Evolution and Population Genetics Flashcards

Question

Essentialism

Answer 1

- The physical world and its life forms are fixed - All members of a class share unchanging properties that define the class - Attributed to Greek philosopher Aristotle (384-322 BC)

Answer 2

sometimes, depending on .....

Answer 3

• Improve fitness such that organisms WITH the trait have higher fitness than those without (All other things being equal) • Show correlation between the presence of the feature and the hypothesized selective pressure Does it enhance fitness? Does its presence correspond to a specific selective regime?

Answer 4

Feeding specializations Crypsis Mate attraction or competition

Answer 5

specialized features that enhance fitness Adaptation (v) is the process by which features that enhance fitness are fixed in a population or species.

Answer 6

- The “great chain of being” | - Life arranged hierarchically, culminating in divinity

Answer 7

(Swedish,1707-1778) - Carl von Linné, botanist, father of modern taxonomy - Systema Naturae (1735) – binomial nomenclature - Hierarchical taxonomy embodied Scala Naturae - Still used today, but reflects evolutionary relationships

Answer 8

Chair and chairness The physical world and its life forms are fixed – most controversial aspect of what Darwin proposed, was that species were NOT fixed in form (fixed as unchanging) All members of a class share unchanging properties that define the class Evolutionary thinkers existed but they lacked mechanisms to drive evolution

Answer 9

(French,1707-1788) - Recognized that differences between related species living in different parts of the world reflect the different environments they inhabit - After migrating, organisms must somehow change to suit their new environment

Answer 10

(French, 1744-1829) - Philosophie Zoologique (1809) - First explicit scientific treatment of evolution Lamark proposed a mechanism, now shown to be incorrect: “internal force” (unknown) that causes parents to produce offspring slightly different from itself = accumulates changes over time, so species transform into another one. No extinction and no branching Transformism Inheritance of acquired characters - Individuals change during development - If changes are beneficial, parents transmit these acquired characters to their offspring - Famous discussion of giraffe’s neck

Answer 11

- Lineages persist forever, but change in form - Vague mechanism of “internal force” - No extinction or branching of lineages

Answer 12

(French, 1769-1832) - Paleontologist and comparative anatomist - Strong critic of Lamarck’s ideas - favored essentialism. Disputed Lamarck’s claim that forms change gradually over time Extinction - First to firmly establish extinction as fact - Rigorously reconstructed and classified fossils of mastodons and many other extinct organisms - attributed extinction to discrete catastrophic events

Answer 13

- Disputed Lamarck’s claim that forms change gradually over time - Correlation of parts – organisms are so integrated in form and function that any changes would lead to death (“irreducible complexity”)

Answer 14

James Hutton and Charles Lyell

Answer 15

(British 1797-1875) - Uniformitarianism Historical changes result from uniform geological processes that still occur today (e.g., erosion, sedimentation, volcanism) - supplanted geological catastrophism Earth is very old and is always slowly changing.Past can inform the present, and vice versa. Lyell’s ideas profoundly influenced Darwin.Could species also change gradually along with these changes to their environment?

Answer 16

James Hutton, (Scottish 1726-1797) - Gradualism Earth’s physical features gradually changed due to slow geological processes

Answer 17

Historical changes result from uniform geological processes that still occur today (e.g., erosion, sedimentation, volcanism)

Answer 18

Earth has had a complex history during which it has changed significantly in terms of its geology, topography, and inhabitants. The complexity of the Earth’s history can be explained in terms of the processes that are observed today —erosion, volcanism, etc Implications: Earth is very old and is always slowly changing. Past can inform the present, and vice versa.

Answer 19

Essentialism is dominant - Most people, including most biologists, still thought that species do not change, in part because of influential essentialists like Cuvier or Linnaeus No satisfactory theory for biological diversity - Those who favored evolution (Lamarck) had incorrect views of the process (transformism) and the mechanism (inheritance of acquired characters) Extinction and Branching - Cuvier demonstrates that extinction happens - Even those who favored “evolution” did not think species could “split” Uniformitarianism is promoted - Geologists (Hutton and Lyell) argue that the Earth is old and constantly changing, not static and unchanging as thought by essentialists - Could species also be gradually changing with their environment?

Answer 20

Did not invent the idea of evolution: he explained observations – came up with hypothesis Only later did hypo became a theory: Science is “organized skepticism”. Scientific Theories are constantly evaluated and updated: DATA Scientists would discard the Theory of Evolution if it were inconsistent with observations New discoveries (DATA) in biology continue to validate the Theory of Evolution SO FAR….no tested hypotheses or observations have negated the Theory of Evolution He proposed a mechanism for evolution: Natural selection Descent with modification is the outcome of evolution Came up with a hypothesis to explain evolution Catalog of evidence supporting decent with modification: (THE FACT OF EVOLUTION) Proposed natural selection : (MECHANISM OF EVOLUTION) The Beagle arrived at the Galapagos in 1835.

Answer 21

Modern species, in at least some cases, resemble fossils Modern domesticated animals can be made to vary through intentional selection (artificial selection) The creatures in archipelagos vary from island to island Organisms may have very complex modifications that are necessary for their survival

Answer 22

Unlike wild species, most varieties are freely inter-fertile Closely related varieties show more pronounced morphological differences than closely related wild species Common opinion among animal and plant breeders held that domesticated varieties arose from wild ancestors that had the same or similar characteristics as the domesticated variety In other words, each variety is descended from a unique ancestral species. Domesticated pigeons resembled only one wild species …

Answer 23

new varieties arise by preferentially breeding individuals showing specific desirable traits. Traits arise as random “sports” that are then selectively bred. This process occurs over many generations, not in a single step “Improvement” of breeds is a continual process, resulting in the accumulation of fairly significant modifications in a relatively short period of time

Answer 24

The Beagle arrived at the Galapagos in 1835. Darwin did not pay much attention to the finches after leaving the Galapagos.The following year (in 1837), the ornithologist John Gould made a descriptive account of the Galapagos collections, with the surprising opinion that the finches belonged to the SAME family. Close observation showed a wide range of variation in the size and shape of the beaks; These differences correlated with feeding preferences Each feeding type has a characteristic range of beak shapes. The 13 species of finches found on the Galapagos comprise the same number of feeding types as 9 FAMILIES of birds in South America. The Galapagos Islands have a harsh, arid climate, characterized by extended periods of severe drought. Annual cycles: hot, wet winters, cooler, dry summers. Multi-year cycles of extreme droughts (ENSO).

Answer 25

(1766-1894) “An Essay on the Principle of Population, as It Affects the Future Improvement of Society, with Some Remarks on the Speculations of Mr. Godwin, M. Condorcet, and other Writers.” (1798, published anonymously) Usually referred to as the “Essay on Population” Premise: Left unchecked, human reproduction rates will rapidly outpace resource production, leading ultimately to “crime, disease, war, and vice.” (these being “natural” checks on population growth)

Answer 26

Thomas Robert Malthus Reproductive potential AND reproductive effort GREATLY exceed requirements of reproductive replacement At the point where population size outstrips resource production, there are only two alternatives: find the means to expand the resource pool, or DIE. WHICH organisms survive has to do with interactions among organisms, and between organisms and their environment

Answer 27

In periods of drought, favorable resources (e.g. soft buds and seeds) are quickly depleted, leaving only less favorable food (hard, tough seeds, etc.) Only those birds with beaks capable of breaking these tough food items can survive. Death of “unfavorable” birds readjusts population size to the available resource pool. “Favorable” beak morphologies are passed on to offspring Very small morphological changes accumulate over a long period of time, leading to eventual (morphological) divergence of populations Widely differing morphologies gradually become reproductively incompatible "Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.” C. Darwin “The Voyage of the Beagle” (1845)

Answer 28

Variation: “Individuals within species are variable.” Inheritance: “Some of these variations are passed on to offspring.” Differential survival: “In every generation, more offspring are produced than can survive.” Extinction: “The survival and reproduction of individuals is not random. Individuals who survive and reproduce are those with the most favorable variation...”

Answer 29

Common descent Gradualness of change over time Population differentiation Natural selection

Answer 30

All living things part of a community of descent. Organisms that are more closely related (have a more recent common ancestor) more similar than those that are more distantly related

Answer 31

Differences among organisms have accumulated in small increments over a long time Outgrowth of his “uniformitarianist” perspective

Answer 32

Changes in species reflect changes in the proportion of individuals in a population bearing certain hereditary traits Changes in species take place at the level of individuals within population Talking here about variation among individuals Not a sudden origin of new species, or transformation of individuals VARIATION, NOT TRANSFORMATION

Answer 33

Population differentiation caused by differential reproductive success of individuals bearing particular traits Individuals that have more success are those better able to use resources in a particular habitat Same principles independently derived by Alfred Wallace during his work in Malaysia

Answer 34

Professional “curiosity” collector Wrote a paper on natural selection in 1858 and sent it to Darwin. A year later Darwin published “Origin of the Species” We cannot talk about the history of Darwin without mentioning his nemesis, Into this historical setting there stepped a man whose role in the history of biology is enigmatic and often under appreciated, Alfred Russell Wallace. Wallace was a poor man of limited education who had to struggle just to get by. He earned his living by voyaging to places like South America and the Far East and collecting many Maybe he didn't want to arouse controversy. Maybe he was afraid to offend many peoples religious sensibilities. Anyway, what happened next is a fascinating story. Wallace, racked with a high fever in the tropics of Southeast Asia came up with the concept of natural selection. The idea that all organisms were engaged in a struggle for existence, and the survivors were those that went on to populate the world. Those that tended to survive and give rise to future generations were more fit or better adapted to the environment than those that didn't make it. Thus, the earth's flora and fauna changed through time. After Wallace recovered from his fever, he wrote a paper on this topic and sent it to Charles Darwin whom he didn't know but had heard of, asking him to present it at a prestigious English scientific meeting. The year was 1858. Darwin, upon receiving the manuscript, went into a state of shock. Here was someone who had come up with what he thought was his idea alone. He realized the scope of all those years of work and thought during which he had not published. Then, Darwin went feverishly went to work writing. He first took Wallace's paper and added to it a long section of his own. He added his name to the paper as a co-author and then he included a letter signed by 2 famous scientists of the day describing how he had been thinking of these ideas long before Wallace, and then the paper was read at the meeting and published, while Wallace was in Asia. A year letter, "On the Origin of Species by Means of Natural Selection or the Preservation of Favored Groups in the Struggle for Existence was Published". What is typically referred to as Darwin's Origin of the Species. Darwin received almost all of the credit for the idea of Natural Selection described in the book and he also received the credit for convincing people that evolution by common descent had occurred. The moral is, never ask somebody you don't know to read something to an audience when you can't make it there. The interesting things is that Wallace and Darwin became friends. Wallace was very magnanimous, that is, he didn't feel like he didn't need to get credit, or he was very stupid. Basically he appreciated the fact that Darwin gave him any credit at all. In those days, if you were poor in England you had little prospect for success, and Darwin's money and prestige made it easier for him to obtain most of the credit at the expense of Wallace, but also, I think, made the idea more palatable to the general public who could understand how a rich, well known gentleman scientist could come up with a great idea but would sadly probably not be able to understand how some poor unknown came up with a great idea. It's sad, but things still can work like this in science. In the end, it might be hypocritical to fault Darwin. How many of us, in the face of seeing 18 years of work down the tubes, when given the opportunity to obtain credit for an idea wouldn't have done what he did. In the end, it's best to view Darwin like any other great thinker. He was human and therefore flawed. Those who came before him had created an atmosphere in which ideas on evolution could be accepted. He was smart, and in the right place at the right time, which sure beats being in the wrong place at the wrong time.

Answer 35

The general idea of evolution - Controversial among the general public - Scientists generally accepted evolution per se Darwin’s particular concept of evolution - Controversial among scientists, most of whom envisioned “progressive” change - Darwinian evolution based on lineage splitting, NOT inherently “progressive” towards higher forms Darwin’s Mechanism of Natural Selection - Generally rejected by scientists - One important flaw was the lack of a mechanism for heredity At this point, however, there are still two serious gaps in our knowledge: By what mechanism does inheritance occur? How is variability generated in populations?

Answer 36

Darwin lacked a theory of inheritance For lack of a better alternative, Darwin favored blending inheritance: New variant arises and is favored by natural selection. Offspring are intermediate. Trait spreads, but is further diluted. After many generations, trait is prevalent but blended away. There are naturally existing differences in a population (=variation) • More offspring are produced than can survive • Organisms with favorable variation will be preserved (i.e., will leave more offspring) • Accumulation of differences over time leads to adaptive radiation Darwin’s Main Interest…. • Establishing Natural Selection as the mechanism for Evolution (On the Origin of Species by Means of Natural Selection,or the Preservation of Favored Races in the Struggle for Existence)

Answer 37

Variation is the raw material for evolution by natural selection Natural selection is a sorting process of differential survival & reproduction Without variation, there can be no evolution! Genetics and environment both contribute to variation.

Answer 38

Variation: “Individuals within species are variable.” Inheritance: “Some of these variations are passed on to offspring.” Differential survival: “In every generation, more offspring are produced than can survive.” Extinction: “The survival and reproduction of individuals is not random. Individuals who survive and reproduce are those with the most favorable variation...”

Answer 39

Multiple forms within a species | (ex: polymorphism)

Answer 40

variation in phenotypic traits such as body weight or height in which a series of types are distributed on a continuum rather than grouped into discrete categories. Compare discontinuous variation. (Ex: Beak depth in Galapagos finches, height)

Answer 41

Darwin favored pangenesis – all cell lines contribute to gametes

Answer 42

Evidence favored Weismann’s germplasm theory (germ vs. soma)

Answer 43

Mechanism of transmission Born in Hyncice, Moravia (Austria); educated at the Institute of Philosophy, Olomuc (Czech Republic) Joined the Augustinian Order of St. Thomas in Brno (Czech Republic) at 21 years of age. Influenced by Darwin’s work on plant and animal domestication. Objective: “...to observe these variations in the case of each pair of differentiating characters, and to deduce the law according to which they appear in successive generations.”

Answer 44

Provides theory of heredity - genes are preserved during development - genes are passed unaltered to offspring - organism can “carry” gene without expressing phenotype - phenotype may be intermediate, but genes do not “blend” Dominance Segregation Independent assortment

Answer 45

Blending – Rare variants are blended out of the population Mendelian – Rare variants can persist and become established in the population

Answer 46

Readily available. Self-pollinating, true breeding Obtained 34 cultivars, pure breeds displaying seven selected characteristics including “...form of the ripe seeds” (wrinkled, round) “...form of the seed albumin” (green, yellow) “...position of the flowers” (terminal, axillary) “...length of the stem” (tall, dwarf)

Answer 47

22 uniform cultivars with contrasting characteristics were crossed over several generations. - Rather than hybridize species and varieties that differed in many traits, he limited his studies to the examination of single isolated traits. Kept accurate and detailed records of all crosses. - Each resultant plant was examined independently. Recognizing that chance influences mathematical power, Mendel designed his experiments to include many replicates.

Answer 48

“Henceforth in this paper those characters which are transmitted entire, or almost unchanged in the hybridization, and therefore in themselves constitute the characters of the hybrid, are termed the dominant, and those which become latent [i.e. hidden] in the process recessive.”

Answer 49

“In this generation there reappear, together with the dominant characters, also the recessive ones with their peculiarities fully developed, and this occurs in the definitely expressed average proportion of three to one, so that among each four plants of this generation three display the dominant character and one the recessive.”

Answer 50

When 2 unlike unit factors (alleles) are present in an individual, one factor is dominant and its trait is preferentially expressed

Answer 51

Disrupts nerve function, loss of control over body and mind, then death Why is it dominant? Mutant gene with extra CAG: abnormal protein with extra Glutamine This mutant protein is produced even if only one allele is present, and the toxic protein disrupts function

Answer 52

Neurological impairment (often resulting in death) due to the accumulation of gangliosides (fatty acid derivatives) in neurons of the brain Why is it recessive? Mutation of HEXA gene on chromosome 15: abnormal form of enzyme hexosaminidase A This abnormal form cannot catalyze degradation of gangliosides Even if only one normal gene is present, sufficient enzyme can be produced to catalyze ganglioside degradation

Answer 53

The two members of a gene pair segregate randomly and equally into the gametes, which then combine randomly and equally to form the next generation. During gamete formation, paired unit factors (alleles) segregate randomly so that each gamete receives one or the other.

Answer 54

The inheritance of traits is determined by "factors" (= genes) that are passed on to descendents unchanged. Alternative versions of genes (alleles) account for the variation in inherited characters. An individual inherits one such unit from each parent for each trait. The two members of a gene pair segregate randomly and equally into the gametes, which then combine randomly and equally to form the next generation. A trait may not show up in an individual, but can still be passed on to the next generation.

Answer 55

Characteristics are inherited independently of each other. Dominant traits can appear in combination either with other dominant traits or with recessive traits.

Answer 56

During gamete formation, segregating pairs of unit factors (alleles) assort independently of other pairs (e.g. color and shape are independent) EX: Female gametes from genotype RrYy Whether a gamete contains R or r has no impact on whether the gamete also contains y or Y

Answer 57

(1875-1967) Considered the “father” of genetics as a scientific discipline. Combined Mendel’s laws with statistics. Experimented with peas and poultry to verify Mendel’s findings. Creator of Punnett Square as method to visualize allele combinations.

Answer 58

(1861-1926) Vocal proponent of Mendel’s laws of inheritance. Translated Mendel's work into English (1901). Coined the terms “genetics,” “allelomorphs” (shortened to “allele”), “heterozygote,” and “homozygote.” Established the Cambridge School of Genetics. Collaborated with Punnett on genetic experiments

Answer 59

alternative form of a gene

Answer 60

a cross of an unknown genotype with the recessive genotype. Used to ascertain the identity of the unknown.

Answer 61

is the ultimate source of all heritable variation

Answer 62

alter single nucleotides

Answer 63

Substitution of a thymine (T) for an adenine (A) in the gene for B-globin If there’s a thymine, then the 6th amino acid is valine rather than glutamic acid The change in primary protein structure has implications for quaternary structure, and the RBC is misshapen

Answer 64

alters larger sections of DNA

Answer 65

shuffles existing variation into new combinations Create new combinations that lead to greater levels of phenotypic variation

Answer 66

TRUE New mutations or recombinations have no inherent tendency to result in adaptation…they are random with respect to adaptation Given that organisms are adapted to begin with, these changes are more likely to be nonadaptive or even maladaptive than adaptive! However, mutation and recombination can be nonrandom at the molecular or chromosomal level certain nucleotide substitutions more likely than others (e.g., purine to purine, etc)

Answer 67

Mutation acts on existing genes, modifying or generating new alleles Impact may be large, or very small ~Mutation in regulatory gene or other critical genes may cause early death ~Redundancy in genetic code means not every substitution specifies a new codon (silent mutations)

Answer 68

Nothing! Mutations happen because of sloppy copying, DNA degradation, and other random processes. Although generated thru random processes, mutations may not be propagated or inherited randomly ~Many (most?) mutations cause no effect or are deleterious and cause organism to die before birth

Answer 69

The bacterium remaining is not susceptible to treatment. It will divide and grow, with all daughter cells also having resistance. More treatment by same antibiotic will have no benefit. The mutation that provides resistance is generated randomly. Its spread through the population isn’t random, though—it is a predictable response to a set of circumstances. Pesticide resistance works on the same principle

Answer 70

means that both alleles are expressed, and the heterozygote manifests a third phenotype with properties of both alleles ~Both alleles are expressed: Blood Types Blood type A IAIA Blood type B IBIB Blood type AB IAIB

Answer 71

Heterozygote results in a third unique phenotype. Alleles are “blended”together ~Red and white flowers produce a heterozygous pink flower

Answer 72

A single gene impacts two or more (seemingly unrelated) traits EX: Holt-Oram (“hand & heart”) syndrome

Answer 73

Defective allele for TBX5 | Malformation of upper limbs, abnormal septa in heart

Answer 74

One gene interferes with the expression of another gene Ex: Albinism

Answer 75

If animal is homozygous recessive (cc) at albinism locus, it’s an albino and all other colorations are phenotypically “suppressed” This occurs because albinism alleles disrupt production of melanin pigment and other phenotypes are not distinguishable without melanin Example of epistasis.

Answer 76

Pleiotropy: one gene with multiple phenotypic effects Epistasis: two genes contribute to one phenotype

Answer 77

Several genes may make products that contribute to phenotype (= polygenic traits) Genes encode different elements of the enzymatic pathway, or products that interact to generate phenotypic effect Traits where phenotype is determined by interaction of multiple genes Example: eye color

Answer 78

Environment in which organism grows and matures determines degree to which genetic “potential” is realized Example: Temperature within the nest determines sex of turtle species.

Answer 79

Special case of environmental effects Environmental features that can be attributed to mother Environment of womb/egg Amount of yolk in egg Post birth maternal care

Answer 80

~Controlled crosses Determine whether phenotypes are inherited according to expectations of Mendelian laws ~Common garden experiments Raise offspring under identical conditions Run several “gardens” to test effect of particular variables ~Cross fostering Common gardens for animals Have offspring reared by parents other than their own

Answer 81

Observation: hunting prowess runs in families—the best hunters are related to one another, and there is a significant difference in ability between members of one family group and another. Hypothesis: Hunting skill is genetic. Alternatively, it is learned by children through interaction and observation of parents. Null Ho: Hunting ability is determined by parentage. Break up litters at birth, randomly re-distribute young among family groups Evaluate hunting prowess: is there a correlation between birth family and hunting prowess?

Answer 82

Genotype + Environment | This accounts for variation

Answer 83

is the proportion of variation that can be attributed to genotype Heritability is high when environmental variation is low Indicates fidelity of trait transmission (and thus how readily evolution can act on attribute)

Answer 84

Variation of the phenotype = the Variation of the environment + the Variation of the genotype. Heritability squared = Variation of the genotype divided by the Variation of the phenotype .

Answer 85

Heritability determines the response to selection. Higher heritability means stronger response. If a trait is perfectly heritable (h^2 =1), then ALL of the impact of selection will be observed (perfect fidelity)

Answer 86

Highly variable in the timing of reproduction. Is this variation genetic or environmental??? Calculated h2=0.3 for phenotype “time of egg laying” Selection acts on genetic component of this variation, favoring female “readiness”

Answer 87

Characteristics of each population will determine how or when a species will outstrip the ability of the community to support it Fate of a population hinges on characteristics related to reproduction because that’s what determines its growth rate Reproductive potential AND reproductive effort GREATLY exceed requirements of reproductive replacement

Answer 88

``` Genotype frequencies (p + q)^2 = 1 ... (Dominant allele + recessive allele)^2 = 1 ``` Allele frequencies p + q = 1 The frequency of the dominant allele PLUS the frequency of the recessive allele equals 1. To represent the diploid condition, you square the whole thing. ``` p= frequency of the dominant allele q= frequency of the recessive allele ```

Answer 89

``` 5 Assumptions Mating is random No natural selection Large population size (infinite) No new mutations No migration ``` All offspring have an equal chance of survival and reproduction = no selection Large population size: Random events will have a large impact on small populations Note that under Hardy-Weinberg assumptions, allele frequencies do not change…We are predicting genotype frequencies from these allele frequencies. Genotype frequencies in the absence of selection will “go to” Hardy-Weinberg equilibrium The frequency of alleles in the next generation (g+1) depends on the frequency of alleles in the present generation (g) If you add (or subtract) genotypes in the present, it will change the frequency in subsequent generations: Mutation!

Answer 90

Allows us to derive expected frequencies of alleles, genotypes, and phenotypes when particular conditions are met Provides a set of expectations against which to evaluate observed data and thus a means of assessing possible causes of change in population. What good is Hardy-Weinberg if these assumptions are usually violated? 1. Historical and conceptual importance: H-W gives a mathematical demonstration that Mendelian inheritance preserves genetic variation 2. As a null hypothesis: H-W tells us what would happen without assortative mating, natural selection, migration, and mutation - If a population deviates from H-W, something interesting is happening

Answer 91

All offspring have an equal chance of survival and reproduction: Natural selection Large population size: Genetic drift No new alleles: Mutation and migration Random mating: Sexual selection, Geographic variation and clines If you don’t see Hardy-Weinberg equilibrium, then you can infer that one (or more) of these conditions is not being met.

Answer 92

The appearance or performance of an individual is the product of its genotype, in concert with its environment. Gene-level variability is generated thru random processes, but its inheritance is not necessarily random. The environment in which an organism lives is variable and typically limiting with respect to some resource.

Answer 93

is the nonrandom differential survival AND reproduction of particular phenotypes 2nd component of “evolution by natural selection” (1st is the origin of genetic variation) Strength of selection depends on the heritability (h^2) and on the degree of difference in fitness among phenotypes Requirements: Phenotypes have heritable basis Phenotypes have varying consequences for fitness The larger Vg is relative to Vp, the more effective selection will be

Answer 94

Fitness is determined by the reproductive output (R) for each genotype, the average reproductive output (R) of all organisms bearing the genotype. Because of environmental effects, R will not be uniform among all bearers of a genotype Defined for a genotype Pertains to a particular situation: a certain place, at a particular time The average R of the entire population (all genotypes) determines population fitness

Answer 95

~How many eggs are produced? Genotype Environment ~What is the probability of fertilization? Genotype Environment Reproductive output of a genotype is the individual effort of all organisms bearing that genotype. If the impact of environment is small, then there will be less variance in output among bearers of a genotype.

Answer 96

Balancing act with tradeoffs in costs and benefits High # of propagules incurs a high energy investment for ♀, so each typically gets less yolk or care Low investment per propagule may decrease survival rate

Answer 97

In biology, a propagule is any material that is used for the purpose of propagating an organism to the next stage in their life cycle via dispersal. The propagule is usually distinct in form from the parent organism.

Answer 98

``` # individuals having offspring # of reproductive propagules ``` [# of reproducers] x [# of eggs] = upper limit on reproductive output per cycle Number of cycles per year (Annual, seasonal, lunar cycles) AND number of cycles per female lifespan (Age of sexual maturity, Age of sexual maturity, Fertility and fecundity change over time) influence population growth rate Reproductive senescence before death? Can effect reproductive output of the population Do females have young throughout adulthood or do they pass to non-reproductive status after a certain age (or number of eggs)? Death rate of adult males and females Survival rates of propagules How many offsping survive?

Answer 99

``` # reproductive females # offspring per cycle # cycles per unit time # cycles per female lifetime Death rate of reproductive individuals Survival rate of offspring ``` Changing any of these factors will change population growth profile

Answer 100

Density-independent factors Effect is the same regardless of population size or density Density-dependent factors Effect is modulated depending on population size or density Both limit the natural, genetically determined potential for population increase

Answer 101

``` Environmental phenomena (Drought, long winters, etc.) ``` Increase mortality across the population, thus decreasing the # of reproductive females

Answer 102

~Supply of food or other resources Resources not limited for smaller populations but may become limiting as population increases ~Disease Disease may be spread more effectively Pathogens or predators may increase in #, in response to increase in prey density Density-dependent factors integrate resource availability and competition with population growth. Inter- and intraspecific interactions become critical.

Answer 103

Viability: Probability that individual bearing genotype will survive Fecundity: Number of gametes per individual Mating success: Number and quality of mates Gamete viability: Alleles impact the longevity or quality of the egg or sperm Fertilization success: Alleles impact the probability that fertilization will take place “Fitness” is the sum of fitness components at each of these stages

Answer 104

Probability that individual bearing genotype will survive

Answer 105

Alleles impact the longevity or quality of the egg or sperm.

Answer 106

Alleles impact the probability that fertilization will take place

Answer 107

In “survival of the fittest,” “fittest” means the best among known geno- or phenotypes and pertains to a particular phenotypic variable or task. We cannot easily know “absolute fitness” because we can’t tell whether a genotype or phenotype is optimal Because fitness is relative and particular to certain selective conditions, it changes!

Answer 108

reduction in fitness relative to best genotype (s) - Always a value between 0 (0 = no selection) and 1 (1 = complete mortality) - If s = 0, this is equivalent to Hardy-Weinberg assumption of no selection

Answer 109

In “survival of the fittest,” “fittest” means the best among known geno- or phenotypes and pertains to a particular phenotypic variable or task. We cannot easily know “absolute fitness” because we can’t tell whether a genotype or phenotype is optimal. Differences in fitness generate differences in the successful transmission of alleles. Because fitness is relative and particular to certain selective conditions, it changes! Violates the expectation of the Hardy-Weinberg equation that allele frequencies will be constant. Genotypes that leave proportionally more offspring will contribute more alleles to the next generation.

Answer 110

R of AA = 0.5 R of Aa = 1.5 R of aa = 0.25 ``` W(AA) = (0.5)/(1.5) = 0.333 W(Aa) = (1.5)/(1.5) = 1.000 W(aa) = (0.25)/(1.5) = 0.167 ```

Answer 111

relative measure of survival and reproduction (W) - Fitness of “best” genotype (AA, Aa) = 1 - Fitness of other genotype (aa) = 1 – s Note: this does NOT mean that AA and Aa genotypes have 100% chance of survival, only that aa has a relatively lower chance of survival. W(i) = fitness of genotype i, relative to that that of most fit genotype. W + s= 1 Divide R of each genotype by that of most successful genotype.

Answer 112

....you still have equal frequencies for p and q (both 0.5)

Answer 113

- non-random process through which pre-existing variation is sorted Survival probabilities different; reproductive probability same

Answer 114

individuals at one extreme of the range of phenotypes are fittest Taller birds fitter than shorter birds Directional selection will act to reduce # of recessive alleles Recessive allele will be reduced in frequency but not eliminated

Answer 115

2 or more discontinuous phenotypes are fittest Homozygous phenotypes fitter than heterozygote Disruptive selection will maintain allele frequencies but not phenotype frequencies Frequency of heterozygote reduced. - Heterozygote persists as long as there is random mating Allele frqs may not change

Answer 116

intermediate phenotype is fittest Heterozygote phenotype fitter than homozygotes Frequency of homozygotes reduced. Reduces the variance around the mean phenotype. Do you expect changes in allele frequency? Stabilizing selection often involves a balance between conflicting selective pressures. Example: Higher birth weight has higher cost in terms of maternal resources. Gestational diabetes, stress on baby’s organs may be incurred at higher birth weight. Lower birth weight has high cost in terms of baby’s health.

Answer 117

Cystic fibrosis is a recessive condition carried by 1 out of 25 people of European descent Mutant protein results in problems maintaining intercellular fluid levels. Heterozygotes have some protection against cholera. Sickle cell anemia is a recessive condition carried by 1 in 13 African Americans. Mutant red blood cells clog blood vessels. Heterozygotes have resistance to malaria.

Answer 118

Cystic fibrosis is a recessive condition carried by 1 out of 25 people of European descent. Mutant protein results in problems maintaining intercellular fluid levels. Heterozygotes have some protection against cholera. Sickle cell anemia is a recessive condition carried by 1 in 13 African Americans. Mutant red blood cells clog blood vessels. Heterozygotes have resistance to malaria.

Answer 119

When selection acts to eliminate a phenotype or genotype, selection is negative.

Answer 120

Fitness of a genotype is relative to its frequency in the population. Selective regime and its impact differ depending on the frequency of pheno- or geno-types. - Host-parasite systems - Immune responses to pathogens - Batesian mimicry Ex: Lake Tanganyika scale-eating fish

Answer 121

Selective regime does not depend on the frequency of the allele in the population

Answer 122

Natural selection and Balanced polymorphism: - Heterozygote advantage - Negative frequency-dependent selection - Environmental heterogeneity - Disruptive selection (can be result of environmental heterogeneity)

Answer 123

Malformed (sickle) red blood cells due to genetic variant of α-hemoglobin. Inherited as a recessive trait (AA) = normal, (aa) = sickle cell. Sickle cells block capillaries, cause anemia, 80% pre-reproductive mortality Yet it persists (10%) in some populations and causes ~ 100,000 deaths/year Why does this highly lethal disease persist? ``` Malaria is a highly lethal disease caused blood parasites (Plasmodium) ``` ``` Normal RBCs (AA) are vulnerable to infestation by Plasmodium (malaria bug) ``` ``` Sickle cells (aa) are not vulnerable to Plasmodium; but cause sickle cell anemia ``` What about heterozygotes? (Aa) RBCs usually normal, unless O2 concentration drops, then they sickle. When Plasmodium enters RBC, it destroys hemoglobin, causing drop in O2 and sickling Sickling kills Plasmodium in the cell, but leaves uninfected cells intact Host survives because most RBCs are uninfected and carry O2 normally Balanced polymorphism Heterozygote advantage maintains both alleles in populations where malaria is present One consequence is that many individuals will suffer from sickle cell anemia in these populations The prevalence of sickle cell anemia is high in the “malarial zone” e.g., Equatorial areas with plenty of mosquito vectors. Without natural selection due to malaria, the heterozygous advantage would be lost

Answer 124

What happens if Heterozygote is most fit. - Fitness: AA = 1 – s Aa = 1 aa = 1 – t Three possible equilibria: 1. A goes to fixation (p = 1, q = 0) 2. a goes to fixation (p = 0, q = 1) 3. balanced polymorphism: - chance of death for an A gene = chance of death for an a gene These are equilibrium allele frequencies where both homozygotes have lower fitness than heterozygotes.

Answer 125

- Fitness declines as the genotype becomes more common | - Maintains polymorphism

Answer 126

- Fitness increase as the genotype becomes more common | - Eliminates polymorphisms

Answer 127

Lizards and the rock-scissors-paper game - Uta stansburiana males are polymorphic for throat color (red, blue, or yellow) - Each type of male also has a different mating strategy - Throat color is heritable: OBY locus (3-allele system)

Answer 128

Brown anole (Anolis sagrei) Males exhibit 2 fitness optima corresponding to 2 “habitat niches Small limbs – suited to narrow perches Large limbs – suited to broad perches

Answer 129

Multiple “strategies” are possible: Disruptive selection may reflect environmental heterogeneity, as in the case of Brown anoles where two “niches” are present (narrow twigs vs. broad trunks). Beak size in seed-cracker finches... Discrete polymorphism for beak size: Small-billed individuals specialize on small, soft seeds Large-billed individuals specialize on large, hard seeds Intermediate beak size is selected against because it is inefficient for cracking both large and small seeds Unlike Darwin’s Galapagos finches, there are no individuals with intermediate beak sizes in the African black-bellied seed cracker. Peppered moths How could environmental heterogeneity allow both melanic and peppered moths to exist in balanced polymorphism?

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specialized features that enhance fitness; the process by which features that enhance fitness are fixed in a population or species

Answer 131

Feeding specializations Crypsis Mate attraction or competition

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crypsis is the ability of an organism to avoid observation or detection by other organisms

Answer 133

Improve fitness such that organisms WITH the trait have higher fitness than those without (All other things being equal) Show correlation between the presence of the feature and the hypothesized selective pressure

Answer 134

Differential reproductive success and survival are the effect of differences in fitness Because of linkage among traits (pleiotropy) and passage of time, it can be complicated to evaluate WHAT selection has selected FOR (and thus it can be hard to determine whether something is an adaptation)

Answer 135

Are individuals variable? YES: Broad range of beak depths in a single population Is variation heritable? YES: Parents with large beaks have offspring with large beaks Is there a struggle for existence? YES: More offspring are produced in 1975 than actually survive to 1978. Is there differential survival? YES: Finches with larger beaks are (on average) more likely to survive. Possible mechanism: Mortality coincides with decline in seed abundance due to a severe drought in 1977. Suggests that seed availability could be an important selective pressure. Does this selection act on beak size? ~Why was there differential survival? Change in environmental conditions - During drought, large seeds were much more abundant than small seeds Note that natural selection is not necessarily constant through time: It may occur only under certain environmental conditions (e.g. drought).

Answer 136

Were the 4 conditions for natural selection met? 1. Individuals in a population are variable - YES 2. Some of this variation is heritable - YES 3. A struggle to survive and reproduce - YES 4. Differential survival and reproduction - YES What does this demonstrate? 1. Natural selection can act on beak size 2. Beak size can evolve in response to relevant selective pressures, such as the availability of various food types What is left unanswered? Dozens of interesting questions about how and why the finches as a group evolved such diversity in form and behavior…

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Evolution and Population Genetics Flashcards

History of Evolution, Variation, Inheritance, Hardy-Weinberg, Malthus, Mendel, Population Genetics, Selection and Fitness.

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