Cell division only
for sex cells:
Meiosis 1:
- homologous chromosomes
- attached together
- point of attachment is the chiasmata
- cross-over...so their genes are exchanged
- chromosomes line up at equator
- spindle fibres from centrioles, attach to centromeres
- end of Meiosis 1, chromosomes are randomly pulled by the spindle fibres, from the centrioles, to give two daughter cells.
Meiosis 2:
- chromosomes with 'exchanged genes' have spindle fibres
- spindle fibres attach to the centromere
- crhomosomes into chromatids
- pulled randomly
- end of Meiosis 2, four daughter cells haploid cells formed
Advantages of meiosis:
1. sperm and egg are haploid cells.
n+n=2n
-therefore genetic variation
-1/2 from father and 1/2 from mother.
2. independent assortment of chromosoems:
-crossing-over
-Meiosis 1, chromosomes are pulled randomly
-Meiosis 2, chromatids are pulled randomly
Meiosis
1.
2.