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1. **Calculating Allele and Genotype Frequencies:**<br /><br />Given that 10% of the tree population is grey (recessive phenotype), we can use the Hardy-Weinberg principle to calculate allele and genotype frequencies. The Hardy-Weinberg principle states that in a large, randomly mating population, allele and genotype frequencies remain constant from generation to generation in the absence of other evolutionary influences.<br /><br />* **q²:** The frequency of the homozygous recessive genotype (grey) is represented by q². In this case, q² = 0.10.<br /><br />* **q:** The frequency of the recessive allele (g) is represented by q. We can calculate q by taking the square root of q²: q = √0.10 ≈ 0.32.<br /><br />* **p:** The frequency of the dominant allele (G) is represented by p. Since p + q = 1, we can calculate p: p = 1 - q = 1 - 0.32 = 0.68.<br /><br />* **p²:** The frequency of the homozygous dominant genotype (GG) is represented by p²: p² = (0.68)² ≈ 0.46.<br /><br />* **2pq:** The frequency of the heterozygous genotype (Gg) is represented by 2pq: 2pq = 2 * 0.68 * 0.32 ≈ 0.44.<br /><br />Therefore, the allele frequencies are approximately 68% for G and 32% for g. The genotype frequencies are approximately 46% for GG, 44% for Gg, and 10% for gg.<br /><br /><br />2. **Form of Selection:**<br /><br />The question states that only the extreme phenotype (grey) is selected against. This describes **directional selection**. Directional selection favors one extreme phenotype over the other extremes, causing the allele frequency to shift over time in the direction of that phenotype. In this case, the green phenotype is favored, and the grey phenotype is selected against, so the frequency of the G allele will likely increase over time.<br /><br /><br />3. **Differences in Appearance:**<br /><br />The differences in appearance between males and females of the same species are referred to as **sexual dimorphism**.<br /><br /><br />4. **Prezygotic Reproductive Isolating Mechanisms:**<br /><br />Prezygotic isolating mechanisms prevent mating or fertilization from occurring. Here are two examples:<br /><br />* **Habitat Isolation:** Two species might live in the same geographic area but occupy different habitats within that area. For example, one species of frog might prefer to breed in fast-flowing streams, while another prefers stagnant ponds. Even though they live in the same area, they are unlikely to encounter each other to breed.<br /><br />* **Temporal Isolation:** Two species might breed during different times of day or different seasons. For example, one species of plant might flower in the spring, while another flowers in the fall. This difference in timing prevents them from cross-pollinating.<br />