MEIOSIS: Specialized Cell Division

Not just one parent anymore… In asexual reproduction, we looked at animals and plants that need only one parent. This meant that every daughter cell was genetically identical to the parent. Most complicated species require two parents to reproduce.

But things get a bit more complicated… Organisms that reproduce sexually show a greater range in their characteristics. Offspring carry a combination of genetic information from two different parents. Half of the chromosomes come from one parent, and half from the other. This means that there are two genes for every trait – one from mom, and one from dad.

Can just any cell perform meiosis? No. Most cells in the human body are called somatic cells. They undergo only mitosis. Reproductive cells are the only ones that undergo meiosis to reduce the number of chromosomes. What would happen if we didn’t reduce the number of chromosomes?

Okay. So what does meiosis look like? Here we go with the phases again… Now we start with a regular diploid cell. This means it has the regular number of chromosomes for the species. Different species have different numbers of chromosomes. Humans have 46 (23 pairs).

Let the replicating begin! – MEIOSIS I First, we have regular chromosomes in the cell. We call a pair of chromosomes that look the same and carry genes for the same thing homologous chromosomes.

Let the replicating begin! – MEIOSIS I INTERPHASE I Before the division even starts, those chromosomes duplicate.

And then… (STILL MEIOSIS I) Just like before the chromosomes… PROPHASE 1 – the chromosomes shorten and thicken METAPHASE 1 – they line up in the middle of the cell ANAPHASE 1 – they move to opposite sides to get ready to divide

More MEIOSIS I TELOPHASE I - Then the cell divides into two daughter cells. Each cell gets one of each of the doubled homologous chromosomes.

So at the end of MEIOSIS I… But the information is still in duplicate, so they need to split again.

And so begins MEIOSIS II… There is no Interphase this time, since the information is already doubled. Prophase II, Metaphase II, and Anaphase II are all the same again with the pairing up, lining up, and moving to opposite sides.

At the end of… MEIOSIS II TELOPHASE II - During this second part, each chromosome splits in half.

So in conclusion… Meiosis results in 4 sex cells (also called gametes) being formed. These cells are also called haploid because they only contain half of the genetic information. In females, the gametes are called ovum (eggs) and in males they are called sperm.

The saga continues… Each gamete is now ready to continue on its way in the hopes of meeting another gamete (from the opposite sex) and begin a new life…

That’s it for now… Join us on our continuing adventures!!!