Heritable Variation, the Raw Material of Evolution: Chapter 5 Study Guide Questions Evolution can only take place if there is variation between individuals to begin with. The genetic material, DNA, is the ultimate source of the variation that evolution acts upon. Charles Darwin is thought of by many as being the first to discover evolution. You should understand by now that this is not a very good description of his contributions to our understanding of evolution, but he did establish some very important ideas, most especially the principle of natural selection. In his lifetime he measured variation among members of the same species but did not know what the source of the variation was. You have more knowledge of this than Charles Darwin did. Knowing what you know about variation between individuals, consider the sources of variation that might contribute to characteristics that distinguish individuals from each other within a species. This chapter begins with a brief examination of the variation in height among humans. For each characteristic that shows evidence of variation among humans (height, weight, hair color, running speed, reading comprehension ability, cancer risk) ask yourself whether this character is influenced mainly by genetics (DNA sequences), the environment (essentially everything that isn’t DNA), or a combination of both. If a genetic component is involved, is it likely to be a simple genetic trait (only one gene controls the trait) or a complex trait (many genes contribute to the phenotype, along with environmental contributions)? Unfortunately for you, this chapter includes a summary of molecular genetics in the form of what I call an “infodump”. This is meant to be a review for people who are already very familiar with the Central Dogma of molecular biology. Review some of these concepts to be sure you can answer the following questions: What is the ultimate purpose of gene expression? What are genes made of and what are they for? How does information in DNA result in the formation of proteins? What is messenger RNA and how is it used in the cell? How can mutations to a DNA sequence affect the shape of a protein? Can mutations cause any effect on gene expression without changing the shape of a protein? How does a transcription factor affect gene expression? What controls the action of transcription factors? (Think of the signals that result in changes to gene expression) What role do introns and exons play in gene expression? What are the major differences in gene expression between prokaryotes and eukaryotes? How do the genomes of eukaryotes and prokaryotes differ? Mutations can arise from more than just a single base pair change. What other ways can changes to the genome alter gene expression? What kind of mutations affect more than one gene? A cis-element is a DNA sequence that is part of the same gene. It is easy to see how a change in the sequence of a gene affects that gene’s protein product. But how does a trans-acting mutation work? Which kind of mutation is more important for evolution, a somatic mutation or a germline mutation? Why? How many alleles of each gene are present in a human brain cell? A human egg cell? A human sperm cell? A bacterial cell? Considering what you know about the different parts of a gene, how could a mutation to the regulatory region of a gene result in a dominant or a recessive mutation. Think about how the amount of a protein changes, or where or when it is expressed. How might a mutation in the coding region of a gene result in a dominant or recessive mutation? Think about what the protein is actually doing. Mendel established the principle of independent assortment but knew nothing about chromosomes. How is the sorting of chromosomes during meiosis and fertilization related to the principle of independent assortment and expression of alleles? The traits that Mendel studied were all simple genetic traits. Are there any simple genetic traits in humans? What makes a complex trait (or quantitative trait) different from a simple trait? Gene expression can be at least partially dependent on environment. In this context, what is the “environment”?
