Fig. 1 shows a microscope field containing pollen grains from a single species of grass. A genetics class counted grains with either a smooth outer wall or ...
Question 1 Report
Fig. 1 shows a microscope field containing pollen grains from a single species of grass. A genetics class counted grains with either a smooth outer wall or a spiny outer wall. The grain type is controlled by alleles, whereas the actual diameter of a pollen grain is measured as a continuous value.
Table 1 gives counts from 150 pollen grains.
| outer-wall type | number of pollen grains |
|---|---|
| smooth | 112 |
| spiny | 38 |
(a) What type of variation is outer-wall type? [1]
(b) Give the percentage of pollen grains with spiny walls. [1]
(c) Describe why the two wall types are unlikely to be caused by different amounts of water in the plant. [2]
(d) What type of variation would pollen-grain diameter show? [1]
Answer Details
Outer-wall type has distinct inherited forms, whereas diameter is a measurement with intermediate values.
- Outer-wall type is discontinuous variation. [1]
- \[\frac{38}{150}\times100=25.3\%\]25.3%, or 25%. [1]
- Water availability may affect pollen-grain size, but it would not produce distinct inherited smooth and spiny wall categories. The smooth or spiny form is determined by alleles or genes. [2]
- Pollen-grain diameter shows continuous variation. [1]
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