In DNA, the bases adenine (A) and thymine (T) pair together, and guanine (G) and cytosine (C) pair together, so their proportions are expected to be similar within each organism. Let's examine the relative proportions of these bases for several organisms to see if this is true.
To analyze the data, we will look at the absolute differences in the proportions of the base pairs (A-T and G-C) for each organism, then identify the organism with the smallest and largest differences.
Here are the differences calculated for each organism:
1. Human
- [tex]\( |A - T| = |30.9\% - 29.4\%| = 1.5\% \)[/tex]
- [tex]\( |G - C| = |19.9\% - 19.8\%| = 0.1\% \)[/tex]
2. Chicken
- [tex]\( |A - T| = |28.8\% - 29.2\%| = 0.4\% \)[/tex]
- [tex]\( |G - C| = |20.5\% - 21.5\%| = 1.0\% \)[/tex]
3. Grasshopper
- [tex]\( |A - T| = |29.3\% - 29.3\%| = 0.0\% \)[/tex]
- [tex]\( |G - C| = |20.5\% - 20.7\%| = 0.2\% \)[/tex]
4. Sea urchin
- [tex]\( |A - T| = |32.8\% - 32.1\%| = 0.7\% \)[/tex]
- [tex]\( |G - C| = |17.7\% - 17.3\%| = 0.4\% \)[/tex]
5. Wheat
- [tex]\( |A - T| = |27.3\% - 27.1\%| = 0.2\% \)[/tex]
- [tex]\( |G - C| = |22.7\% - 22.8\%| = 0.1\% \)[/tex]
6. Yeast
- [tex]\( |A - T| = |31.3\% - 32.9\%| = 1.6\% \)[/tex]
- [tex]\( |G - C| = |18.7\% - 17.1\%| = 1.6\% \)[/tex]
7. E coli
- [tex]\( |A - T| = |24.7\% - 23.6\%| = 1.1\% \)[/tex]
- [tex]\( |G - C| = |26.0\% - 25.7\%| = 0.3\% \)[/tex]
From these differences, we observe the following:
- Smallest difference in A and T proportions: Grasshopper with [tex]\( |A - T| = 0.0\% \)[/tex].
- Smallest difference in G and C proportions: Human with [tex]\( |G - C| = 0.1\% \)[/tex].
Therefore, the general observation is that in DNA, A and T occur in similar proportions, and similarly, G and C occur in similar proportions. This supports the base-pairing rule in DNA where A pairs with T and G pairs with C.
