EASY
AS and A Level
IMPORTANT
Earn 100
A phenotypic trait is controlled by two alleles of a single gene D/d. Explain why only the homozygous recessives, dd, can be recognised?
Important Questions on Selection and Evolution
EASY
AS and A Level
IMPORTANT
Calculate the proportions of homozygous dominant and of heterozygous individuals in a population in which the proportion of homozygous recessives is 16%.
EASY
AS and A Level
IMPORTANT
Explain why farmers need to buy maize seed from commercial seed producers each year, rather than saving their own seed to plant.
EASY
AS and A Level
IMPORTANT
With reference to the evolution of antibiotic resistance in bacteria, explain the meaning of the term directional selection.
EASY
AS and A Level
IMPORTANT
List the number of the following statements in the correct order, to explain the evolution of resistance to the antibiotic streptomycin by the bacterium Escherichia coli.
- Most of the population of E.coli is resistant to streptomycin.
- A random mutation in a DNA triplet of a plasmid, changing TTT to TTG, gives an E.coli bacterium resistance to streptomycin.
- The resistant bacterium divides and passes copies of the R plasmid (plasmid with gene for resistance to antibiotic) to its offspring.
- Sensitive bacteria die in the presence of streptomycin as a selective pressure.
- The frequency of the mutated allele in the population increases.
- The resistant bacterium has a selective advantage and survives.
EASY
AS and A Level
IMPORTANT
Hybrids produced by crossing two different inbred (homozygous) varieties are often more vigorous in their growth than either of their parents. Copy and complete the table to show how breeders of maize plants that show hybrid vigour.
Inbred Line 1
| Genotype | homozygous |
| Phenotype | uniform |
| Yield | Low |
Inbred Line 2
| Genotype | _____ |
| Phenotype | _____ |
| Yield | _____ |
Hybrid
| Genotype | _____ |
| Phenotype | _____ |
| Yield | _____ |
EASY
AS and A Level
IMPORTANT
Copy and complete the table to compare artificial selection with natural selection.
| Natural selection | Artificial selection |
| The selective agent is the total environment of the organism | _____ |
| Adaptations to the prevailing conditions are selected | _____ |
| Many traits contributing to fitness are selected | _____ |
