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I'm assuming that this question is asking about a human zygote, but it's important to have this information established because the number of chromosomes in a zygote can be very different depending upon the species being discussed. For example, some plant species can have more than two sets of chromosomes.
A zygote is normally the result of fertilization, or fusion, between two gametes, such as a sperm and egg. Gametes each have one copy of the organism's chromosomes, the number of which is often represented by the variable n. Zygotes thus have 2n chromosomes; in humans this number is 46. Since there are two copies of every chromosome, every gene should be found on two chromosomes.
In practice this isn't necessarily the case; for example, chromosomal disorders can cause duplication or deletion of genes, resulting in the organism having one, none, or more than two copies of the gene. This is also the normal state for males, because the Y chromosome is smaller than the X chromosome and therefore contains fewer genes, leaving some of the X genes unpaired.
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