Table 1 shows the wing lengths of beetles collected from two sides of a new road. Fig. 1 shows that the road separates patches of grassland. Before the road...
Question 1 Report
Table 1 shows the wing lengths of beetles collected from two sides of a new road. Fig. 1 shows that the road separates patches of grassland. Before the road was built, beetles could move freely between the patches. The students collected beetles using identical pitfall traps for the same 24-hour period in June. They measured wing length to the nearest 0.1 mm and returned the beetles to their capture sites. The students think the smaller population on the eastern side may lose alleles by chance, rather than because one wing length is always better for survival.
| site | number of beetles sampled | mean wing length / mm | range / mm |
|---|---|---|---|
| west grassland | 32 | 8.6 | 7.4-10.2 |
| east grassland | 11 | 8.5 | 7.8-9.1 |
(a) Use Table 1 to state which site has the larger range of wing lengths. [1]
(b) Name the chance change in allele frequency that is more likely in a small isolated population. [1]
(c) Suggest two ways the road could reduce gene flow between the beetle populations. [3]
The diagram shows a grower using cuttings from one strawberry plant to fill a greenhouse bench. Each cutting develops roots and becomes a new plant. A second bench contains plants raised from seeds after cross-pollination by insects. Both benches are given equal amounts of water and kept at 20 degrees C. After a fungal disease appears, the grower counts infected plants. The grower also measures fruit mass because the original parent plant had large fruit. Fig. 1 shows the two methods used to produce the plants.
(a) Describe the genetic relationship between plants produced from cuttings. [1]
(b) Suggest why the seed-grown bench is likely to show more variation in fruit mass. [2]
(c) Use Fig. 1 to state one advantage of using cuttings for commercial strawberry production. [2]
Answer Details
Labelled answer diagram:
Beetle populations
(a) West grassland has the larger range [1]. Its range is \(10.2-7.4=2.8\) mm, compared with \(9.1-7.8=1.3\) mm in east grassland.
(b) The chance change in allele frequency is genetic drift [1]. It has a greater effect in small populations because chance loss of alleles represents a larger proportion of the gene pool.
(c) The road forms a physical barrier [1], so fewer beetles cross it to mate [1]. Consequently, fewer alleles are exchanged between the populations, which breed mainly within themselves [1]. This reduces gene flow.
Strawberry production
(a) Plants produced from cuttings are clones: they are genetically identical to the parent and to each other [1].
(b) Seed-grown plants result from sexual reproduction [1]. Meiosis and fertilisation produce different combinations of alleles [1], so fruit mass is more likely to vary.
(c) Cuttings retain the parent's desirable large-fruit genotype [1], and many plants can be produced quickly [1]. No seeds or pollinators are needed.
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