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U-M BIOLOGY 171 - Exam 2 Study Guide
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BIO 171 1st EditionExam # 2 Study Guide Lectures: 7 - 12Lecture 7 (February 4)How can phenotypic ratios be modified b interactions between genes? Give an example of this. Phenotypic ratios can be modified by interactions between genes that modify the phenotypic expression of other genes. These genes are said to express epistasis. An example of epistasis is blood type, where the gene that codes for a functional or non-functional protein will affect the gene for which blood type you have because not having the functional protein automatically codes for type O blood. Are X linked mutations more commonly expressed in males or females? Why? X linked mutations are more commonly expressed in males because males only posses one X-chromosome while females have two. If the mutation happens to be on the male’s X chromosome it will automatically be expressed, where as females would need both of their X chromosomes to carry the mutation. What is independent assortment? How does it effect recombination? Independent assortment is the idea that each pair of alleles segregates independently of other alleles during gamete formation. This effects recombination because during the process of recombination, alleles “cross over” to form a different combination of alleles in the offspring than in the parents. Lecture 8 (February 9) What is the difference between homology and analogy in organisms? List examples of both. Homologies are similarities in organisms due to common descendant from a shared ancestor; analogies are similarities in organisms that result from convergent evolution (result of adaptation to their environment). An example of homology is the development of front limbs orback limbs, and an example of an analogy is the fact that both bats and birds posses wings, but each species uses their wings differently as a result of their different environments and environmental needs. What are the conditions needed for natural selection to occur?First, there must be variation within the population because something needs to be “selected” or favored; also, there must be a selective pressure that favors one variation over the others (ex= a predator); Lastly, biological evolution must occur within the population meaning the proportion of favored alleles must increase. Name two different things we can observe from a phylogenetic tree. How are they represented?What do they tell us? From a phylogenetic tree we can observe monophyletic groups, or groups that include a common ancestor and all of its descendants. These groups are represented by all of the branches and nodes that include these descendants, and they allow us to reflect evolutionary relationships in the best way because they include all the descendants of a certain group. Another thing we can observe from a phylogenetic tree is speciation events, which are represented by nodes, and allow us to see when new species formed throughout history. What are shared derived traits? Why are they so important in constructing phylogenies? Shared derived traits are traits that are found in all members of a phylogeny besides the outgroup. They are most useful in constructing phylogenies because they allow us to see the differences between species. Lecture 9 (February 11)What is the difference between discrete and polygenic traits? List examples of each. Discrete traits are traits whose phenotypes fall into a few distinct classes. For example, purple or white flowers. Polygenic traits display a normal distribution, and two or more genes affect the phenotypes of these traits. An example of a polygenic trait is human height because there are many possibilities for height, not only “tall” and “short”.What is an example of a genotype-by-environment interaction? A genotype-by-environment interaction is when a phenotype is the result of an interplay between genotype and the environment. There are many examples of this, but one example is emphysema because acquiring emphysema is a result of carrying the gene for the disease as well as coming into contact with environmental factors that can cause it, like smoking cigarettes.How are SNPs (single-nucleotide polymorphisms) useful in genetic mapping? They are useful because they allow geneticists to identify what gene is responsible for carrying acertain trait. By comparing the genotypes, and the single base variations within the genomes (that are found in more than 1% of the population), they can identify which nucleotides code forwhat.Name the three types of selection. How does each of them affect the population mean? With each, does genetic diversity increase or decrease?One type of selection is stabilizing selection, which favors individuals that have intermediate phenotypes. For this type of selection, the population mean stays the same, and the amount of genetic variation decreases (extremes are lost). The next type of selection is directional selection, which favors one allele. In this selection, the population mean changes (depending onwhich allele is favored), and genetic diversity decreases because some alleles become fixed while others are lost. The last type of selection is disruptive selection, which favors the extreme phenotypes in a population. This type of selection does not significantly change the population mean, and maintains or increases genetic variation because both extremes are favored. Lecture 10 (February 16)What is anisogamy? Why does it have such a big influence on sexual selection? Anisogamy means that gametes in different sexes are different sizes. Males make many, small gametes while females make few, large gametes. This affects sexual selection because it causes the females to be choosier about their mates. They have fewer eggs, and provide more resources (time, energy, etc.) per egg so they must choose carefully about who they reproduce with. What are the two forms of sexual selection? What are the differences between them?The two main forms of sexual selection are intrasexual selection and intersexual selection. Intrasexual selection is competition within a sex (usually males) for a mate, and intersexual selection is between the sexes (female choice)In a species of bird called the red-crested manakin of Ecuador, males perform a dance to court females that resembles the “moon walk”. Females closely watch the male’s performance and mate with the best dancers. Intersexual selection could account for the male’s elaborate courtship


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U-M BIOLOGY 171 - Exam 2 Study Guide

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