Dna/rna Genetics Worksheet With Answers printable pdf download

1. The base composition of a virus was found to be 11% A, 32% G, 18% U and 39% C.

It this a DNA or RNA virus? Is it single-stranded or double-stranded?

The presence of Uracil shows that it is RNA. The base composition is unequal, so it must

be single stranded.

2. Which of these DNA fragments will have a higher melting temperature? (circle one)

A) GCATTGACCGGAGGGACT

B) GGATTTCAATTACTTAAT

CGTAACTGGCCTCCCTGA

CCTAAAGTTAATGAATTA

A has a higher melting temperature. The triple hydrogen bonds between G and C are

harder to break, so fragments with higher GC content will have a higher melting

temperature.

3. Here is a very short chromosome of a eukaryotic cell that lacks telomerase.

Replication starts near x. One strand of the DNA has been labeled with heavy (15) N,

hence the capital letters, but all newly synthesized DNA will have normal N.

5’ aaaggg . . . . . . . . x . . . . . . . ccctttggg 3’

3’ TTTCCC . . . . . . . . X . . . . . . . GGGAAACCC 5’

That cell divides to make two daughters, which in turn divide to make two granddaughter

cells.

Draw the cell pedigree, showing this chromosome in the two daughter and four

granddaughter cells. (For the purposes of this question, assume that replication uses a

primer that is only 3 bases long. Also, real chromosomes would have specific sequences

at the ends- I just used these because they are easy to write down.)

This question required you to put together two different concepts: semi-conservative

replication and the function of telomerase.

Semi-conservative replication

means

that heavy N would be present in only one of the

four granddaughter chromosomes.

The lack of telomerase meant that the new strands would be shorter at the 5’ end each

generation, leaving a 3’ overhang. Because it is semi-conservative, the original strand is

unchanged, however. So at the end you have a mix of short and long strands.

Assuming the primer is 3 bases long, the chromosomes will get shorter in multiples of 3.

Daughters

5’ aaaggg . . . . . . . . x . . . . . . . ccctttggg 3’

3’ tttccc . . . . . . . . x . . . . . . . gggaaa

5’

ggg . . . . . . . . x . . . . . . . ccctttggg 3’

3’ TTTCCC . . . . . . . . X . . . . . . . GGGAAACCC 5’

Dna/rna Genetics Worksheet With Answers