Evolution Unit 5 Overview

Sexual Selection---After watching the video, “Why Sex?” Discuss and then answer the following questions:

What are the advantages and disadvantages of asexual and sexual reproduction?

Sexual Reproduction

Advantage Disadvantage

Asexual Reproduction

Advantage Disadvantage

What is the trade-off (pro’s and con’s) of having a phenotypic (appearance) adaptation that helps you evade predators versus a phenotypic (appearance) adaptation that helps you attract a mate. Which is more important—why?

LT #4 Evolutionary Forces 1 "In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny1 of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism2 to snails, bees, giraffes, and dandelions." Douglas J. Futuyma in Evolutionary Biology What changes in evolution? Actually what changes is the frequency of an allele. The frequency of an allele in the gene pool of a population is how often an allele occurs in the genotypes of individuals of the same species that are in the same area - the same population. How often the allele occurs depends on lots of factors such as 1) what the allele codes for - is it a critical trait for survival and 2) is the allele a dominant or a recessive allele. These factors determine whether the allele will be present for a long time or a short time. Natural selection acts on population by changing the frequency of different alleles. If an allele is harmful, it will be eliminated from the population or reduced in its frequency because those individuals in the population exhibiting the trait will not survive. This leads to a fine difference between genotype and phenotype. Remember genotype is the kinds of genes an individual has and phenotype is its observable traits. It is the observable traits that are selected for or against resulting in increased allele frequency or reduced allele frequency, respectively. Since we are also considering genotypes, recall that the three ways that mutations happen most often are changes in the DNA (deoxyribonucleic acid) sequence due to insertions, deletions, or substitutions. Evolution can be thought of as an accumulation of changes that occur within a population resulting from genetic and environmental changes. Within a population of organisms of the same species there are differences between the individuals (variation). A species is a group of individuals that can interbreed and produce fertile offspring (offspring that can reproduce). The greater the variation between individuals the greater the likelihood that the species will survive if the environment changes. Since the Earth was created, many environmental changes have occurred and some species have become extinct and others have apparently changed into different species. If an environment

1 Ontogeny: the development of an individual from the moment the egg is fertilized up till adulthood. 2 Protoorganisms: bacteria. LT #4 Evolutionary Forces 2 changes too much and there is not enough variation within the population, few if any individuals will survive the change, resulting in the species becoming extinct. But if there is sufficient variation so that some “weirdoes” can survive, then those will be the ones that can reproduce and their characteristic genes transmitted to the next generation. If there were a few before the change, then after the change they will be the majority apparently evolving into another species. Looking at fossils (mineralized remains of organisms) similarities can be observed. Paleontologists and evolutionary biologists have developed relationships between existing and extinct species by tracing anatomical and genetic similarities and differences.

Besides mutations and large scale environmental changes, more minor changes can result in speciation. Speciation is the formation of a new species or group of organisms that can no longer interbreed with an original species population. These organisms no longer interbreed because their characteristics (either biological or behavioral) have become too different. This can happen randomly and by geographic isolation of a species. A random change in the kinds of genes in a population is called genetic drift. When populations of interbreeding individuals of the same species are large, the the allele frequency of each successive population is expected to vary little from the frequency of its parent population unless there are adaptive advantages associated with the alleles. But with a small breeding population (a group separated by geography), a change in even one individual can cause a disproportionately greater change in the population’s gene pool. Therefore small populations are more subject to genetic drift effects than large populations. A situation exists when large populations are quickly reduced. This population reduction is called a population bottleneck. Like a bottleneck that is narrower than the bottle genetic variation is reduced. The reduced variation results in sudden changes in the allele frequency within the gene pool, and of the population’s characteristics. These type of changes are not gradual and called punctuated because sudden and drastic changes can occur. So evolutionary changes are not always slow (gradualism) or always rapid (punctuated equilibrium). Vocabulary

1. Evolutionary Fitness ______

______

2. Founder effect______

3. Gene Pool ______

4. Genetic Drift______

5. Natural selection ______

6. Phenotype ______

7. Population______

LT #4 Evolutionary Forces 3 ______Evolution Unit Study Guide A population of land snails colonized a field of yellow grass. At first, the population contained two types of snails, one with brown bands on their shells and another with yellow bands on their shells, as shown in the figure below. After 10 years, most of the snails had shells with yellow bands.

1. Why was the yellow-banded snails favored in this environment?

2. What specific abiotic or biotic part of the environment favored the yellow-banded snails?

A field of crops was sprayed with pesticides to control a population of insects that was eating the crop. Only 1% of the insects survived. The same amount and type of pesticide was sprayed on the field each year for the next 4 years. The graph below shows the percentage of insects that survived each year after the pesticide was used.

3. Why was the pesticide less effective each year in its ability to control the target population of insects?

4. According to Darwin’s theory of natural selection, individuals who survive are the ones best adapted for their environment. What does this mean exactly

______

LT #4 Evolutionary Forces 4 5. When mountain lions prey on a herd of deer, some deer are killed and some escape. Which part of Darwin’s concept of natural selection might be used to describe this situation?

6. A change in a sequence of DNA is called a

7. If a mutation introduces a new skin color in a lizard population, what factor might determine whether the frequency of the new allele will increase? ______

8. The difference in the fur color of the individual species in a population is described as ______

9. Genetic drift is most likely caused by

10. Describe a gene pool.

11. What is your gene pool as a human being? ______

12. Individuals within a population of rabbits have different colors of fur as shown in the diagram below. The difference in the fur color of the individual rabbits is described as ______.

13. What are the five factors that influence evolution within a population?

LT #4 Evolutionary Forces 5 14. If height is a phenotypic trait, that is determined by one gene and there are two alleles, one for tall and one for short, tall being dominant over short, the genotype of a tall individual can be TT (Homozygous Dominant) or Tt (Heterozygous) and the genotype of a short individual is tt (Homozygous Recessive).

Based on your previous knowledge, notes and context of the paragraph above—what do you think it means by:

Phenotype: Allele:

Genotype: Homozygous Dominant:

Heterozygous: Homozygous Recessive:

15. You have been asked to see if the population of humans in Oregon is undergoing an evolutionary shift in height. You knew that in 1990, the allelic frequency for the Tall gene (T) was 35% and the allelic frequency for the Short gene (t) was 65% percent.

You have just collected the data for the current population in 2011, you determine that 25% of the population is short. So you begin to calculate the Hardy-Weinberg Equation to see if evolution has taken place.

You know that if you have short people, it is recessive. They had to inherit 2 short genes from their parents. Therefore for short people:

Phenotype: Short Genotype: tt (homozygous recessive) q2 = frequency of homozygous recessive individuals (tt) and we know that is 25% from above.

To determine q, which is allelic frequency of (t) all we have to do is simplify the following equation:

2 √q = √.25, to simplify to q = √.25, which simplifies to q = .5

To determine p, which is the allelic frequency of (T) we have to use the following equation p + q = 1

P + .5 = 1, to solve for p, p = .5

To determine how many tall people that do not carry a short gene, use p2, .52 = .25 (homozygous dominant) (TT)

To determine how many tall people that carry a short gene, use 2pq = 2(.5)(.5) = .50 (heterozygous) (Tt)

Is there evolutionary pressure on the height gene in Oregon? Propose a reason—based on the 5 influences.

LT #4 Evolutionary Forces 6