Question 20.41

The genome of Drosophila melanogaster, a fruit fly, was sequenced in 2000. However, this “completed” sequence did not include most heterochromatin regions. The heterochromatin was not sequenced until 2007 (R. A. Hoskins et al. 2007. Science 316:1625–1628). Most completed genome sequences do not include heterochromatin. Why is heterochromatin usually not sequenced in genomic projects? (Hint: See Chapter 11 for a more detailed discussion of heterochromatin.)

Question 20.42

In metagenomic studies, a comparison of ribosomal RNA sequences is often used to determine the number of different species present. What are some characteristics of ribosomal sequences that make them useful for determining what species are present?

Question 20.43

Some synthetic biologists have proposed creating an entirely new, free-living organism with a minimal genome, the smallest set of genes that allows for replication of the organism in a particular environment. This genome could be used to design and create, from “scratch,” novel organisms that might perform specific tasks such as the breakdown of toxic materials in the environment.

• a. How might the minimal genome required for life be determined?
• b. What, if any, social and ethical concerns might be associated with the construction of an entirely new organism with a minimal genome?