Advanced Placement (AP) Biology Practice Exam

What term describes a diploid fertilized egg?

1. Gamete

2. Zygote

3. Tetrad

4. F1 generation

The correct answer is: Zygote

A diploid fertilized egg is referred to as a zygote. When a sperm cell (which is haploid) fertilizes an egg cell (also haploid), the two gametes combine their genetic material to form a zygote, which now contains a complete set of chromosomes — one set from each parent, resulting in a diploid organism. This is the initial stage of embryonic development where the genetic contribution of both parents is amalgamated, leading to the formation of all subsequent cells in the developing organism. In contrast, a gamete refers to a reproductive cell (sperm or egg) that is haploid, meaning it has only one set of chromosomes. A tetrad describes a structure that forms during meiosis when homologous chromosomes pair up, and the F1 generation signifies the first filial generation resulting from a cross between two parent organisms.