Science Buddies: "Ask an Expert"

How does meiosis occur in males or females whom havent been fertilized yet? Cuz the crossing over involves homologous chromosomes...Isnt tht supposed to be happening in females which had been fertilized only?

Hello NigelAng,

Meiosis is the process by which an organism produces gametes (the germ cells that when combined will form an embryo - such as sperm from males and egg from females). Every person is diploid (has two sets of chromosomes - one from their mom and one from their dad -- these came from the egg and sperm which came together to produce the embryo that eventually grew up into a person). This means that all of our cells have two copies of each chromosome. But in order to make sure that the next generation will also have only two copies of each chromosome in their cells there needs to be a special process so that the sperm and egg cells (which make up the next generation) only have ONE copy of each chromosome. This special process is meiosis.
The crossing-over process occurs when the homologous chromosomes line up at the start of the process - the one that came from mom and the one that came from dad. As the process continues the chromosomes will end up separating into different cells so that each cell only has one copy of each chromosome (haploid). And it is these cells which become eggs and sperm and when they come together during fertilization they will make an embryo that once again has two copies of each chromosome.
Here are some links that might explain things better.
https://www.youtube.com/watch?v=pdJUvagZjYA
https://www.khanacademy.org/science/bio ... -meiosis-i

Hope this helps, if not please let us know.

Elizabeth