Fertilization adds two sets of chromosomes
- The idea
- Predict
- See it
- Why
- Check
The idea
“When two gametes fuse, the zygote ends up with the same number of chromosomes as each gamete.”
Two cells become one, so it's easy to picture the count staying put. Fusion actually keeps every chromosome from both cells.
The short version
The mistake: When two gametes fuse, the zygote ends up with the same number of chromosomes as each gamete.
What's actually true: Fertilization combines two haploid sets, so the zygote has the egg's chromosomes plus the sperm's.
- A gamete is haploid, written n. It holds one set of chromosomes, one of each kind.
- Fertilization adds the egg's set to the sperm's set. The zygote is diploid, 2n, with two of each kind, called homologous chromosomes.
- Meiosis halves the number when the next gametes form. Halving then adding keeps the count the same from one generation to the next.
On the exam: Fertilization adds two sets together. Meiosis is the step that halves.