They often are very similar in structure and appearance. A sperm is a male sex cell. It fuses with an egg to produce a new individual. One of the 4 bases that makes up the rungs in the DNA ladder. They have two copies of each gene found on the X chromosome.
Boys only have one X chromosome.
They also have a smaller Y sex chromosome. There is a gene on the Y chromosome that tells a baby to be a boy. This zygote then divides many times to form a new individual.