Download Biology 182: Study Guide

Biology 182: Study Guide
Purpose: This study guide provides a checklist of terms, concepts and topics covered in Bio182.
Although arranged by chapters from your text, topics may be presented at various times in lecture
and lab. This guide is not exhaustive. Use this guide with your lecture & lab notes, along with your
text, handouts and MasteringBiology to create your own set of working notes. This guide may help
you identify concepts that need further clarification. For additional review answer the questions at
the end of each chapter in your text. NOTE: Your knowledge of BIO181 is expected for this
course. Review Chapter 1’s themes, evolution, and the scientific method.
PART I. MECHANISMS OF EVOLUTION: Chapters 22-26
Chapter 22. Descent with Modification: A Darwinian View of Life
This chapter introduces the Theory of Evolution by Natural Selection, from the philosophical roots
of western culture to the presentation of Darwin’s book, ‘The Origin of Species’. The end of the
chapter includes recent evidence that further supports evolutionary theory and evolution as fact.
You should be able to identify some of the most important researchers in this field, and their
contributions to our understanding of evolution. Below is a list of names and terms:
Plato: idealism / essentialism
natural theology
Aristotle: scala naturae (scale of nature)
Linnaeus: taxonomy
Cuvier: catastrophism
Hudson: gradualism
Malthus: struggle for existence
Lyell: uniformitarianism
Lamarck: evolution by acquired characteristics
Darwin: evolution by natural selection
Wallace: independently hypothesized evolution by natural selection
Be able to explain how fossil evidence (e.g. from Cuvier & Lamarck) and new theories in geology
(e.g. from Hudson & Lyell) set the stage for Darwin’s theory.
The Voyage of the Beagle included surveys of South America and the Galapagos Islands. Be able to
describe observations made at both locations and how they influenced Darwin. For example, why
were organisms from temperate areas of South America more like organisms from tropical South
America than like organisms from Britain (a temperate climate)?
Be able to describe the observations and inferences that make up the theory of natural selection as
summarized by Ernst Mayr (see page 8 of this study guide) and simplified in your text (p. 469);
compare to the changes in your ‘lizards’ from lab (first week).
According to Darwin’s theory, what is the smallest unit of life that can evolve? Explain.
What is artificial selection? How did it influence Darwin?
Be able to discuss the difference between evolution as a fact (e.g. soapberry bugs, MRSA, guppies)
and the Theory of Evolution by Natural Selection.
How do scientists define ‘theory’?
Be able to describe examples from the following disciplines that suggest evolution has occurred:
biogeography
comparative embryology
fossils/paleontology
molecular biology
comparative anatomy
design ‘flaws’
Also know:
homology(-ous)
vestigial organ
analogy(-ous)
homoplasy
convergent evolution
phylogeny
Be able to define an adaptation as: 1) a new feature, 2) shaped by natural selection, 3) that provides
a performance benefit.
Chapter 23. The Evolution of Populations (Microevolution)
This chapter focuses on microevolution with use of the Hardy-Weinberg Equilibrium (HWE). The
chapter opens with a look at genetic variation within populations. It closes with discussions of how
genetic variability is preserved, and the limits of natural selection.
Be able to answer these questions. What is the source of genetic variation? How much genetic
variation exists in natural populations? How is this variation maintained? How important is genetic
variation to evolution by natural selection? to other mechanisms of evolution?
You should be able to explain why early evolutionary biologists were at conflict with geneticists,
and how that conflict was resolved (the modern synthesis, presented in lecture). Also, be able to
define population genetics: the study of how populations change genetically over time.
Microevolution is the generation-to-generation change in a population’s genetic structure, the
smallest level of evolution. The HWE provides a model for understanding microevolution. Be able
to name the five assumptions of this model and their counterparts, the five mechanisms of
evolution, with examples of each mechanism. Which of these mechanisms is/are expected to adapt a
population to its environment?
Assumptions of HWE
Type of Microevolution
1. Very large (infinite) population.
1. Genetic drift (bottleneck, founder effect)
2. Isolation from other populations (no gene flow) 2. Gene flow (migration)
3. No net mutations
3. Mutation
4. Random mating (panmictic population)
4. Assortative mating
5. No natural selection
5. Natural selection
Understand and be able to use the formulas of the HWE to determine the current allelic and
genotypic frequencies of a population, and from these data the expected allelic and genotypic
frequencies of subsequent generations.
Sample HWE question: (find more HWE problems at the end of this study guide)
Show mathematically and describe in evolutionary terms, why the HWE predicts that a parental
population of infinite size with: p = 0.6 and q = 0.4 should give rise to offspring with these
genotypic frequencies: AA = 0.36, Aa = 0.48, aa = 0.16
Be able to define, describe and use the following terms:
population
gene pool
founder effect
gene flow
polymorphism
cline
frequency-dependent selection
genetic drift
inbreeding
hybrid vigor
fitness
bottleneck effect
assortative mating
balanced polymorphism
What is the neutral theory? (pp 482-483, see also p 561) Why is it hard to test this theory?
What does natural selection act on or ‘see’: phenotype or genotype? Explain.
Be able to describe the three modes of natural selection: stabilizing selection, directional selection
and diversifying (disruptive) selection, and draw a graph typical of each mode.
What are the costs and benefits of sexual reproduction?
What is anisogamy theory and how does it relate to sexual selection?
What is sexual selection? How does it differ from natural selection? How and why do the sexes
differ in their approach to mate choice? How does sexual selection relate to nonrandom mating?
What is group selection? How important is it relative to selection on individuals?
Can evolution perfect organisms? Explain.
Do imperfections in organisms support or refute the theory of evolution by natural selection?
Chapter 24. The Origin of Species
This chapter addresses the ‘species question’: What is a species and how do new species arise?
Scientists have provided a variety of answers to both of these questions. Moreover, most of these
explanations are not exclusive. This subject matter provides some of the best examples of how
difficult it is to pigeon-hole life. You should focus on the different species concepts and how they
address the questions above (what is a species? how do they arise?) the problems with each concept,
and how they overlap. Importantly, the Biological Species Concept (BSC), developed by Ernst
Mayr (1942) was central to the Modern Synthesis. It emphasized the mechanisms that keep species
separated (reproductive isolating mechanisms) and by inference, mechanisms of speciation.
Prior to the modern synthesis, most people grouped organisms into species based on their similar
appearance: shape (morphology), color, number of bones, fins, etc. the Morphological Species
Concept. This method works for people from diverse cultures.
For example, Ernst Mayr identified and named 137 species of birds in the Arafak Mountains of
New Guinea. The native people of these mountains had named 138 types of bird. This method of
naming species (the Morphological Species Concept) is similar to that of Linnaeus. How common
was this method used in the naming of species in the past? What other species concepts are similar
to this concept?
Ernst Mayr later proposed the Biological Species Concept. How does it differ from the
Morphological Species Concept? What kinds of scientists can use the BSC? Who cannot? The key
features to the BSC is the notion that individuals of a species can only breed with conspecifics
(other members of the same species) to produce viable, fertile offspring. Conversely, they do not
mate with members of other species to produce viable, fertile offspring.
Note the importance of the BSC to the Modern Synthesis – the joining of evolution by natural
selection and Mendelian genetics. Members of populations exchange their genetic material and
pass them on to new generations. If populations no longer exchange alleles, they may gradually
change separately from each other to the point at which they can no longer interbreed, i.e. new
species can evolve! For example, if two populations become separated by a river or mountain chain,
Allopatric Speciation may occur.
Mayr and his followers spent much energy to compile a list of reproductive isolating mechanisms.
Be able to describe each and identify examples from your text/lecture.
Prezygotic (before fertilaztion) Barriers:
Habitat Isolation
Temporal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
Postzygotic Barriers:
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Many other species ‘concepts’ (definitions) exist: The Recognition Species Concept differs from
the BSC in the mechanism(s) that select for mating between conspecifics. While the BSC
emphasizes reproductive isolating mechanisms (selection against mating with other species), the
Recognition Species Concept proposes a Specific Mate Recognition System. Selection acts on
mate choice so that individuals choose the best possible mate, which will necessarily be a
conspecific. Which of these concepts is most consistent with the process of natural selection? How
does this relate to Sexual Selection?
Your text mentions other Species Concepts. The Phylogenetic (Evolutionary/Genealogical)
Species Concept defines a group by its unique phylogeny and practically by its set of genes. This
concept is often applied to populations of wildlife (e.g. salmon) as Evolutionarily Significant
Units (ESUs) for the purpose of conservation. The Ecological Species Concept separates related
forms based on their different ecological roles or niches. Several other types of species concepts
have been proposed, such as the Nominal Species Concept that suggests ‘species’ are simply
convenient ‘names’ humans use to group organisms. Be able to compare and contrast these species
concepts. Which of these species concepts focus on the process of speciation and which focus on
the diagnosis of a species?
Although Species Concepts have generated much controversy, they are necessary to define the
origin of new species. The processes of speciation and their relative importance to the history of life
on Earth are even more contentious. Speciation may occur under two general geographic scenarios:
Allopatric (other country) Speciation and Sympatric (same country) Speciation. Note that these
scenarios were an integral part of the BSC when proposed by Mayr. You should be able to discuss
each in terms of the reproductive isolating mechanisms that might lead to separate species. Which
scenario did Mayr think more commonly led to speciation events?
The classic Allopatric Speciation model describes a large population that becomes separated by a
geographical barrier, such that two (still relatively) large populations are created. Over time, the two
populations will diverge as they follow their own evolutionary trajectories. Your text also refers to
‘small, isolated populations’ as more likely to diverge. These are also known as peripheral
isolates and this hypothesis is also known as Peripatric Speciation - a distinct variation of the
classic Allopatric model.
Be able to define and describe Allopatric, Peripatric, and Sympatric speciation. Which of these is
considered to be the most common for animals? What special modes of sympatric speciation are
common to plants but not animals? How does reproductive isolation occur in each mode? What is
the role of islands on speciation and what is an adaptive radiation? Which form of speciation
occurs on islands? How is it different from other scenarios? (Note: We will see in the next section
that adaptive radiations also follow major extinction events).
Hybrid Zones provide important examples of incipient speciation. Be familiar with the examples in
your text and the three potential outcomes: reinforcement, fusion and stability. Similar examples
come from ring species. Several examples were provided in earlier editions of your text, such as
Peromyscus maniculatus (see attached page). Ring species consist of several distinct populations or
subspecies, with various amounts of contact and interbreeding between the subspecies. Ring
species represent living examples of speciation in process. If the other two subspecies went extinct,
would you consider P. m. artemisiae a separate species from P. m. nebrascensis? Apply each of the
species concepts in answering the question and explain why or why not. Are ring species consistent
with the theory of evolution? Explain.
Compare and contrast punctuated equilibrium vs. gradualism and the associated evidence.
The explosion of genetic studies provides much new information on both speciation rates and the
amount of genetic differentiation required for speciation (e.g. the Japanese snails, genus Euhadra,
sunflowers, monkey flowers: Mimulus spp, and Hawaiian Drosophila spp, pages 514-516). Be able
to use these examples.
What is Macroevolution? Can the processes of Microevolution explain the larger patterns of
evolutionary change?
Chapter 25. History of Life on Earth / Read Chapter 26 Before 25! (more details below)
We will study some parts of chapter 25 for our first exam, primarily those sections that focus on the
process of evolution, patterns and its study (e.g. fossils; sections 25.2, 25.4, 25.5 & 25.6). Major
events in biological history will be studied within our second section of the course (25.1 & 25.3).
Macroevolution is concerned with large-scale patterns in evolution: e.g. the origin of key
adaptations or novelties, mass extinctions, adaptive radiations, and increasing size in some taxa.
Chapter 24 introduced this term. Chapter 25 describes large-scale patterns of evolution and some of
the developmental changes that lead to novelties (e.g. heterochrony).
Be sure to read section 25.2 and be able to define fossil: the preserved remnants or impressions of
an organism that lived in the past (L. dug up) and the example of new groups (e.g.mammals).
What are the limitations of the fossil record? Be able to define or describe these terms:
sedimentary rock
radiometric dating
relative dating
half-life
superposition absolute dating
carbon-14
Be able to describe the evidence for plate tectonics (continental drift, 25.4), its explanatory value to
current biogeography, and its impact on the history of living things (e.g. the Permian extinction). Be
able to define and describe the following:
mass extinction
Mesozoic
adaptive radiations
Cenozoic
Pangaea
Precambrian
impact hypothesis
Paleozoic
Be able to compare and contrast global adaptive radiations and regional adaptive radiations.
How do these patterns compare to the causes of speciation discussed in Chapter 24?
Five mass extinction events were so dramatic as to be noted. A possible sixth extinction event may
be occurring. What is its cause?
Most evolutionary novelties (25.5 & 25.6) are modifications of existing structures. Recent studies
of regulatory genes have demonstrated that great changes in anatomy and morphology can be
created by rather simple changes in the rate and timing of development (heterochrony), and the
spatial pattern of expression produced by homeotic genes. The importance of development to the
origin of evolutionary novelties has led to the new term, evo-devo, that emphasizes this
relationship. Be able to define and present examples of the following:
allometric growth
adaptation
heterochrony
paedomorphosis
adaptive divergence
homeotic genes
Are species internally driven to change their shape or size? (refer to the evolution of horses)
Chapter 26. Phylogeny (Systematics) & The Tree of Life (will be covered in lab)
This chapter describes Systematics – the branch of modern biology that includes the Classification
of living things, from the initial two-Kingdom system of Linnaeus, to the modern groupings based
on evolutionary hypotheses. All of these methods place groups of organisms into nested sets.
Systematics consists of Taxonomy (naming) and Classification of taxa (singular taxon – a named
group of organisms). Be familiar with the binomial system of naming and the rest of the hierarchical
classification system: Domain (new term, includes Kingdoms) Kingdom, Phylum, Class, Order,
Family, Genus and specific epithet. The last two, Genus and specific epithet, make up the
scientific binomial – the ‘two-name’ descriptor unique for each species.
Modern schools of systematics include Phylogenetics and Cladistics. Importantly, these schools
share the goal of identifying the true evolutionary relationships between organisms. Because we
cannot observe the history of speciation events, we are limited to the generation of evolutionary
hypotheses indicating relatedness via common ancestry.
Various characters may be used to determine evolutionary relationships, as already mentioned: e.g.
morphology, anatomy, embryology, behavior and now molecules such as proteins, RNA & DNA.
Although Linnaeus created his system for ‘fixed species’ these same classifications are now
considered phylogenetic hypotheses – suggestions of the relationships between groups of
organisms. You should be able to describe the relationship between taxonomic hierarchies
(Phylum, Class, Order, etc.) and phylogenetic hypotheses.
Many modern systematists use cladistic analysis to create their phylogenetic hypotheses –
typically in the form of a tree or a cladogram (a clade = a monophyletic group, a specific type of
taxon). You should be able to use the methods of cladistics to create a cladogram or tree, and
understand the concepts associated with these trees (e.g. limitations).
To create a phylogenetic tree, it is important to distinguish between homologous vs. analogous
characters (aka homoplasies). Be able to define these terms and convergent evolution. We will
practice making trees in lab, but focus on visible characters. Read the sections on molecular
characters; they will be referenced, but briefly. You should also be able to define, describe and use the following terms: Monophyletic Paraphyletic Polyphyletic Clade Apomorphy Derived (new) character state Parsimony Synapomorphy Shared derived character state Outgroup Pleisiomorphy Ancestral character state Ingroup Orthologous genes Paralogous genes A phylogenetic hypothesis in the form of a tree carries much information including key adaptations
that define groups, relationships between groups, and some time scale (either absolute or relative).
You should be able to interpret this information from a tree.
Much of the remainder of our course focuses on the diversity of living organisms. The most
important aspects of each group will be presented in the form of trees. You must be able to
interpret trees to identify relationships and critical adaptations of these groups.
What is the molecular clock? What affects the reliability of this measure of relatedness? (recall
neutral evolution).
What is the importance of ‘intermediate forms’? How would you explain the evolution of a
complex character like a wing? For example, ‘What is the value of half a wing?’[Note: we will
address this question during this section, with additional examples from films.]
Darwin’s Theory of Evolution by Natural Selection * Observation 1. Populations have tremendous reproductive potential. Observation 2. Populations tend to be stable. Observation 3. Resources are limited. (Malthus 1798) Inference 1. Production of excess offspring leads to a struggle for existence; only a fraction of the offspring born will survive to reproduce. Observation 4. Individuals vary within a population. Observation 5. Much of this variation is heritable. Inference 2. Some variants will be better able to survive and reproduce in their environment. Inference 3. The reproductive differential between variants in the population will lead to a gradual change in the population, with favorable traits (adaptations) accumulating over the generations. * After Ernst Mayr. 1982
On the Origin of Species By Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life Charles Darwin, 1859* “From these considerations, I shall devote the first chapter of this Abstract to Variation under Domestication. We shall thus see that a large amount of hereditary modification is at least possible; and, what is equally or more important, we shall see how great is the power of man in accumulating by his Selection successive slight variations. I will then pass on to the variability of species in a state of nature; but I shall, unfortunately, be compelled to treat this subject far too briefly, as it can be treated properly only by giving long catalogues of facts. We shall, however, be enabled to discuss what circumstances are most favourable to variation. In the next chapter the Struggle for Existence amongst all organic beings throughout the world, which inevitably follows from their high geometrical powers of increase, will be treated of. This is the doctrine of Malthus, applied to the whole animal and vegetable kingdoms. As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.” From pages 4-­‐5 of the Introduction, first edition facsimile. Hardy -­‐ Weinberg Equilibrium (HWE): Worksheet The HWE computes expected future genotypic and allelic frequencies based on current allelic frequencies. [Note: HWE assumes no evolution is occurring. See page 2 for the list of HWE assumptions.] Thus, to use the HWE it is critical to first determine the current allelic frequencies. Once you know the allelic frequencies, they will not change as long as the HWE assumptions hold true. Most HWE problems come in one of two forms. 1) You are given the frequency of homozygous recessives 2) You are given the frequency of all genotypes Before we work through each of these types of problems, let’s review the basic formulas. Formula for allelic frequencies: p = frequency of the dominant allele q = frequency of the recessive allele p + q = 1 (given there are only two alleles for this gene) Given the frequency of either p or q, you can determine the frequency of the other allele: 1 -­‐ p = q or 1 -­‐ q = p Formula for genotypic frequencies (showing steps to reach the final formula): (p + q)2 = 12 (p + q) (p + q) = 1 p2 + pq + qp + q2 = 1 p2 + 2pq + q2 = 1 the form we normally use These equations tell us the expected frequencies for homozygous dominants (p2), heterozygotes (2pq) and homozygous recessives (q2) -­‐ if HWE holds true. These formulas for allelic & genotypic frequencies are all you need to work HWE problems. Example: You are told that the frequency of homozygous recessives in a population = .09 (9%) and to assume that the population is in Hardy-­‐Weinberg equilibrium. If HWE holds, then the frequency of the homozygous recessives should equal q2. 0.09 = q2 To determine q, take the square root of 0.09 = 0.3 = q Once you determine q you can determine p: 1 -­‐ q = p => 1 -­‐ 0.3 = 0.7 => 0.7 = p Now you have the allelic frequencies of p and q, and these will not change under HWE. To compute the genotypic frequencies, use these values for p & q in the equations above. The expected frequency of homozygous dominants = p2 = (0.7) 2 = 0.49 The expected frequency of heterozygotes = 2pq = 2(.7)(.3) = .42 The expected frequency of homozygous recessives = q2 = (.3) 2 = .09 You can check your work by adding the three frequencies (sum should equal one). The problems below are variations on the same theme. All give the frequency of homozygous recessives, and assume that HWE holds. They may ask for different types of answers (allelic or genotypic frequencies) but all require the same general calculations. Other variations are the way in which the information is written e.g. the frequency of recessive phenotypes may be given instead of the frequency of homozygous recessives. 1. A population in HWE contains a frequency of .16 homozygous recessives. What is the frequency of the recessive allele? What is the frequency of the dominant allele? 2. A population in HWE contains a frequency of .36 homozygous recessives. What is the frequency of the recessive allele? What is the frequency of the dominant allele? 3. One in every 10,000 people are stricken by a recessive genetic disorder. Assuming HWE, what is the frequency of this allele in the population? What are the genotypic frequencies? 4. A population in HWE contains a frequency of .49 homozygous recessives. What are the allelic frequencies? What are the expected genotypic frequencies in the next generation? 5. A population in HWE contains a frequency of .64 homozygous recessives. What is the frequency of the recessive allele? What is the frequency of the dominant allele? What is the frequency of the dominant phenotype? 6. A population in HWE contains a frequency of .01 homozygous recessives. What are the expected genotypic frequencies in the next generation? 7. A population in HWE contains a frequency of .09 homozygous recessives. What are the expected genotypic frequencies in the next generation? For more practice, pick any value for q2 and work out all the frequencies. The second type of problem typically gives you the frequencies of all the genotypes, and the population may deviate from HWE. The formulas are the same; the main difference is getting started i.e. determining the allelic frequencies. To compute allelic frequencies from genotypic frequencies I prefer to convert to actual numbers (not frequencies) and count the total number of each allele. Each homozygote contains two alleles of the same type; heterozygotes contain one of each type of allele. The total number of alleles should equal 2x the number of individuals (assumes individuals are diploid). Problem: A population consists of 16 homozygous dominants (AA), 48 heterozygotes (Aa) and 36 homozygous recessives (aa). What are the allelic frequencies? Solution: We are given numbers of individuals from the start. Now, make a table and count out alleles. ‘A’ alleles ‘a’ alleles 16 Homozyg. dominants (AA) => 16 x 2 A = 32 48 Heterozygotes (Aa) => 48 x 1 A = 48 & 48 x 1 a = 48 36 Homozyg. recessives (aa) => 36 x 2 a = 72 -­‐-­‐-­‐-­‐-­‐ Totals -­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐ -­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐ Total ‘A’ = 80 Total ‘a’ = 120 100 = Total individuals Total copies of alleles (A & a) = 200 (Note: the total numbers of alleles is double the number of individuals) Now convert these numbers into allelic frequencies: frequency of ‘A’ = 80 / 200 = .4 = p frequency of ‘a’ = 120 / 200 = .6 = q (Note: p + q = 1; .4 + .6 = 1) Once you have determined allelic frequencies, you can answer any additional questions that the problem might ask e.g. expected genotypic frequencies in the next generation. To compare the current genotypic frequencies to the expected frequencies, first you need to perform the usual calculations for expected genotypes. Second, you compare those calculated frequencies to the starting frequencies given. Preferably you would use statistics for this comparison. Alternatively, you can compare absolute values of your observed vs. expected. Do the observed values differ from those expected? Final note: Although your starting genotypic frequencies may deviate from HWE, your starting allelic frequencies cannot deviate from HWE. The allelic frequencies are simply ‘givens’. The only way that you could see a deviation in allelic frequencies is in the next generation if the allelic frequencies changed (i.e. evolution). However, you would not be able to compute this change. You could only measure allelic frequencies from generation to generation. Any significant change in allelic frequency = evolution. More Problems: 8. A population consists of 60 AA individuals and 40 aa individuals. What are the expected allelic and genotypic frequencies in the next generation assuming HWE? Is the current population in HWE? 9. A population consists of 16 AA individuals, 48 Aa, and 36 aa. What are the expected allelic and genotypic frequencies in the next generation assuming HWE? Is the current population in HWE? 10. A population consists of 26 AA individuals, 48 Aa, and 26 aa. What are the expected allelic and genotypic frequencies in the next generation assuming HWE? Is the current population in HWE? RECALL -­‐ Hardy -­‐ Weinberg Equilibrium: Measures microevolution Assumptions of HWE
Type of Microevolution
(if these assumptions are met, no evolution occurs) 1. Very large (infinite) population. 1. Genetic drift (bottleneck, founder effect) 2. Isolation from other populations (no gene flow) 2. Gene flow (migration)
3. No net mutations
3. Mutation
4. Random mating (panmictic population) 4. Assortative mating 5. No natural selection 5. Natural selection Other study ideas: -­‐ Work with your lab partner to make other combinations. -­‐ Try using phenotypic frequencies instead of genotypic frequencies. -­‐ What type of change would you expect if the population mated assortatively? -­‐ Other questions can be found at the back of Chapter 23 in your text and MasteringBio Answers to problems. 1. Given HWE, the frequency of homozygous recessives = q2 = .16. Thus, q = .4 = the frequency of the recessive allele. Frequency of dominant allele = p = .6 (1 -­‐ .4 = .6) 2. q2 = .36 therefore q =.6; p = .4 3. q2 = 1/10,000. The square root of 1/10,000 = 1/100 or .01 = q. Although this problem does not ask for the frequency of p , you need to know it to work out genotypic frequencies. p = .99 (1 -­‐ .01). Genotypic frequencies: p2 = (.99) 2 = .98; 2pq = 2(.99)(.01) = .0198 (or .02), q2 = (.01) 2 = .0001 (already given = 1/10,000) 4. p = .3, q = .7, p2 = .09, 2pq = .42, q2 = .49 5. q2 = .64; square root of .64 = .8 = q; p = .2 The third part of this question asks for the frequency of the dominant phenotype, which includes both homozygous dominant and heterozygous genotypes, or p2 + 2pq = (.2) 2 + 2(.2)(.8) = .04 + .32 = .36 6. p2 = .81, 2pq = .18, q2 = .01 (p = .9, q = .1) 7. p2 = .49, 2pq = .42, q2 = .09 (p = .7, q = .3) 8. There are 60 x 2 A’s = 120 and 40 x 2 a’s = 80 for a total of 200 alleles. Starting allelic frequencies are: p = .6 (120/200); q = .4 (80/200). If at HWE, allelic frequencies will not change: p = .6; q = .4. Expected genotypes: p2 = .36, 2pq = .48, q2 = .16 The starting population had NO heterozygotes, but HWE predicted 48%, which suggests the starting population was far from HWE. 9. Starting allelic frequencies: p = .4, q = .6; Under HWE the allelic frequencies will not change; expected genotypic frequencies: p2 = .16, 2pq = .48, q2 = .36 Starting pop. was in HWE 10. Starting allelic frequencies: p = .5, q = .5; Under HWE the allelic frequencies will not change; expected genotypic frequencies: p2 = .25, 2pq = .5, q2 = .25 Starting pop. was in HWE (or darn close!) Ring Species
The diagram below shows a partial distribution of the white-footed deermouse, Peromyscus
maniculatus. This species can be further divided into four subspecies: P. m. borealis,
P. m. nebracensis, P. m. sonoriensis and P. m. artemisiae. Note that P. m. borealis and P. m.
sonoriensis do not come into contact, but each of these subspecies mates with members of the other
two subspecies: P. m. nebracensis and P. m. artemisiae. However, while P. m. nebracensis and P.
m. artemisiae have limited contact, they do not interbreed!
Ring species like the one shown here provide material for debate, especially about the nature of a
species and species concepts. Consider the morphological species concept (MSC) and biological
species concept (BSC). How would you define each of these subspecies? Are they one species?
Two species? Four species?
Imagine that P. m. nebracensis and P. m. artemisiae become extinct. Are the two remaining
‘subspecies’ still members of the same species? Note the criteria you use depends on the species
concept applied. Be prepared for questions about species concepts and examples of ring species like
P. maniculatus.