What occurs during the fusion of gametes, and how does it result in diploid zygotes with two alleles of each gene?

SouravNovember 8, 2024

Answer

The fusion of gametes, known as fertilization, is a critical process in sexual reproduction that leads to the formation of a diploid zygote. This process involves several key steps that result in the combination of genetic material from two parents, ultimately restoring the diploid chromosome number.

Process of Gamete Fusion

1. Gamete Characteristics:
   • Gametes are haploid cells, meaning they contain only one set of chromosomes. In humans, this includes 23 chromosomes in sperm and 23 chromosomes in the egg (ovum).
2. Fertilization:
   • Fertilization occurs when a male gamete (sperm) successfully penetrates and fuses with a female gamete (egg). This process involves several stages:
     • Recognition and Adhesion: Sperm must recognize and adhere to the egg’s surface, facilitated by specific proteins on both gametes.
     • Membrane Fusion: The membranes of the sperm and egg fuse, allowing the sperm to enter the egg. This fusion is mediated by various proteins that facilitate the merging of their lipid bilayers .
3. Formation of the Zygote:
   • Once the sperm enters the egg, it contributes its haploid set of chromosomes to the egg’s haploid set. This results in a single diploid cell called a zygote, which contains two sets of chromosomes—one from each parent.
   • The zygote thus has two alleles for each gene, one inherited from the mother and one from the father. For example, if one parent contributes an allele for brown eyes (B) and the other contributes an allele for blue eyes (b), the zygote may have a genotype of Bb.
4. Pronuclear Fusion:
   • After fertilization, the sperm’s nucleus (now referred to as the male pronucleus) and the egg’s nucleus (female pronucleus) migrate towards each other within the zygote. The nuclear membranes break down, allowing these two pronuclei to fuse—a process known as karyogamy—to form a single diploid nucleus.
   • This fusion restores the diploid state (2n), where n represents the haploid number of chromosomes.
5. Zygote Development:
   • Following fertilization, the zygote undergoes rapid mitotic divisions known as cleavage, leading to the formation of an embryo. During these divisions, genetic material is replicated and distributed among new cells