Bio Unit 6

HOW did the overwhelming biodiversity currently present on Planet Earth arise?

"biological evolution"

Two major requirements must be met in order for speciation to occur. Describe the following and how each relates to speciation:

1) Genetic Isolation: Requires that gene flow between populations of a species is interrupted/ halted 2) Genetic Divergence: Enough time must pass to allow the accumulation of sufficient phenotypic characteristics to prevent interbreeding between the two newly distinct populations

The frequency of alleles at one locus in the gene pool of a large population is A (dominant) = 40% and a (recessive) = 60%. What would you predict is the frequency of the Aa genotype in this population when it is in Hardy-Weinberg equilibrium?

A = p = 0.4 a = q = 0.6 Aa = 2pq = 2 x 0.4 x 0.6 = 0.48

Remember - in science - the word "theory" does NOT mean "guess"

A conjecture, an opinion, a speculation or an assumption based on limited information or experience, not necessarily on facts.

Sympatric speciation

A speciation in which new species evolve from a single ancestral species while inhabiting the same geographic region.

Heterozygous

Allele Frequency 2pq Genotype Frequency Aa

Homozygous dominant

Allele Frequency p^2 Genotype Frequency AA

Homozygous recessive

Allele Frequency q^2 Genotype Frequency aa

The founder effect

Another instance involving a small population But the reason is migration, not environmental calamity or human impact E.g., colonization of an island by one or a few members of a species

Charles Darwin

As the ship's naturalist, Beagle, Darwin collected biological materials of all kinds (including fossils) from many places Collected extensively in the Galapagos Islands in the eastern Pacific Returned to England in 1836 and spent the next 22 YEARS analyzing and thinking about his specimens - and writing a book

Important to remember that if the environment changes

DIFFERENT individuals will be more "fit" and more likely to reproduce

Genetic homology

DNA sequence similarity resulting from common ancestors 90% identical amino acid sequence (encoded in the DNA) between humans and fruit flies

Evolution always leads to more complex species as a part of a progression towards the best species. a. True b. False

False

Darwin's (and Wallace's) Ideas

Idea 1: The species inhabiting the Earth have CHANGED through time Current species are descended from ancestoral species "Descent with modification" (evolution) The idea of evolution had been already been proposed earlier by others (e.g., Jean-Baptiste Lamarck and Erasmus Darwin - Darwin's grandfather) Idea 2: The means ("mechanism") by which "descent with modification" occurs is "natural selection" This was a truly novel idea - and one that resulted in revolutionizing our understanding of biological diversity and the entire discipline of biology

Explain in your own words why "survival of the fittest" is a misleading phrase, and why "reproduction of the fittest" is more accurate.

If one is able to reproduce in a given environment successfully, then that individual is demonstrating their fitness. You must reproduce and generate viable offspring in order for your genes to be passed on- aka - in order for your species to survive.

Gene Pool

In population genetics, the term evolution is defined as a change in the frequency of an allele in a population. Frequencies range from 0, present in no individuals, to 1, present in all individuals. The gene pool is the sum of all the alleles at all genes in a population.

Individuals do not evolve

Insect populations, not individual insects, evolve resistance to pesticides We can become immune to viral infections, as individuals, by individually changing patterns of gene expression to produce antibodies against the virus This is NOT evolution Individuals do NOT evolve; it is populations that evolve You, personally, will never evolve into anything else

Why is natural selection likely better to adapt a population to its environment compared to the other causes of evolution?

It maintains favorable alleles while removing unfavorable alleles for a given environment. (Page 6 of pop genetics slides.)

The bottleneck effect

Large populations of organisms have lots of genetic variability - i.e., more than one allele at most loci If most of the population is killed as a result of changes in the environment, some of that variability is likely to be lost

Define microevolution. What does it lead to?

Microevolution is the change in allele frequency over short time spans (few generations). This leads to macroevolution→ the production of new species and groups of new species.

What are the causes of evolution?

Natural Selection Non-random mating Genetic Drift Gene flow Mutation

Do natural populations ever satisfy all five of these conditions? Why or why not? Because of this, what becomes of the allele frequencies?

No. There is no perfect environment where all 5 of these conditions are met. Therefore, allele frequencies change through future generations.

Assume Hardy-Weinberg equilibrium. In the human population, the frequency of the disease cystic fibrosis is about 25 cases per 10,000 individuals. It is inherited as a recessive trait that is only expressed in homozygous individuals. Many people are carriers of this allele (heterozygous). In a random sample of 10,000 people, how many would you expect to be carriers?

Only individuals who are homozygous for cystic fibrosis will exhibit this trait, so 25/10,000 (= 0.0025) = q2 So, the square root of 0.0025 (= 0.05) = q; therefore p = 0.95 "Carriers" are the heterozygotes = 2pq (2 x 0.95 x 0.05) = 0.095 = 9.5% 9.5% of 10,000 = 950 people would be carriers

Darwin's Inference

Production of more individuals than can be supported by the environment leads to a "struggle for existence" - only a fraction of each generation's offspring survive to reproduce The struggle to survive long enough to reproduce is NOT random - those individuals whose genetic inheritance best fits them to their environment will be more likely to leave offspring Unequal ability to reproduce will lead to gradual change in the species (or a population within a species), potentially producing new species

Theodosius Dobzhansky

Prominent Biological Scientist "Nothing in Biology Makes Sense Except in the Light of Evolution

Genetic drift

Random; in small populatins

Natural Selection

Results in alleles being passed to progeny in numbers DISPROPORTIONATE to the frequencies in the parental generation I.e., leads to change (evolution) in allele frequencies - and changes in phenotype +Sexual Selection does this by maintaining favorable alleles (for a particular environment) in a population, while removing unfavorable alleles (for that environment) Sometimes referred to as "survival of the fittest" But, that really misses the point in a very fundamental way... What's actually important here is REPRODUCTION So, a much better description is "reproduction of the fittest" Text Definition: "Natural selection occurs when individuals with certain characteristics produce more offspring than do individuals without those characteristics. The individuals are selected naturally - meaning, by the environment."

Developmental homology

Similarity in embryo development resulting from common ancestors E.g., embryological similarities between birds and mammals...

Morphological Homology

Similarity in structures resulting from common ancestry E.g., the bones present in the forelimbs of mammals

Evidence of Extinction

The "Irish Elk" - one of the first species recognized to have gone extinct

Two circumstances in which genetic drift can have large effects:

The "bottleneck effect" The "founder effect" Both situations involve SMALL populations - but for different reasons

Evidence supporting the theory of evolution

The fossil record: Literally millions of fossils have been collected and analyzed The pattern of appearance, and disappearance, of certain types of fossils through time is consistent and predictable E.g., the oldest vertebrate fossils are of fish, amphibians next, reptiles and mammals in still younger rocks

Assume that in a population of birds, two alleles exist for tail color: red, which is recessive, and blue, which is dominant. You do a field study of a population of 1,000 birds, and find that 420 have red tails and 580 have blue. If the population is in H-W equilibrium, what is the frequency of the recessive allele in this population?

To be red tailed, the birds must be homozygous recessive, i.e., the frequency of red tailed birds (0.42) is equal to q2. The frequency of the recessive allele in the population = q. The square root of 0.42 = q = 0.64

For the following, assume that the population is in Hardy-Weinberg equilibrium and that there is a large population, random mating, no selection, no gene flow and no mutation. In a large population of flowering plants, the allele for red color is dominant to that for white. The frequency of the allele for red color in the population is 0.25. What is the frequency, in percent, of plants with white flowers in the population?

To have white flowers the plant must be homozygous for the recessive allele (q) q = 0.75 (i.e., 1 - 0.25) q2 = 0.75 x 0.75 = 0.56 = 56%

Allopatric speciation requires geographic barriers to promote genetic divergence and genetic isolation, whereas sympatric speciation involves the development of new species within the same geographical area. a. True b. False

True

The mechanism of evolution, natural selection, is not a random process. True or False

True (Selects for the individuals who are successful at reproducing in the environment that they are in)

2. Suppose that among a group of 50 people, 2 individuals had cystic fibrosis- a recessive genetic disease. Assuming that the population is in HWE, what is the probability that the rest of the people are carriers of the disease (i.e. Aa)? a. 0.32 b. 0.04 c. 0.20 d. 0.80

a. 0.32

What are the causes of evolution? (Hint: what are the five conditions that need to be met for HWE? What needs to happen to them?)

a. Mutations (random change in allele frequencies) b. Natural selection (leads to the change in alleles frequencies; this is non-random) c. Genetic drift d. Gene flow (migration in and out of other populations must happen) e. Non-random mating (sexual selection)

List the five conditions that must be met in order for a population to remain in Hardy-Weinberg equilibrium:

a. No mutation b. No natural selection c. No genetic drift d. No gene flow (migration) e. Random mating must occur

15. The bottleneck effect: a. Results from environmental/ human calamity and leads to a loss in the allelic variability of the population b. Involves the colonization of a new area due to migration c. Results in the loss of all genetic diversity from the gene pool of a population d. Promotes the shifting of alleles among different loci within a population

a. Results from environmental/ human calamity and leads to a loss in the allelic variability of the population

Darwin and Wallace postulated that

a. The species inhabiting the earth have changed through time b. The mechanism by which descent with modification occurs is natural selection

For the following, assume that the population is undergoing random mating, no gene flow, no mutations, no genetic drift, as well as not mutating. In a large population of beetles, the allele for a metallic exoskeleton is dominant to that for a black exoskeleton. The frequency of the allele for metallic exoskeletons in the population is 0.38. a. In percent form (%), what is the genotype frequency of the: b. What is the allele frequency of q? c. What is the allele frequency of P? d. What is q representing in this problem? e. What is P representing in this problem? i. Homozygous dominants beetles? ii. Heterozygote individuals? iii. Homozygous recessive individuals?

a. What is P representing in this problem? The dominant alleles in the gene pool (the total alleles of the metallic exoskeleton) b. What is q representing in this problem? The recessive alleles in the gene pool (the total alleles of the black exoskeleton) c. What is the allele frequency of P? 0.38 d. What is the allele frequency of q? 0.62 e. In percent form (%), what is the genotype frequency of the: i. Homozygous dominants beetles? P2= 0.382= 0.144= 14% ii. Heterozygote individuals? 2pq= 2(0.38)(0.62)= 0.471= 47% iii. Homozygous recessive individuals? q2= (0.62)(0.62)= 0.384= 38% (*a really good check- be sure your final answers/ calculations all add up close to 1 or 100%)

The founder effect: a. Results from environmental/ human calamity and leads to a loss in the allelic variability of the population b. Involves the colonization of a new area due to migration c. Results in the loss of all genetic diversity from the gene pool of a population d. Promotes the shifting of alleles among different loci within a population

b. Involves the colonization of a new area due to migration

Which of the following is a misconception of the theory of evolution? a. Evolution is both a theory and a fact b. The theory of evolution is an explanation for the origin of life on Earth c. The theory of evolution does not explain the beginning of the universe d. There are many known and well documented transitional fossils in the fossil record

b. The theory of evolution is an explanation for the origin of life on Earth

3. In a population in Hardy-Weinberg equilibrium, 1% of the individuals in a population show the recessive trait of a certain characteristic. In this situation, what is the value of p? a. 90% b. 81% c. 0.90 d. 0.81

c. 0.90

22. Which of the following is CORRECT regarding evidence in support of the "out of Africa" idea? a. Humans probably first reached the western hemisphere by ~100,000 years ago (no, 20,000) b. The oldest known fossil remains of our species are from the Middle East c. All the available evidence supports the idea that our species evolved in mid-central Africa and reach other parts of the world by migration d. The last common ancestor between humans and chimps was found to have migrated out of Africa

c. All the available evidence supports the idea that our species evolved in mid-central Africa and reach other parts of the world by migration

6. Which of the following is TRUE about the theory of evolution? a. Evolution can occur in individuals b. All species are clearly distinct from one another c. Immunity to infections and disease within an individual is NOT conferred through evolution d. Wild species are perfectly adapted to their environments

c. Immunity to infections and disease within an individual is NOT conferred through evolution

Where is the fossil missing link between humans and chimps? a. Scientists have not uncovered it yet b. Scientists have uncovered it, yet require more fossilized samples before definitively declaring the link between humans and apes c. There exists so such thing since humans and chimps have evolved extensively since our last shared common ancestor d. Scientists have uncovered it- the hominid we call "Lucy"

c. There exists so such thing since humans and chimps have evolved extensively since our last shared common ancestor

4. In a certain group of African people, 16% are born with sickle-cell disease (homozygous recessive), a disorder in which red blood cells produced do not maintain their normal biconcave shape. If this group is in Hardy-Weinberg equilibrium, what percentage of individuals is homozygous for the normal red blood cell production? Round your answer to the nearest whole percentage. a. 40% b. 16% c. 60% d. 36%

d. 36%

In a large population of bonobos, the frequency of the recessive allele is initially 0.1. There is no migration and no selection. What is the frequency of the dominant allele? Assume that there are two alleles of this gene. a. 10% b. 20% c. 50% d. 90%

d. 90%

Does meiosis and sexual reproduction change allele frequencies? a. Yes, cellular division alters the gene pool b. Yes, meiosis results in different combinations of alleles c. No, cellular division alters the gene pool d. No, meiosis only results in the different recombination of alleles

d. No, meiosis only results in the different recombination of alleles

Biological Species Concept

defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species.

Which of the following is evidence in support of the theory of evolution? a. Genetic homology b. Fossil record c. Developmental homology d. Morphological homology e. All of the above f. B & D g. A & B

e. All of the above

17. Which of the following are mechanisms of reproductive isolation? a. Post-zygotic barriers b. Allopatric speciation c. Pre-zygotic barriers d. Sympatric speciation e. All of the above f. A & C g. B & D

f. A & C

P

frequency of the dominant allele in the population

q

frequency of the recessive allele in the population

18. The biological species concept: a. Focuses on the idea of reproductive isolation b. Eludes to the idea that members of one species does not/ cannot successfully interbreed with members of any other species c. Suggests that individual species do not maintain their genetic identity d. Leads to the idea of morphology being the primary source of distinguishing between species e. All of the above f. A & C g. A & B

g. A & B

Genotype frequency

how common a certain genotype is within a population's gene pool; this term should be one that is less abstract to you- basically how frequently homozygous dominant (AA), heterozygous(Aa), or homozygous recessive (aa) individuals are within the population.

Allele frequency

how common one allele (the dominant or recessive) is within a population's gene pool; how frequently occurring is 'H'? How frequently occurring is 'h'?

Pre-zygotic barriers

is a mechanism that reduces the viability or reproductive capacity of hybrid offspring. Spatial isolation is a type of prezygotic barrier in which different species are reproductively isolated by location.

The development of the theory of evolution

is most closely associated with Charles Darwin - but others contributed and had similar ideas +He voyaged around the world on the Beagle

The theory of evolution

is the best scientific explanation we have for the DIVERSITY of life on Earth. The Origin of SPECIES, not The Origin of LIFE Darwin helped start the theory of evolution by natural selection - he didn't finish it

Population

is the study of populations of organisms, especially the regulation of population size, life history traits such as clutch size, and extinction.

Gene flow

migration - also random

Post-zygotic barriers

occur after the zygote has formed, meaning they either reduce the viability (which basically means the ability to avoid dying) or the reproductive capacity of the hybrid offspring.

Non-random mating

occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals. When the probability is the same, then individuals are just as likely to mate with distant relatives as with close relatives -- this is random mating.

Allopatric Speciation

or geographic speciation is speciation that occurs when biological populations of the same species become vicariant, or isolated from each other to an extent that prevents or interferes with genetic interchange.

p^2+2pq+q^2=1

p2 = percentage of homozygous dominant individuals q2 = percentage of homozygous recessive individuals 2pq = percentage of heterozygous individuals

Mutation

random change in allele frequency due to mutation is quite slow compared to the other four mechanisms

Reproductive Isolation

refers to the situation where different species may live in the same area, but properties of individuals prevent them from interbreeding. The things which stop species or groups of organisms reproducing sexually are called isolating mechanisms.

Reproductive isolation

refers to the situation where different species may live in the same area, but properties of individuals prevent them from interbreeding. The things which stop species or groups of organisms reproducing sexually are called isolating mechanisms.

Speciation

the formation of new and distinct species in the course of evolution.

evolution

the idea that species change through time

Evolution

the process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth.