1.E: Overview, DNA, and Genes (Exercises)
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These are homework exercises to accompany Nickle and Barrette-Ng's "Online Open Genetics" TextMap. Genetics is the scientific study of heredity and the variation of inherited characteristics. It includes the study of genes, themselves, how they function, interact, and produce the visible and measurable characteristics we see in individuals and populations of species as they change from one generation to the next, over time, and in different environments.
1.1 How would the results of the cross in Figure 1.11 have been different if heredity worked through blending inheritance rather than particulate inheritance?
1.2 Imagine that astronauts provide you with living samples of multicellular organisms discovered on another planet. These organisms reproduce with a short generation time, but nothing else is known about their genetics.
a) How could you define laws of heredity for these organisms?
b) How could you determine what molecules within these organisms contained genetic information?
c) Would the mechanisms of genetic inheritance likely be similar for all organisms from this planet?
d) Would the mechanisms of genetic inheritance likely be similar to organisms from earth?
1.3 It is relatively easy to extract DNA and protein from cells; biochemists had been doing this since at least the 1800’s. Why then did Hershey and Chase need to use radioactivity to label DNA and proteins in their experiments?
1.4 Compare Watson and Crick’s discovery with Avery, MacLeod and McCarty’s discovery.
a) What did each discover, and what was the impact of these discoveries on biology?
b) How did Watson and Crick’s approach generally differ from Avery, MacLeod and McCarty’s?
c) Briefly research Rosalind Franklin on the internet. Why is her contribution to the structure of DNA controversial?
1.5 Starting with mice and R and S strains of S. pneumoniae, what experiments in additional to those shown in Figure 1.3 to demonstrate that DNA is the genetic material?
1.6 List the information that Watson and Crick used to deduce the structure of DNA.
1.7 Refer to Watson and Crick’
a) List the defining characteristics of the structure of a DNA molecule.
b) Which of these characteristics are most important to replication?
c) Which characteristics are most important to the Central Dogma?
1.8 Compare Figure 1.13 and Table 1.1. Which of the mutants (#1, #2, #3) shown in Figure 1.13 matches each of the phenotypes expected for mutations in genes A, B,C?
1.9 Refer to Table 1.2
a) What is the relationship between DNA content of a genome, number of genes, gene density, and chromosome number?
b) What feature of genomes explains the c-value paradox?
c) Do any of the numbers in Table 1.2 show a correlation with organismal complexity?
1.10 a) List the characteristics of an ideal model organism.
b) Which model organism can be used most efficiently to identify genes related to:
i) eye development
ii) skeletal development
iii) cell division
iv) cell differentiation
1.11 Refer to Figure 1.8
a) Identify the part of the DNA molecule that would be radioactively labeled in the manner used by Hershey & Chase
b) DNA helices that are rich in G-C base pairs are harder to separate (e.g. by heating) than A-T rich helices. Why?