "tallness" will decrease in frequency.
Allele
An alternative version of a gene.
Which of the following statements best describes how the process of natural selection works?
Better-adapted individuals will leave behind more offspring to pass on their alleles, producing a dynamic "fit" between a population and its changing environment.
Microevolution
Changes in allele frequencies in a population over time
TRUE OF FALSE (CHARLES DARWIN): He based his theory on the inheritance of acquired characteristics.
False
TRUE OF FALSE (CHARLES DARWIN): He was the first to discover that living things can change, or evolve.
False
TRUE OF FALSE (CHARLES DARWIN): He worked out the principles of population genetics.
False
TRUE OR FALSE (AMOEBA POPULATION): It is healthier than the starting population.
False
TRUE OR FALSE (AMOEBA POPULATION): It is less vulnerable to extinction because it survived the catastrophe.
False
TRUE OR FALSE (NATURAL SELECTION): Natural selection starts with the creation of new alleles that are directed toward improving an organism's fitness.
False
TRUE OR FALSE (THIS IS AN EXAMPLE OF NATURAL SELECTION): A storm kills more green beetles than brown beetles by chance.
False
TRUE OR FALSE (THIS IS AN EXAMPLE OF NATURAL SELECTION): Green beetles and brown beetles always leave the same number of offspring.
False
TRUE OR FALSE (THIS IS AN EXAMPLE OF NATURAL SELECTION): Green beetles migrate out of the population, and brown beetles migrate into the population.
False
TRUE OR FALSE (THIS IS AN EXAMPLE OF NATURAL SELECTION): Green beetles migrate out of the population.
False
TRUE OR FALSE: An organism buried in fine sediments at the bottom of a lake would be prevented from becoming part of the fossil record when it dies
False
TRUE OR FALSE: An organism frozen in ice would be prevented from becoming part of the fossil record when it dies
False
TRUE OR FALSE: An organism trapped in sap would be prevented from becoming part of the fossil record when it dies
False
TRUE OR FALSE: If a population is in Hardy-Weinberg equilibrium and remains in equilibrium, the dominant allele will take over.
False
TRUE OR FALSE: If a population is in Hardy-Weinberg equilibrium and remains in equilibrium, the population organisms will evolve.
False
TRUE OR FALSE: If a population is in Hardy-Weinberg equilibrium and remains in equilibrium, the relative frequencies of three genotypes (AA, Aa, aa) will gradually become stabilized at 1:1:1. Submit
False
TRUE OR FALSE: In the example described in the tutorial, the red amoebas survived the catastrophic event, and all future generations of amoebas were red because the red amoebas had a higher reproductive rate than the blue ones.
False
TRUE OR FALSE: Increased population size could be caused by a population bottleneck.
False
Color is an inherited trait in beetles. If brown beetles move into a population from a nearby island, which of the following statements is correct?
Gene flow causes the frequency of the brown allele to increase.
Microevolution
Generation-to-generation change in the allele frequencies in a population
The bottleneck effect
Genetic drift resulting from a disaster that drastically reduces population size
What is a possible weakness of the fossil record?
Many species probably did not die in the right place at the right time to be captured in fossils, and many fossils will never by found by paleontologists.
Which condition would disturb the Hardy-Weinberg equilibrium and cause the gene pool to change?
Several homozygous recessive individuals leave the population.
What was significant to Darwin about the fauna and flora of the Galápagos Islands?
The species were similar to South American species, indicating common descent, but they had been extensively modified and were well-adapted to island life.
Gene pool
The total collection of alleles in a population at a given time
Mutation
The ultimate source of all new alleles
TRUE OF FALSE (CHARLES DARWIN): He proposed natural selection as the mechanism of evolution.
True
TRUE OR FALSE (AMOEBA POPULATION): It is more vulnerable to extinction due to lack of genetic variation.
True
TRUE OR FALSE (NATURAL SELECTION): Natural selection and evolutionary change can occur in a short period of time (a few generations).
True
TRUE OR FALSE (NATURAL SELECTION): Natural selection can be observed working in organisms alive today.
True
TRUE OR FALSE (NATURAL SELECTION): Natural selection depends on the local environment at the current time.
True
TRUE OR FALSE (THIS IS AN EXAMPLE OF NATURAL SELECTION): Green beetles leave more offspring than brown beetles because they are better at finding food.
True
TRUE OR FALSE: An organism fully decomposed by bacteria and fungi would be prevented from becoming part of the fossil record when it dies
True
TRUE OR FALSE: Changes in allele frequency could be caused by a population bottleneck.
True
TRUE OR FALSE: If a population is in Hardy-Weinberg equilibrium and remains in equilibrium, individuals survive and reproduce equally well regardless of their genotype.
True
TRUE OR FALSE: Loss of alleles could be caused by a population bottleneck.
True
TRUE OR FALSE: Reduction in genetic variability could be caused by a population bottleneck.
True
Natural selection
Will tend to produce adaptive changes in populations
What is the best example of gene flow?
Wind blows pollen from one population of plants to another, and cross-fertilization occurs.
As in the previous question, suppose there is a population of 100 rabbits that have different fur patterns. *In this population several generations ago, there were 60 FF rabbits, 20 Ff rabbits, and 20 ff rabbits. *Over time, the population changed, and now there are 40 FF rabbits, 40 Ff rabbits, and 20 ff rabbits. Has microevolution occurred? Why or why not?
Yes, because the allele frequencies have changed.
Which person has the highest evolutionary fitness? 1) a man who lives to be 68 and has 7 children and 15 grandchildren 2) a woman who lives for 105 years and has no children 3) a woman who lives to be 78, has 10 children, but no grandchildren 4) a man who can run a marathon in less than 3 hours
a man who lives to be 68 and has 7 children and 15 grandchildren
This unequal reproduction in a population leads to the gradual accumulation of _____________ to the environment.
adaptations
Broccoli, cabbages, and Brussels sprouts all descend from the same wild mustard and can still interbreed. These varieties were produced by
artificial selection
In natural selection, _____ determine which phenotypes are successful.
current conditions in the local environment
The _____________ of life arises from the adaptation of species to different habitats over long spans of time.
diversity
The Illinois populations of the greater prairie chicken benefited when managers brought in prairie chickens from other populations. This restored genetic variation to the Illinois populations through the process of __________.
gene flow
The ease with which humans travel across the globe is likely to increase _____.
gene flow
All the genes in a population are that population's _____.
gene pool
Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.
genetic drift
In populations of the greater prairie chicken in Illinois, genetic diversity was lost through
genetic drift and restored by gene flow.
The evolution of populations due to chance is
genetic drift.
In a population with brown and green alleles for color, genetic drift
has more effect on the evolution of a small population.
Two key observations underlying natural selection are that members of a population vary in their _____________ and that all species can produce more offspring than the environment can support.
inherited traits
Homologous pairs of chromosomes are lined up independently of other such pairs during _____.
metaphase I
The phrase Darwin used to describe his broad theory of evolution is ''descent with _____________.''
modification
Genetic drift is __________.
more likely to have an impact on small populations
Darwin proposed a mechanism for how evolution occurs, which he called _____________.
natural selection
Crossing over, resulting in an increase in genetic variation, occurs between _____.
nonsister chromatids of homologous chromosomes
Darwin inferred that those organisms with traits best suited to the environment tend to leave more _____________ than other members of a population.
offspring
Imagine that you are studying a very large population of moths that is isolated from gene flow. A single gene controls wing color. Half of the moths have white-spotted wings (genotype WW or Ww), and half of the moths have plain brown wings (ww). There are no new mutations, individuals mate randomly, and there is no natural selection on wing color. How will p, the frequency of the dominant allele, change over time?
p will neither increase nor decrease; it will remain more or less constant under the conditions described.
The frequency of homozygous dominant individuals in a population that is in Hardy-Weinberg equilibrium is equal to
p^2
What is the concept of natural selection?
reproductive success influenced by inherited characteristics
Darwin found that many of the species on the Galápagos Islands
resembled species on the nearest mainland.
Why was Darwin's acceptance of an ancient, continuously changing Earth so important in his development of his ideas about evolution?
Darwin hypothesized that species changed gradually, over long spans of time, in response to diverse and changing habitats.
Each of us is part of the ongoing evolution of the human species. Which of the following forms of microevolution is currently most important in human populations worldwide?
Global travel and migration are promoting gene flow on an unprecedented scale.
Which of the following statements best describes the true nature of natural selection?
Heritable traits that promote reproduction become more frequent in a population from one generation to the next.
The forelimbs of humans, cats, and bats have a number of detailed similarities in their construction. What best explains these similarities?
The forelimbs are similar because all of these organisms inherited the basic forelimb design from a common ancestor.