Fig. 2 shows three generations of a selective breeding programme for wheat. (a) Name this method of plant improvement. [1] (b) State two desirable character...

Labelled answer diagram:

(a) The method of plant improvement shown in Fig. 2 is selective breeding (also known as artificial selection). [1] The breeder chooses which plants will reproduce based on their observable traits, directing the evolution of the crop over several generations.

(b) Two desirable characteristics a crop breeder might select for in wheat:

1. High grain yield - producing more grain per plant increases the total harvest from a given area. [1]
2. Disease resistance - varieties that resist common fungal diseases such as rust or mildew require less fungicide and suffer fewer yield losses. [1]

Other acceptable answers include drought tolerance, short stem (lodging resistance), uniform ripening, or pest resistance.

(c) The process of selective breeding shown in Fig. 2:

1. The breeder identifies individual wheat plants with the most desirable phenotype, such as those producing the most grain or showing the best disease resistance. [1]
2. These selected plants are cross-pollinated with each other (or allowed to self-pollinate, depending on the programme) to produce seed for the next generation. [1]
3. The offspring are grown and assessed for the target traits. Each plant is evaluated under field conditions to determine which ones best express the desired characteristics. [1]
4. The best-performing offspring are selected for further breeding, and inferior plants are discarded from the programme. [1]
5. This cycle of selection and reproduction is repeated over several generations until the desirable traits are consistently expressed and the population becomes more uniform for the desired characteristics. [1] With each generation, the frequency of favourable alleles increases, producing a more reliable and productive variety.

(d) Two problems resulting from a narrow gene pool in a crop plant:

1. Reduced ability to adapt to changing conditions: With little genetic variation, the crop has fewer alleles available to respond to new environmental challenges such as drought, heat stress, or changing soil conditions. [1] This means an entire variety could fail if growing conditions shift. [1]
2. Vulnerability to disease epidemics: If all plants in a crop are genetically similar, a new pest or pathogen that can attack one plant can attack them all. [1] This increases the risk of catastrophic crop failure across an entire region, as occurred historically with the Irish Potato Famine where genetically uniform potato crops were devastated by blight. [1]