Reproduction can produce offspring which are: • genetically different or • genetically identical - AQA - GCSE Biology - Question 9 - 2023 - Paper 2

One advantage of growing genetically identical tomato plants is that they ensure uniformity in yield and growth rates, making harvesting and marketing more efficient.

Tissue culture is a technique in which cells are grown in a controlled environment outside their natural conditions. It enables the propagation of genetically identical plants from a small tissue sample.

One reason genetically identical tomato plants may not grow to the same height is due to environmental factors such as varying water availability, light conditions, or nutrient levels in the soil.

The Punnett square would be completed as follows:

This shows that there is a 50% probability of having female offspring (XX) and a 50% probability of male offspring (XY).

The probability of having three male and three female offspring from a total of six is calculated using the binomial distribution formula, considering equal probabilities of male and female offspring. The probability is:

$P(X=k) = \binom{n}{k} p^k (1-p)^{n-k}$

Where n = total offspring, k = number of males, p = probability of male offspring. Thus, $P(3 \text{ males}) = \binom{6}{3} (0.5)^3 (0.5)^3 = 20 \times \frac{1}{64} = \frac{20}{64} = 0.3125, \text{ or } 31.25\%.$

The farmer used a large number of chickens to ensure that the results were valid and representative, reducing the impact of anomalies and providing more reliable mean values.

Selective breeding of chicken varieties A and B involves mating individuals with desirable traits, such as high meat yield and egg production. The offspring would be evaluated for these traits, and only the best individuals would be bred together. This process would be repeated over multiple generations to establish a new variety that consistently demonstrates both high meat production and egg-laying capability.