How is a zygote formed in the life cycle of sexual reproducers?

• A. By the division of a diploid cell
• B. By the fusion of two diploid cells
• C. By the replication of a single haploid cell
• D. By the fusion of two haploid gametes

Answer: (D)

Verified step by step guidance

1. Understand the concept of a zygote: A zygote is the initial cell formed when two gametes (sperm and egg) unite during fertilization in sexual reproduction.
2. Recognize the ploidy level of gametes: Gametes are haploid cells, meaning they contain one set of chromosomes. In humans, this is 23 chromosomes.
3. Identify the process of fertilization: Fertilization is the fusion of two haploid gametes, one from each parent, resulting in a diploid zygote.
4. Explain the formation of a diploid zygote: When the haploid sperm and haploid egg fuse, their chromosomes combine to form a diploid cell, the zygote, which has two sets of chromosomes (46 in humans).
5. Clarify why other options are incorrect: A zygote is not formed by the division of a diploid cell or by the replication of a single haploid cell, as these processes do not involve the fusion of two haploid gametes.