Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
In the following drawing, the top strand is the template DNA, and
the bottom strand shows the lagging strand prior to the action of
DNA polymerase I. The lagging strand contains three Okazaki
fragments. The RNA primers, which are shown in red, have not yet
been removed.
A. Which Okazaki fragment was made first, the one on the left or
the one on the right?
B. Which RNA primer will be the first one to be removed by DNA
polymerase I, the primer on the left or the primer on the right?
For this primer to be removed by DNA polymerase I and for the
gap to be filled in, is it necessary for the Okazaki fragment in
the middle to have already been synthesized? Explain.
C. Let’s consider how DNA ligase connects the left Okazaki fragment
with the middle Okazaki fragment. After DNA polymerase I
removes the middle RNA primer and fills in the gap with DNA,
where does DNA ligase function? See the arrows on either side
of the middle RNA primer. Is ligase needed at the left arrow, at
the right arrow, or both?
D. When connecting two Okazaki fragments, DNA ligase needs to
use ATP as a source of energy to catalyze this reaction. Explain
why DNA ligase needs another source of energy to connect two
nucleotides, but DNA polymerase needs nothing more than the
incoming
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