A typical sperm cell contains approximately half the amount of DNA found in a normal human somatic cell. More specifically, a human sperm cell contains, on average, about 1.22 arbitrary units of DNA, compared to roughly 2.66 arbitrary units in somatic cells.
This halved amount is crucial for sexual reproduction. When a sperm fertilizes an egg (ovum), which also contains half the amount of DNA of a somatic cell, the resulting zygote receives a full, complete set of DNA, ensuring the correct genetic makeup of the offspring. The DNA content in sperm cells remains remarkably consistent among fertile males. This consistency highlights the importance of accurate DNA replication and segregation during sperm development (spermatogenesis).
Essentially, sperm cells (and egg cells) are haploid, meaning they have one set of chromosomes (23 in humans), while somatic cells are diploid, meaning they have two sets of chromosomes (46 in humans). This difference ensures that when the haploid sperm and egg fuse, the diploid state is restored in the zygote.
