A pure-breed black cow is crossed with a pure-breed red bull - NSC Agricultural Sciences - Question 4 - 2019 - Paper 2

The justification states that all the F1 offspring exhibit the black color, demonstrating that black is dominant over red.

a) The genotype of the cow is homozygous dominant, represented as BB.

b) The genotype of the offspring is heterozygous, represented as Bb.

The type of crossing being utilized is identified as dihybrid crossing, which involves two traits being studied simultaneously.

This dihybrid crossing allows for the observation of inheritance patterns between two different characteristics, which in this case are texture and color.

Two possible phenotypes of the F1 generation could be:

1. Green rough
2. Yellow smooth

To determine the percentage of offspring that are yellow and smooth, the calculation is:

$\left( \frac{1}{16} \right) \times 100 = 6.25\%$

The term for the phenomenon addressed in the statement is variation, which refers to the differences in traits within a species.

1. Nutrition/diet/feeding can significantly influence trait expression.
2. Climate factors such as light intensity, temperature, and rainfall can affect growth and development.

1. Artificial selection is a process where humans select specific traits.
2. Natural selection occurs in nature, favoring individuals with advantageous traits.

The breeding system in question is crossbreeding, which is the practice of breeding different breeds or varieties.

The reason for this is that different or unrelated breeds of the same species are combined, such as beef breeds crossed with dairy breeds.

1. Cross breeding significantly increases genetic variation, enhancing the pool of traits.
2. It can result in heterosis or hybrid vigor, leading to improved performance in offspring.

1. Inbreeding can lead to a loss of genetic variation.
2. It may also result in inbreeding depression, increasing the expression of detrimental traits.

The Punnett square for the F2 generation should display the potential gametes and their resulting combinations. This will illustrate the expected offspring ratios.

a) The genotypic ratio can be stated as 1:1:2:2 for the F2 generation.

b) The percentage of offspring with a certain genotype is 0%.

The genotype of the highest maize plant is identified as AABBDD based on its phenotypic expression.

The calculation for the length of the longest maize plant is as follows:

$40 + 5 + 5 + 5 + 5 + 5 = 30cm$ Total height = 70cm.

Two genotypes of maize plants that will grow to be 55cm long may include:

1. AABbdd
2. AaBbdd

1. Retroviral vectors
2. Micro-injection
3. Embryonic stem cells
4. Gene editing techniques, such as CRISPR.