The diagram shows a process used in agriculture - HSC - SSCE Biology - Question 34 - 2016 - Paper 1

1. The shaded area indicates regions that require the presence of specific chromosomes, which ensures that the appropriate genetic traits are inherited.

2. It also allows for the maintenance of genetic diversity within the population, crucial for disease resistance and overall survival.

Selective breeding involves choosing specific parents with desirable traits to produce offspring. This process has led to significant changes in agricultural species through the following steps:

1. Identification of Desirable Traits: Farmers identify traits that are beneficial, such as higher yield or disease resistance.

2. Controlled Breeding: Farmers then selectively breed individuals exhibiting these traits over multiple generations, reinforcing these desired characteristics.

3. Observation of Changes: As generations progress, changes in the phenotypes of the species are observed, leading to varieties that are better suited for agricultural practices.

Through this method, crops can be produced that yield more food and are more resistant to pests and diseases, enhancing food security.

A human example of multiple allelism is the ABO blood group system, which has three alleles: A, B, and O. A non-human example can be seen in the Drosophila fruit fly, which has multiple alleles for eye color, influencing the variation seen in this trait.

The graph representing a named polygenic trait, such as height in humans, would typically be bell-shaped. The x-axis represents height, while the y-axis shows the number or percentage of individuals at each height. This distribution illustrates continuous variation, where the majority of individuals are average height, with fewer individuals at the extremes of very short or very tall.