Help! I’m totally lost with meiosis
Hi everyone, I’m preparing for my biology exam and meiosis is killing me. I understand mitosis pretty well, but meiosis has so many steps and I mix up everything. Why do we need two divisions? What is actually happening with chromosomes? Can someone explain in simple words what are the main differences between meiosis I and II and why crossing over is important? Thank you so much!!
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Hey, don’t worry, many people struggle with this topic at first. Meiosis is the special division that creates sperm and egg cells with half the normal number of chromosomes. It has two rounds of division: Meiosis I and Meiosis II.
The key point of Meiosis I is that homologous chromosomes (one from mom, one from dad) separate. Because of this, the daughter cells become haploid (n instead of 2n). During prophase I happens crossing over — this is when parts of maternal and paternal chromosomes are exchanged. That creates new combinations of genes. Then in metaphase I homologous pairs line up and in anaphase I they are pulled to opposite poles.
Meiosis II is very similar to mitosis — here sister chromatids separate. That’s why we end up with four different haploid cells instead of two identical ones.
The most detailed explanation of all stages you can find here: phases of meiosis
Crossing over and independent assortment (random alignment in metaphase I) are the two main reasons for genetic variation — without them all siblings would be almost genetically identical. Meiosis keeps chromosome number constant across generations and provides raw material for evolution.