Advanced Placement (AP) Biology Practice Exam

What is characteristic of a polyploid organism?

1. It has an abnormal number of chromosomes

2. It has additional sets of chromosomes

3. It has one X chromosome inactivated

4. It has reversed chromosomal segments

The correct answer is: It has additional sets of chromosomes

A polyploid organism is characterized by having additional sets of chromosomes beyond the typical diploid number. In polyploidy, cells contain multiple complete sets of chromosomes, such as triploid (three sets) or tetraploid (four sets). This condition can arise naturally through processes such as whole genome duplication or through hybridization between species. Polyploidy is common in many plant species and plays a significant role in evolution, speciation, and adaptation. While an abnormal number of chromosomes may suggest a deviation from the normal diploid state, this term is too vague and can apply to other genetic conditions, such as aneuploidy, which involves the gain or loss of individual chromosomes rather than entire sets. The inactivation of one X chromosome pertains specifically to dosage compensation in female mammals and is not relevant to the definition of polyploidy. Similarly, the notion of reversed chromosomal segments relates to chromosomal rearrangements rather than the essence of being polyploid.