In this problem we will explore some of the many ways that mutations in two different genes can interact to produce different Mendelian ratios. Consider a hypothetical insect species that has red eyes. Imagine mutations in two different unlinked genes that can, in certain combinations, block the formation of red eye pigment yielding mutants with white eyes. In principle, there are two different possible arrangements for two biochemical steps responsible for the formation of red eye pigment. The two genes might act in series such that a mutation in either gene would block the formation of red pigment. Alternatively, the two genes could act in parallel such that mutations in both genes would be required to block the formation of red pigment.

Further complexity arises from the possibility that mutations in either gene that lead to a block in enzymatic activity could be either dominant or recessive. If the crosses is made between a wild type insect with red eyes and a true breeding white eyed strain with mutations in both genes. Such considerations yield the Pathways in parallel with recessive mutations in both genes, determine the phenotype of the F1 progeny and the expected phenotypic ratio of red to white eyed insects in the F2.

#Question id: 3828

#Unit 3. Fundamental Processes

Why does E. coli need both DNA polymerase III and DNA polymerase I?

#Question id: 3829

#Unit 3. Fundamental Processes

Why is only one copy of DNA made per cell division cycle in eukaryotes despite the presence of multiple origins of replication?

#Question id: 3830

#Unit 3. Fundamental Processes

Why is DNA damage in skin cells from exposure to excessive UV light not completely reversed by photoreactivation?

#Question id: 3831

#Unit 3. Fundamental Processes

State whether the following statements is true/false regarding DNA replication.

1. In E. coli replication begins at the origin of replication and proceeds in one direction until the entire circular DNA molecule has been copied.

2. The chromosome of the fruit fly (D. melanogaster) is about twice as large as the E. coli chromosome.

3. Prokaryotic DNA replication occurs in two steps. First, ATP provides a phosphate to the growing DNA chain. This is followed by addition of a nucleoside.

4. DNA polymerase III is the largest DNA polymerase in E. coli.

5. The β subunits of E. coli DNA polymerase form a sliding clamp that surrounds the DNA strands at the replication fork.

#Question id: 3832

#Unit 3. Fundamental Processes

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). Which two classes of DNA do these different samples represent?

#Question id: 3833

#Unit 3. Fundamental Processes

Regarding DNA replication, which, if any, of the following statements is incorrect?