Four gametes are made during cell division by meiosis. The gamete cells have half the number of chromosomes as the cell.
Click on image for full size
Courtesy of National Center for Biotechnology Information, NIH
Cell Division by Meiosis
Plants, animals and many other species within the domain Eukaryota are able to make more individuals by sexual reproduction. In its simplest form, this means that offspring are made from gametes. Gametes are cells with only half the number of chromosomes as the organism. When two gametes fuse together, the number of chromosomes is correct, with half of those chromosomes (one from each pair) coming from the mother and the other half coming from the father. This set of chromosomes becomes the genetic instructions that describe how the individual will grow and develop.
Forming the gametes requires cells to undergo a special type of cell division called meiosis, which is really two cell divisions happening one after the other. Meiosis will only occur in cells in the male or female sex organs of the plant or animal.
Step 1: In this first phase, called Meiosis I, two daughter nuclei are made from the nucleus of one cell. In a process similar to mitosis, a cell forms two daughter cells that each have a single set of chromosomes, half the total number in the original cell.
Step 2: Each of the two daughter cells is divided into two making four gametes. This step is called Meiosis II but it is really the same process as mitosis.
Gametes only contain one copy of each gene, but the cell they were made from contained two varieties of each gene. The genes in each gamete are chosen randomly from each pair of alleles during meiosis. One variety or the other will be passed on to the offspring.
Last modified April 13, 2004 by Lisa Gardiner.
Shop Windows to the Universe Science Store!
The Spring 2010 issue of The Earth Scientist
, focuses on the ocean, including articles on polar research, coral reefs, ocean acidification, and climate. Includes a gorgeous full color poster!
You might also be interested in:
Though not the largest kingdom, with a mere 300,000 species catalogued, many might argue that the Kingdom Plantae just may be the most important group of living organisms. In the process known as "photosynthesis",...more
Do you look a bit like your siblings? Do you and your siblings look a bit like your parents? The similarities are because, unless you were adopted, you and the other members of your family have genetic...more
Jupiter's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +32 degrees (freezing temperature)....more
In July, 1996, it was announced that Dr. David McKay, along with a team of scientists at Johnson Space Center (a division of NASA), had discovered possible fossils of bacteria in an ancient rock from Mars....more
Saturn's atmospheric environment is one of strong gravity, high pressure, strong winds, from 225 miles per hour to 1000 miles per hour, and cold temperatures of -270 degrees to +80 degrees. With winds...more
Titan's atmosphere is a lot like the Earth's, except that it is very cold, from -330 degrees to -290 degrees! Like the Earth, there is a lot of Nitrogen and other complex molecules. There also may be an...more
Autotrophs are organisms that produce organic compounds from an inorganic source of carbon (carbon dioxide) given a source of energy. If the source of energy is the reactions of inorganic chemical compounds,...more