Microevolution: Unique Gene Pools It is likely that you taught first-year biology students about the “peppered moth”. Prior to starting this unit, assign students a task. Have them go to this website http://www.techapps.net/interactives/pepperMoths.swf and work their way through the components of the animations. The site is very well done and it will serve as nice introduction as well as a good review of basic evolutionary concepts and how man and the environment impact natural selection.

Learning Objectives Explain the how Lamarck, Lyell and Malthus influenced Darwin’s thinking. Describe the four parts of the theory of natural selection. Explain why natural selection works on phenotypes and NOT genotypes. Explain why natural selection CANNOT occur without inheritable genetic variation.

Learning Objectives Name the two sources of genetic variation. Explain why mutations are not the most common source for genetic variation. Describe the 5 different types of mutations and explain the possible outcomes of each. Provide an example of each. Explain the difference between artificial and natural selection. Explain why pseudogenes are referred to as “junk DNA.

What is evolution ? Descent with Modification Earth’s many species are descendants of ancestral species that were very different from those alive today. Evolution change over time in the genetic composition of a population.

Charles Darwin Charles Darwin (1809-1882) is credited with proposing that the mechanism for the process of evolution is natural selection. Darwin spent five years on a voyage that took him around the world with the majority of his time spent in South America and its neighboring islands. Darwin published his theory with compelling evidence for evolution in his 1859 book On the Origin of Species, overcoming scientific rejection of earlier concepts of transmutation of species. http://en.wikipedia.org/wiki/Charles_Darwin contains FAR more information about Charles Darwin.

Jean Lamarck (1744-1829) 1. Theory of desire - organisms change due to inborn desire to change to become more fit for environment ex: ant eaters develop long snouts 2. Theory of use and disuse - organs that are being used get large and strong - organs that are not used shrink and eventually disappear ex: snakes- didn’t use legs so disappeared 3. Theory of inheritance - acquired traits were passed on to offspring ex: snakes that lost legs passed trait Importance: Recognized that species evolve, although explanation was flawed

Thomas Malthus More babies born than deaths Consequences of overproducing within environment: war, famine, disease Struggle for existence Thomas Malthus (1766-1834)

Charles Lyell Charles Lyell 1797-1875 Leading geologist during Darwin’s time Gradualism: mechanisms of change are slow and constant over time.

Charles Darwin He established that all species of life have descended over time from common ancestors, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection, in which the struggle for existence has a similar effect to the artificial selection involved in selective breeding. http://en.wikipedia.org/wiki/Charles_Darwin

Charles Darwin By the 1870s the scientific community and much of the general public had accepted evolution as a fact. However, many favored competing explanations and it was not until the emergence of the modern evolutionary synthesis from the 1930s to the 1950s that a broad consensus developed in which natural selection was the basic mechanism of evolution. In modified form, Darwin's scientific discovery is the unifying theory of the life sciences, explaining the diversity of life. http://en.wikipedia.org/wiki/Charles_Darwin

Figure it out with a partner!! Selection acts on phenotype. Explain why differential reproduction and survivorship depend on phenotype not genotype. Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

Figure it out with a partner!! Natural selection acts on individuals. Explain why only populations evolve and NOT individuals. Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

Microevolution: Unique Gene Pools It is likely that you taught first-year biology students about the “peppered moth”. Prior to starting this unit, assign students a task. Have them go to this website http://www.techapps.net/interactives/pepperMoths.swf and work their way through the components of the animations. The site is very well done and it will serve as nice introduction as well as a good review of basic evolutionary concepts and how man and the environment impact natural selection.

Evolution Terms Boot Camp Genes ~ sequence of DNA nucleotides that code for a trait Alleles ~ alternate versions of a trait. Ex: B = brown; b = blue Genotype ~ the set of alleles for a trait. Ex: Bb Phenotype ~ physical manifestation of a trait. Ex: Blue eyes Gene Pool ~ collection of all the alleles in a population Allele Frequency ~ the number of times a specific allele appears in the gene pool Species-a group of interbreeding organisms that produce viable and fertile offspring in nature

Microevolution Microevolution is simply a change in gene frequency within a population. Evolution at this scale can be observed over short periods of time such as from one generation to the next. Example: The frequency of a gene for pesticide resistance in a population of crop pests increases quickly. Remind students that a gene is a sequence of DNA nucleotides that specify a particular polypeptide chain and that genes code for proteins. Have students generate an example for each of the 4 example “causes” of microevolution. Many correct answers are possible! natural selection favored the gene (sickle cell anemia & malaria) the population received new immigrants carrying the gene (light skinned population crosses with dark skinned population resulting in hybrids) some nonresistant genes mutated to the resistant version (natural immunities to disease among populations) because of random genetic drift from one generation to the next (founder effect)

Darwin’s Theory of Natural Selection Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those without those favorable traits. There are 4 parts to the theory of evolution by mean of natural selection

1. Genetic variation - members of a population often vary in their inherited traits

2. Overproduction - organisms produce more offspring than can survive - leads to competition

3. Struggle to survive - all organisms face constant struggle to survive due to limited resources

4. Survival of the fittest - Fitness refers to an organism’s ability to survive and reproduce in its environment - Individuals best adapted to environment have greater fitness - Over time, favorable traits increase in population, increasing the match between organisms and their environment

Relative Fitness There are animal species in which individuals, usually males, lock horns or otherwise compete through combat for mating privileges. Reproductive success is usually far more subtle! Relative fitness is defined as the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals. Emphasize to students that the phrases “survival of the fittest” and “struggle for existence” are commonly used to describe natural selection, BUT they should not be taken to mean between individuals! There are reproductive advantages among animals that are passive and do not involve a form of battle: An animal may be a better “food gatherer”, thus has more energy to lay more eggs. An animal may be better camouflaged, thus lives longer and produces more offspring.

Adaptations enhance an organism’s ability to survive and reproduce. Structural (body parts) Behavioral Physiological

Beneficial adaptations depend on environment Beneficial adaptations in one environment may be selected against survival in other environments

The Effect of Environmental Change Earth’s environment is ALWAYS changing and can cause a shift in selection pressures. As a consequence, traits or adaptations that were favorable may become unfavorable. Classic Example: The peppered moth Environmental changes often cause a shift in selection pressures. Traits that were once beneficial to a population of organisms may become detrimental and vice versa. http://www.techapps.net/interactives/pepperMoths.swf

The Peppered Moth & The Industrial Revolution The peppered moth, is native to England and exists in two forms, one is dark and the other light with a “peppered” appearance. Birds are its main predator. Prior to the industrial revolution, only 2% of the moths were dark. The industrial revolution produced vast amounts of sulfur dioxide and soot from the burning of coal which altered the environment. Environmental changes often cause a shift in selection pressures. Traits that were once beneficial to a population of organisms may become detrimental and vice versa. http://www.techapps.net/interactives/pepperMoths.swf

Figure it out with a partner!! Propose an explanation why fifty years after the start of the Industrial Revolution, 95% of the moths were dark. Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

Industrial Melanism England has since regulated the burning of coal and as a result, the trees are returning to their original state (A). Consequently, the coloring among the population of moths in Britain has shifted back so that the peppered moths are once again favored. Explanation: The trees were previously light and covered in lichens, thus peppered moths had the advantage of camouflage over dark moths. (You may have to point out the peppered moth near the top of photo A.) The SO2 gas produced from the industrial revolution killed the lichens. Furthermore, the soot produced during the burning of coal collected on tree trunks changing their appearance and darkening them. As a result, the darker moth is now more camouflaged and less likely to be eaten by birds.

Microevolution can occur in one of several ways: Immigrants into the population carrying new genes random natural events natural selection mutations Remind students that a gene is a sequence of DNA nucleotides that specify a particular polypeptide chain and that genes code for proteins. Have students generate an example for each of the 4 example “causes” of microevolution. Many correct answers are possible! natural selection favored the gene (sickle cell anemia & malaria) the population received new immigrants carrying the gene (light skinned population crosses with dark skinned population resulting in hybrids) some nonresistant genes mutated to the resistant version (natural immunities to disease among populations) because of random genetic drift from one generation to the next (founder effect)

Important Key Points Natural Selection acts on phenotype because differential reproduction and survival depend on physical characteristics not genotype. Although natural selection occurs through interactions between individual organisms and their environment, individuals do not evolve. Instead, populations evolve over time. Natural selection can only increase or decrease heritable traits that vary among individuals in a population Without variation, natural selection cannot occur Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

TWO Sources of Genetic Variation Mutations, any change in a DNA sequence, can provide new phenotypes, the raw material for evolution. Meiosis and sexual reproduction produce new recombinants of phenotypes upon which natural selection operates. Emphasize the importance of meiosis and sexual reproduction as the driving force of evolution. Meiosis is responsible new phenotypic combinations upon which natural selection can act. Meiosis recombines alleles in new combinations  which results in unique gametes due to the way chromosomes line up on the metaphase plate and crossing over.  Meiosis coupled with fertilization produces offspring with different combinations of alleles.  The genetic complement that the zygote receives will be different from either parent and  is different from any sibling.   Identical twins are genetically identical to one another but the likelihood that two siblings (not identical twins) will be genetically identical is extremely remote 223 x 223.  Tell students that the genetic “shuffling” during meiosis is like getting a new hand when playing cards. The wisteria pictured on the right has a mutation causing it to produce white flowers instead of purple flowers.

Mutations in General MOST mutations are recessive and deleterious (fatal). Mutations occurring in somatic (body) cells cannot be inherited and do not affect future generations. Only mutations occurring in gametes are heritable. Mutations can occur at either the gene or chromosomal level. Mutations may cause a sheep to have a 5th leg. But this is not evolution!  Emphasize that mutations lead to genetic variation. These next slides explain each of these mutation types. Students should have prior knowledge of genes, DNA, and mutations from Pre-AP Biology.

Point mutations occur when one nucleotide is substituted for another. Students should be aware of DNA, RNA, codons, amino acids and the mechanisms of protein synthesis. If it has been a year or two since their first biology course, you may have to refresh their memory. Also, it’s the synonyms (pun intended) that will confuse students—too bad we can’t decide on a single term to describe a single anomaly!

Genetic Code & Synonyms The genetic code contains “synonyms” for the coding of amino acids. For example the DNA codons GGA, GGG, GGT, GGC all code for the amino acid proline. This sort of mutation is called a synonymous or silent mutation.

C Called Synonymous because the substitution results in the same amino acid in the sequence. Called silent because the mutated protein is the same as the original protein

Nonsynonymous Point Mutations C Point mutations that do result in a different amino acid are called nonsynonymous or missense mutations. Emphasize that intermolecular force interactions between R groups establish the shape of a protein, thus establishing its function.

Nonsynonymous Point Mutations Missense mutations can affect the protein in one of THREE ways: (Remember the new amino acid will have a different R group on the protein) It can result in a protein that does not function as well as the original protein. (This happens most often.) It can result in a protein that functions better than the original protein. It can result in a protein that functions like the original protein. This is usually because the R groups are similar. Emphasize that intermolecular force interactions between R groups establish the shape of a protein, thus establishing its function.

Nonsynonymous Point Mutations Another type of nonsynonymous mutation is referred to as a nonsense mutation. In a nonsense mutation, the altered nucleotide sequence results in a premature stop codon which produces a truncated, incomplete and usually nonfunctional protein. Emphasize that intermolecular force interactions between R groups establish the shape of a protein, thus establishing its function.

Talk with a partner!! Explain the three types of point mutations. Use the following terms in your explanation: synonymous, silent, nonsynonymous, missense and nonsense Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

2) Frameshift Mutation A frameshift mutation occurs as a result of either an insertion or deletion of a nucleotide. This changes the amino acid sequence of the protein from that point forward. Almost all frame shift mutations are deleterious. Interesting example but emphasize that most frameshift mutations do not result in a functional protein.

2) Frameshift Mutation Example Recently, bacteria were found growing in a pool of nylon wastes. (Flavobacterium) These bacteria were actually digesting the nylon waste. Upon examining the genome of these bacteria, it was found there was a frameshift mutation in their DNA that caused the production of three different enzymes that could digest the nylon. Interesting example but emphasize that most frameshift mutations do not result in a functional protein.

3) Gene Duplication Any duplication of a region of DNA that contains a gene. Analogy: Evolution is more like editing a book rather than writing a book from scratch. Genes are duplicated and then moved; once duplicated genes are moved, they experience different mutations which can result in different proteins. As you might imagine, there can also be cutting and pasting or copying and pasting errors!

3) Gene Duplication Analogy: Evolution is more like editing a book rather than writing a book from scratch. Genes are duplicated and then moved; once duplicated genes are moved, they experience different mutations which can result in different proteins. As you might imagine, there can also be cutting and pasting or copying and pasting errors! Genes can also be duplicated and occasionally the duplication moves a gene from one chromosome to another. Each gene will accumulate different mutations altering the protein that is produced.

3) Gene Duplication Example Myoglobin is a protein that binds with oxygen in the muscles. This gene has been duplicated and modified many times. Many of the duplications are introns – noncoding segments of DNA. While some of the modified genes are exons which code for functional proteins. It has given rise to the hemoglobin gene. Analogy: Evolution is more like editing a book rather than writing a book from scratch. Genes are duplicated and then moved; once duplicated genes are moved, they experience different mutations which can result in different proteins. As you might imagine, there can also be cutting and pasting or copying and pasting errors!

Evolution of Hemoglobin Gene by Duplication Take some time to explain this slide and the evolution of hemoglobin genes. It drives home the point that genes are duplicated and experience different mutations.

Pseudogenes Pseudogenes are inheritable genetic elements that are similar to functional genes but are non-functional as they do not encode for proteins. Their biogenesis results from the duplication of a parental gene, or the transposition of an mRNA sequence into different place in the genome Pseudogenes can collect multiple mutations because they are not subject to natural selection….Why? Often referred to as “junk” DNA

Pseudogenes

4) Neutral Mutations Naturally evolving proteins gradually accumulate neutral mutations at a predictable rate. Neutral Mutations do not always affect the function of the protein and forms the basis for the molecular clock. EX: Cytochrome c, a small protein found on the mitochondrial membrane. Between mammals and reptiles there are 15 different amino acids or mutations. This is illustrating that there are some proteins that have been around for a “long time”. That being the case, over time, these proteins experience mutations that do not affect the function of a protein. For example both human and dog hemoglobin found in red blood cells carry oxygen, yet the two proteins vary only slightly in their amino acid sequencing. Cytochrome c is an example of this as well. The average rate of these mutations can be used as an evolutionary clock.

4) Neutral Mutations Mammals and reptiles diverged 265 million years ago. That means on average cytochrome c mutated every 17 million years. In comparing the evolution of other organisms and their cytochrome c one mutation every 17 million years holds true.

Changes in Cytochrome C Explain that a pseudogene is a gene that has been duplicated but certain mutations have rendered this gene nonfunctional so it is never transcribed or translated. It is part of the genome that is simply conserved. Above is a comparison ancestral cytochrome c and human cytochrome c. This gene has been highly conserved as it is a protein used in the electron transport chain of the mitochondria. Missense mutations occur more frequently in pseudogenes than in functional genes.

Talk with a partner!! Although cytochrome c is NOT a pseudogene, why would missense mutations occur more frequently in pseudogenes than in functional genes? Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question!

Cytochrome c Comparison A dash indicates that the amino acid is the same one found at that position in the human molecule. All the vertebrate cytochromes (the first four) start with glycine (Gly). The Drosophila, wheat, and yeast cytochromes have several amino acids that precede the sequence shown here (indicated by <<<). In every case, the heme group of the cytochrome is attached to Cys-14 and Cys-17 (human numbering). Assign the Amino Acid Sequences and Evolutionary Relationships activity as homework!

5) Chromosomal Rearrangement There have also been major changes in chromosome structure that result in changes within populations which can, in turn, result in the emergence of new species. These include: inversions deletions duplication translocations fusions Chromosomal rearrangement is another source of genetic variation.

a) Inversion Part of a chromosome breaks out and reinserts backwards.

b) Deletion Loss of all or part of a chromosome

c) Duplication Produce extra copies of parts of a chromosome.

d) Translocation Part of a chromosome breaks off & attaches to another chromosome

e) Fusion Entire chromosome attaches to another chromosome

5) Chromosomal Rearrangement Compare the karyotype of a human (H) and a chimpanzee (C). Notice the great apes have 24 pairs of chromosomes compared to 23 pairs of chromosomes in a human. Why the difference? Chromosome #2 in the human is the result of a fusion of two chimpanzee chromosomes. Chromosomal rearrangement is another source of genetic variation.

Human Impact on Gene Pools Ask students to give examples of artificial selection. They should come up with dog breeding, horse breeding, disease-resistant crops, etc. It is well documented that humans have had an impact on certain gene pools. For example, humans have selected for certain desirable traits within the mustard family and cultivated different agricultural products for human consumption. Called Artificial Selection

Artificial Selection When humans manipulate a gene pool it is called artificial selection. There are often consequences involved in such manipulations. For example in agriculture, farmers try to increase crop production, which may lead to many farmers growing only one variety of a particular crop such as corn. This leads to a loss of genetic diversity due to lack of variation within the population. If a disease attacks that particular variety of corn, the farmers growing that variety lose their entire crop. Emphasize the point that artificial selection can lead to the loss of genetic diversity. This has led to the creation of the Svalbard Global Seed Vault which on an island off of Norway. It is a place where seeds are kept and maintained to preserve genetic diversity.

Antibiotics and Artificial Selection When antibiotics are applied to a population of microorganisms to treat an infection, some of the microorganisms may be naturally immune to the drug. Why? A random mutation occurred in the genetic code of the microorganism conferring its resistance. These resistant microorganisms continue to flourish and cause disease, this is a classic example of natural selection.

Antibiotics and Artificial Selection The only remaining option a physician has is to treat the infection with a different antibiotic and hope that none of the surviving microorganisms possess a different random mutation that makes them resistant to the second antibiotic as well. The increase in antibiotic-resistant bacteria has caused doctors to reduce the number of prescriptions written for antibiotics in general. About 70% of pathogenic bacteria are resistant to at least one antibiotic and are called “super bugs” or MDR bacteria. (multidrug resistant) The mechanism pictured is that of penicillin. (note the artist’s use of the “P”s). It is illustrating how the drug attacks a bacterial pathogen. There are many related topics of discussion you can explore with students if time permits such as: Are we overusing antibiotics? Is it a good idea to let your immune system struggle for a few days at the first sign of a cold? If fever is our immune system’s first response to infection, what purpose is it serving?

Antibiotics and Artificial Selection Other examples are herbicide resistant weeds and insecticide resistant insects These can also be described as examples of artificial selection because of human influence in their evolution Video: What do we do when antibiotics don’t work anymore? https://www.ted.com/talks/maryn_mckenna_what_do_we_do_when_antibiotics_don_t_work_any_more?language=en#t-567304

MRSA or Methicillin-resistant Staphylococcus aureus MDR bacteria do not respond to “first line of defense” antibiotics. These types of bacteria are most commonly found in hospitals, on sports equipment and nail salons. Skin boils or similar lesions that do not heal often result. MDR bacteria can attack internal organs upon gaining entry into the body.

Reducing or Eliminating Gene Pools Human activities often cause random changes in gene pools and diminish gene flow for many species. This reduces genetic variation within a species. This impact is illustrated within populations of collared lizards (Crotaphytus collaris) living in the Missouri Ozarks. Forest fire suppression has reduced habitat and disrupted gene flow in this lizard Reduced genetic variation can lead to extinction Just interesting…Collared lizards in the wild have been the subject of a number of studies of sexual selection. In captivity if two males are placed in the same cage they will fight to the death. Males have a blue-green body with a light brown head. Females have a light brown head and body.

Learning Objectives Summaries

Really emphasize those last two bullets Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question! Use the image to explain the difference between allele frequency and gene pool.

Macroevolution Macroevolution is evolution on a scale of separated gene pools (not individuals). Think of it as an accumulation of modifications which result in speciation (forming a new species). Over long periods of time, steady input of new variations in a population lead to speciation. Macroevolution will be dealt with separately and the definition of macroevolution varies by textbook. -it can explain the evolution of more complicated things like the how the eye evolved -it can explain how speciation occurs -it can explain how populations on a broader scale evolve

Effect of Sexual Reproduction Sexual reproduction recombines genes in new ways. This results in unique offspring that differ from either parent or sibling. Humans make 223 different kinds of gametes. Fertilization means that the uniqueness of an individual is 223  223. Or the probability that two siblings will be genetically identical (excluding identical twins) is 446. Ask students “Why TWO to the 23rd?” First, they should know that humans have 46 chromosomes which can be arranged into 23 pairs with the “last” pair being XX if female and XY if male. Since gametes are haploid, they have only 23 chromosomes. We use 2 because there are 2 chromosomes in a pair, and you have 23 pairs. In order to figure out the probability you raise 2 to the 23rd power, which gives you 8.3 million different possibilities for only the egg or sperm. So, if you take 8.3 million times 8.3 million, you get 64 trillion different possibilities for fertilization, without even considering crossing over. That’s a lot of unique phenotypes upon which natural selection can act! Sexual reproduction is like shuffling a deck of cards and every time getting a new and unique hand dealt. It is the major driving force of evolution.

Figure it out with a partner!! Really emphasize those last two bullets! When students write about evolution it is VERY important that they can “say what they mean and mean what they say”. These last two bullets belong in the response to any evolution free-response question! Use the image to explain the difference between allele frequency and gene pool.

Hemoglobin Comparison This is a comparison between the differences in the amino acid sequence of human hemoglobin and different species. The last three species do not have a distinction between a and b chains. There is an inverse relationship between the difference in the amino acid sequence and how closely related the organisms are to humans. The b chain of hemoglobin has 146 amino acids. Ask the students to speculate as to why soybeans might have a protein similar to hemoglobin. Leghemoglobin removes oxygen that would kill a bacteria living in the root of the soybean. This bacterium “fixes” nitrogen in the roots of the soybean or takes nitrogen from the air and changes it into a usable form that the plant can use.

Hemoglobin Comparison A nice visual representation of the biochemical differences.

Created by: Carol Leibl Science Content Director National Math and Science