Question

The relative percentages of nitrogenous bases of the genetic material isolated from various species (P, Q, R, S and T) are listed in the following table.

Species	Adenine	Guanine	Thymine	Cytosine	Uracil
P	$21$	$29$	$21$	$29$	$0$
Q	$29$	$21$	$29$	$21$	$0$
R	$21$	$21$	$29$	$29$	$0$
S	$21$	$29$	$0$	$29$	$21$
T	$21$	$29$	$0$	$21$	$29$

Choose the correct statement from the following.

• A. Species P, Q and R contain single-stranded DNA; S and T cannot contain double-stranded RNA
• B. Species P, Q and R contain double-stranded RNA; species S and T contain single-stranded RNA
• C. Species P, Q and R cannot contain single-stranded DNA; species S contains single-stranded RNA; species T contains double-stranded RNA
• D. Species P and Q contain double-stranded DNA; species R contains single-stranded DNA; species S contains double-stranded RNA; species T contains single-stranded RNA

Answer 1

The correct option is D Species P and Q contain double-stranded DNA; species R contains single-stranded DNA; species S contains double-stranded RNA; species T contains single-stranded RNA

DNA has base pairs adenine, thymine, guanine and cytosine. RNA has base pairs adenine, guanine, cytosine and uracil. In a double stranded DNA, number of adenine will always be equal to number of thymine and number of cytosine will always be equal to number of guanine as per Chargaff's rule. In species P, number of adenine are equal to number of thymine. Also, it has same number of guanine and cytosine. It does not have uracil in its genome. Hence, species P is double-stranded DNA. Similarly, species Q is double-stranded DNA. Species S has uracil instead of thymine in equal number as adenine. Also, number of guanine are equal to cytosine. Hence, species S is double-stranded RNA. T has uracil in its genome. Also, number of adenine are not equal to uracil and number of guanine are not equal to cytosine. Hence, species T is single-stranded RNA.

Thus, the correct answer is option D.