


Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
Material Type: Lab; Class: General Biology II; Subject: Biology; University: Central Oregon Community College; Term: Unknown 1989;
Typology: Lab Reports
1 / 4
This page cannot be seen from the preview
Don't miss anything!
Identify the mechanisms that produce change in allele frequencies. Test hypotheses about allele frequencies using simulations Draw conclusions about how effective different evolutionary mechanisms can be. You, as an individual, have a whole set of genes , your genome, which are segments of the DNA molecules we call chromosomes. The genes code for building and maintaining you as a living creature. Can you (or any individual) evolve in the biological sense? In other words, will your alleles, the different versions of a particular gene, change over your lifetime? You share genes with other humans and it is possible to determine allele frequencies for a population, members of a species that share a particular area at a specified time. The sum total of these genes in a population is called the gene pool. Population membership changes over time. Think of some ways in which this could happen. If population membership changes, would you expect that, under certain conditions, allele frequencies in this population could change over time as well? This is the topic of today’s lab—how allele frequencies can change over time or the mechanisms of evolution. If allele frequencies are significantly changing over time, the population has evolved. To observe evolution, we would need to look at several generations (perhaps 100’s or 1000’s) of a population. This would be difficult to achieve in a three-hour laboratory. Even bacteria need approximately a half-hour to reproduce! Instead, you will use simulations (simplified models of the real thing) to determine if and how evolution of population occurs. The primary goal of this lab is to give you insight about how evolution can and does work. Review of Mendelian Genetics It is important to distinguish an individual’s appearance, or phenotype , from the alleles present in that individual’s cells. Every individual carries two alleles of a given gene; the description of these alleles is a genotype. Recessive alleles are those that are masked or hidden by another allele. For example, the allele for blue eye color ( recessive ) is masked by an allele for a pigment such as brown. Pigment is thus dominant over blue. By convention, recessive alleles are denoted be lowercase letters and dominant alleles by uppercase letters. If “P” stands for pigment and “p” stands for nonpigmented eye color, then blue-eyed individuals have the genotype “pp” since they have two recessive alleles, while individuals with pigmented eyes are either “Pp” or “PP”. We cannot identify the correct genotype for the pigmented phenotype unless we gain more information about parents and/or offspring, since it takes only one dominant allele to mask a recessive allele. Note that some genotypes involve identical pairs (“pp” and “PP”, called homozygous (alike) and some involve a mixed pair (“Pp”, called heterozygous ). Most human traits, such as facial features, height, dexterity, etc. are controlled by numerous alleles, and many of these have complex interactions among themselves and with the environment. These traits can be very difficult to study. Some human physical and biochemical traits are controlled through the inheritance of single genes with two or more alternate alleles, for example traits such as blood type. We will examine eight such traits in this class.
non-dimpled chin
attached earlobes
straight hairline
nontaster
Right thumb on top
finger not bent
Hitchhiker’s thumb
nonroller
To determine if a population is evolving it is necessary to keep track of allele frequencies in the population over time. Alleles, for sexually reproducing organisms, of course, are inherited as a pair, each associated with a homologous chromosome. One allele is inherited from the father (via sperm) and the other from the mother (via the ovum or egg). Therefore, each individual in the population will contribute two alleles. To simplify things, you will only consider two versions of a gene. Let’s say we have a dominant allele, A , and a recessive allele, a. We need to know the frequency of each in the initial population so that it is possible to track any changes in frequency over time. Let’s say the frequency of A is represented by the letter p. And q represents the frequency of a. Because, for this example, there are only A’s and a’s in the population and the sum of all frequencies should equal 100% (or 1.00), then what is the relationship of p and q to the total frequency of alleles in the population? Write the equation showing the relationship between the total frequency (i.e. 1.00) and the frequencies (p and q) of A and a in the population (see Question 1 on the lab assignment sheet to turn in).
Repeat this procedure again using only the beans in the new cup, then adjust the number of red and white beans in the cup based on your results. Continue to draw new population combinations until you have data for ten generations or have only one color of bean left. Record your genotype and allele frequencies for the tenth generation on the board.
The problem with the bean simulations is they can take up time to model even a few generations. Now we will model microevolutionary mechanisms, but using a computer program instead of beans. By using the computer, it is possible to collect simulated data over 100’s of generations rather than only a few. The computer program we will be using is called Ecobeaker. The chapter beginning on page L-155 in the Software guide entitled “Islands and Natural Selection” is the one that we will use for this computer simulation. After the instructor gives you an introduction to the program, follow the instructions below to conduct the models.
Change the following parameters: Best beak length: 10 Length selection coefficient: 0. Carrying capacity: 500 Num beak length loci: 10 Now run the simulation for 300 generations and then answer question 9. Now tinker with the selection coefficient by changing its values (can range from 0-1). Remember to repeat each simulation five times to determine a pattern.