Solved by a verified expert:1. Shown
below is a 220 base pair segment of a bacterial DNA. The sequences of both
strands of the DNA duplex are shown here. The top strand reads 5′ to 3′; the
bottom complimentary strand reads 3′ to 5′ left to right.
i)
Open up the first 60 bases as a replication fork. Show the primer location and
their polarities for the leading and lagging strands.
ii)
As you know, DNA synthesis requires a primer, which is synthesized by a
primase. Suppose you want to replicate the DNA in this replication fork, what would
be the 5’ to 3’ sequence of a primer (write 10 bases) and its polarity for the
top and the bottom strands.
2.
The following diagram shows a replicating region of a human chromosome. Regions
being replicated appear as bubbles. Newly synthesized strands are not shown in
the figure. A) Assuming bidirectional replication, how many origins of
replication are active in this DNA molecule? B) How many replication forks are
present in this diagram? C) Assuming that all replication forks move at the
same speed, which origin of replication was activated last?
3.
You have done a cross between two strains of yeast, one strain has the genotype
A B C and the other strain has the a b c genotype, where the letters refer to
three rather closely linked genes in the order given. You analyzed many tetrads
resulting from this cross, and you find two tetrads that do not contain the
expected two B and two b spores. In tetrad I, the spores are A B C, A B C, a B
c, and a b c. In tetrad II, the spores are A B C, A b c, a b C, and a b c.
Explain how these unusual tetrads could have been produced?
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