A level Biology 17.1 Variation- Exam style question

Question

Phenotypic variation exists in many forms.
(a) Some examples of phenotypic variation in plants and animals are described in Table 2.1.
Complete Table 2.1 by stating whether the cause of variation for each described example is likely to be due to:
• genetic factors, V_G
• environmental factors, V_E
• a combination of genetic and environmental factors, V_G + V_E.

Table 2.1: Examples of phenotypic variation

(b) Name a spontaneous, random event occurring in cells that can be a source of phenotypic variation.
(c) Other than the event named in (b), describe the features of sexual reproduction that contribute to the production of genetically different offspring.

▶️ Answer/Explanation

Solution

(a) Completed Table 2.1:

Explanation:
• Human blood groups (V_G): Entirely genetically determined (ABO system).
• Human height (V_G + V_E): Influenced by genes (e.g., growth hormones) and environment (nutrition).
• Plant leaf color (V_E): Primarily environmental (e.g., sunlight exposure affects chlorophyll).
• Butterfly wing patterns (V_G + V_E): Genetic basis with environmental triggers (e.g., temperature affecting pigment expression).

(b) Mutation

Explanation: Mutations are random changes in DNA that create new alleles, introducing variation (e.g., sickle cell anemia from a point mutation).

(c) Sexual Reproduction Mechanisms:
1. Crossing over: Exchange of genetic material between homologous chromosomes during meiosis.
2. Independent assortment: Random alignment of chromosome pairs during metaphase I.
3. Random fertilization: Any sperm can fuse with any egg, combining unique haploid sets.
4. Random mating: Selection of mates introduces new allele combinations.

Explanation: These processes reshuffle alleles, ensuring offspring inherit distinct genetic combinations from parents (e.g., siblings share ~50% DNA but aren’t identical).

A level Biology 17.1 Variation- Exam style question – Paper 4

Resources

Members

Company