Assistant Laboratory Animal Technician (ALAT) Practice Exam

In which types of cells are chromosomes present but not paired?

1. Red blood cells

2. Ova and sperm cells

3. Skin cells

4. Bone cells

The correct answer is: Ova and sperm cells

Ova and sperm cells, which are also known as gametes, are haploid cells that contain a single set of chromosomes rather than the paired chromosomes found in diploid cells. During sexual reproduction, these cells contribute their genetic material to form a new organism. In humans and many other organisms, each gamete contains 23 chromosomes, which is half the number found in the typical somatic cells that contain 46 chromosomes arranged in 23 pairs. In contrast, red blood cells do not have a nucleus and hence do not contain any chromosomes. Skin cells and bone cells are examples of somatic cells that contain paired chromosomes, as they are diploid and have two sets of chromosomes—one set inherited from each parent. Therefore, the unique formation of chromosomes in gametes, where they exist as unpaired sets, distinguishes them from the paired chromosomal arrangement found in other cell types.