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In a single organism, what do you notice about the relative proportions of DNA bases?

A. [tex]$A$[/tex] and [tex]$T$[/tex] occur in similar proportions.
B. T and G occur in similar proportions.
C. [tex]$A$[/tex] and [tex]$C$[/tex] occur in similar proportions.
D. G and C occur in similar proportions.

\begin{tabular}{|c|c|c|c|c|}
\hline \multicolumn{5}{|c|}{Relative Proportions (\%) of Bases in DNA} \\
\hline Organism & A & T & G & C \\
\hline Human & 30.9 & 29.4 & 19.9 & 19.8 \\
\hline Chicken & 28.8 & 29.2 & 20.5 & 21.5 \\
\hline Grasshopper & 29.3 & 29.3 & 20.5 & 20.7 \\
\hline Sea urchin & 32.8 & 32.1 & 17.7 & 17.3 \\
\hline Wheat & 27.3 & 27.1 & 22.7 & 22.8 \\
\hline Yeast & 31.3 & 32.9 & 18.7 & 17.1 \\
\hline E. coli & 24.7 & 23.6 & 26.0 & 25.7 \\
\hline
\end{tabular}

Sagot :

To determine what happens within a single organism regarding the relative proportions of DNA bases, we can evaluate the given data on a case-by-case basis for each of the organisms listed in the table.

The DNA bases in question are Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). According to the base pairing rules established by Chargaff’s rules, Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). Hence, in a double-stranded DNA, the amount of A should be roughly equal to the amount of T, and the amount of G should be roughly equal to the amount of C.

Now let's analyze each organism's data:

1. Human:
- A: 30.9%
- T: 29.4%
- G: 19.9%
- C: 19.8%
- Observation: A and T have similar proportions, and G and C also have similar proportions.

2. Chicken:
- A: 28.8%
- T: 29.2%
- G: 20.5%
- C: 21.5%
- Observation: A and T are close in proportions, and G and C are somewhat close in proportions.

3. Grasshopper:
- A: 29.3%
- T: 29.3%
- G: 20.5%
- C: 20.7%
- Observation: A and T match exactly, and G and C are very close.

4. Sea Urchin:
- A: 32.8%
- T: 32.1%
- G: 17.7%
- C: 17.3%
- Observation: A and T are close in proportions, and G and C are also close.

5. Wheat:
- A: 27.3%
- T: 27.1%
- G: 22.7%
- C: 22.8%
- Observation: A and T are almost equal, and G and C are very close.

6. Yeast:
- A: 31.3%
- T: 32.9%
- G: 18.7%
- C: 17.1%
- Observation: A and T are close but not equal, and G and C are close, though not identical.

7. E. coli:
- A: 24.7%
- T: 23.6%
- G: 26.0%
- C: 25.7%
- Observation: A and T are similar, and G and C are close.

Conclusion:
By observing the data from various organisms, it is evident that within a single organism, Adenine (A) and Thymine (T) always seem to occur in relatively similar proportions. Similarly, the proportions of Guanine (G) and Cytosine (C) are also very close to each other. This pattern follows Chargaff's rules, suggesting that in double-stranded DNA, the number of A bases is almost equal to the number of T bases, and the number of G bases is almost equal to the number of C bases across different organisms.