During secondary succession, which of these best describes why decomposing pioneer plants give way to larger, more complex plants species, such as hardwood trees?
A) Increased amounts of sunlight are able to reach the ground while the pioneer species are decomposing.
B) Increased soil temperatures from decomposing pioneer species help tree seeds germinate more quickly.
C) Increased amounts of decomposing pioneer species remove nutrients that tree seedlings need to grow and mature.
D) Increased amounts of soil from decomposing pioneer species allow plants with more extensive root systems to become established.

The statements that apply are the third and the fourth.

Explanation:

Since the mice crossed were pure breeding, each parent produced sperms of one kind, both alleles of each parente were equal. Thus, the first (A) and second (B) statements are false.

Assume pure breeding black mice produced BB sperm and pure breeding brown mice produced bb sperm.

The punnett square for the first generation, F₁ is would be:

         b       b

B        Bb    Bb

B        Bb    Bb

This is, all the F₁ generation mice are Bb.

All the 992 in F₁ generation had black coats means black is dominant.

Now when F₁ generation is crossed, the punnet square reveals the second generation, F₂:

         B      b

B        BB    Bb

b         bB    bb

The brown allele that was hidden now appears.

Based on the assumption that black is dominant, BB, Bb and bB are black, which is 3/4 or 75%. This, is 75% of the mice in the F₂ genrertion are black.

The combination bb is brown. Thus, 1/4 or 25% of the mice in the F₂ generation are brown.

When the mice in the first generation were crossed, they yielded 961 black coated mice and 317 brown coated mice. That is:

Total mice: 961 + 317 = 1278Proportion of black mice: 961 / 1278 ≈ 0.75 = 3/4Proportion of brown mice: 317 / 1278 ≈ 0.25 = 1/4Ratio black to brown: 3 to 1.

Therefore, it is proven that an approximately three-to-one ratio of black to brown cated mice in F₂ is accounted fro the black allele being dominant over the  brown allele (choice C.)

Also, the brown allele is not independent from the black allele and dissapears in the F₁ generation: it is not independent because it presence will only be shown when the black allele is not present, and it is said that it dissapears because it is not revealed, it is hidden.