A gamete is a cell containing half the amount of genetic material found in a somatic (body) cell that is capable of joining with another gamete and developing into a new individual. In this sense, the joined gametes (zygote) form the earliest stem cell since this one cell will go on to form a completely new organism.
In humans, there are two types of gametes: the sperm and the ovum (egg). After puberty, men can make more than 1 million sperm per day. On the other hand, women release one mature egg about every 28 days. When a sperm penetrates an egg, a zygote is formed. Very shortly following conception, the genetic material from the sperm joins that of the egg to make a cell that contains the correct amount of genetic material, 46 chromosomes, to make a whole new individual.
Each gamete carries one copy of each of the chromosomes. Thus, the process of fertilization is how each new offspring gets one copy of each chromosome from its father and the other half from its mother. Because each parent has two copies of each chromosome, they pass only one of them to each of their offspring, but they do so randomly, allowing for great genetic diversity. Additionally, there are mechanisms in place to ensure that only one sperm and one egg are allowed to come together during conception. This is important because only the correct amount of genetic material will allow for proper development of the fetus.
If a gamete contains more or less of the number of chromosomes than it should, two outcomes are possible. First, it is likely that the embryo will be spontaneously aborted early in the pregnancy owing to the malformation of the embryo. Alternatively, in some cases, the baby is born with a medical syndrome. The most common chromosomally caused syndromes are Down syndrome (having an extra chromosome number 21), Turner’s syndrome (having only one sex chromosome, an X), and Klinefelter’s syndrome (having more than two sex chromosomes).
There are many other genetic alterations that can be present in the gamete that are harder to detect because they involve small variations in the DNA sequences of the chromosomes. Whether an offspring will develop a particular trait or disease depends on whether the trait is dominant or recessive and if only one or both gametes bring the allele for the trait. When one considers that there are more than 30,000 genes in the human genome, and that there are multiple variations of each gene, it is easy to see why each person is unique.
References:
- Farlex, (n.d.). Gamete. Retrieved from http://encyclopedia.thefreedictionary.com/gamete
- Pierce, (2002). Genetics: A conceptual approach. San Francisco: W. H. Freeman.