Final answer:
Artificial selection ensures that traits preferred by humans are present in a population, often reducing genetic variation rather than increasing it and does not ensure the removal of all disease traits or inherently increase the likelihood of mass extinction.
Step-by-step explanation:
Artificial selection is a form of biotechnology that involves the selective breeding by humans to propagate desirable traits in plants or animals. One true statement about artificial selection is that it ensures traits preferred by humans are present in a population. For instance, farmers may breed cows that produce high-quality milk and avoid breeding those with lower milk production, leading to an increased milk quality and quantity in the herd.
However, this process does not necessarily increase the genetic variation in a population. Instead, it may actually reduce genetic diversity by consistently favoring certain traits over others. Additionally, artificial selection does not ensure that all traits for disease are removed from a population, as not all genetic diseases or predispositions are necessarily understood or targeted during selective breeding. Lastly, while artificial selection could potentially contribute to the vulnerability of a population to mass extinction due to reduced genetic variation, it does not inherently increase the likelihood of mass extinction.