Sexual reproduction is the process in which two gametes, sperm and egg, come together to form one fertilized cell, called a zygote, which contain genetic information from both parental cells.

Each species of organisms has a certain number of chromosomes that occur in pairs. For example, human body cells have 23 pair or 46 chromosomes. The chart below shows some organisms and the number of chromosomes in the body cells.

If 46 chromosomes in an egg joined with 46 chromosomes in a sperm then the zygote would have 96 chromosomes. What process regulates the number of chromosomes in each species?

The answer to this is a specialized cell division called meiosis Most plant and animal cells are diploid. The term diploid is derived from the Greek diplos, meaning “double” or “two”; the term implies that the cells of plants and animals have two sets of chromosomes. Diploid is often noted as 2N where N is the number of chromosomes. So in humans 2N=46.

During sexual reproduction, the sex cells of parent organisms unite with one another and form a fertilized egg cell. In this situation, each sex cell is a gamete. The gametes cells are haploid, from the Greek haplos, meaning “single.” This term implies that each gamete contains a single set of chromosomes—23 chromosomes in humans. When the human gametes unite with one another, the original diploid condition of 46 chromosomes is reestablished. Haploid is often noted as N. So in humans N=23.

Image adapted from: haploid vs diploid chromosomes, Sparknotes

Watch this video for an overview of what happens during meiosis.

What did you learn?

1. How many daughter cells are produced at the end of meiosis? Interactive popup. Assistance may be required.

   Check Your Answer

   four
2. Are the daughter cells haploid or diploid? Interactive popup. Assistance may be required.

   Check Your Answer

   haploid