Cell Cycle and Cell Division
Meiosis
Meiosis is a special division that halves the chromosome number and makes four cells, each one different. It is how the body makes eggs and sperm.
Meiosis has two rounds of division after just one round of DNA copying. The first round separates the pairs of chromosomes, halving the number. The second round separates the copies, like mitosis. The result is four cells, each with half the chromosomes (haploid).
Two things make the four cells different: chromosomes swap pieces (crossing over), and the pairs line up randomly. This mixing is why siblings are not identical.
Where students slip up
Meiosis halves the chromosome number and needs two divisions, not one. Students often stop after the first division or forget the number is halved. One copying step, two divisions, four haploid cells that are all different.
Hold onto this
One copy, two divisions, four different half-sets.
Why it helps in the exam: crossing over, the two divisions, and 'four haploid cells' are high-yield.
Where this connects
The separating of chromosome pairs in meiosis is exactly Mendel's Law of Segregation happening in real cells. The abstract rule you met in genetics is this physical step.
The rule behind segregation →Quick check
Meiosis produces how many cells from one starting cell, and with what chromosome number?
- ATwo cells, same number
- BTwo cells, half the number
- CFour cells, half the number
- DFour cells, same number