Meiosis
CP Biology 11-4
Meiosis
 Production of sex cells (gametes)
 Egg cells
 Sperm cells
 2 divisions instead of 1
 Results in cells with half the number of
chromosomes
 Human sex cells = 23 chromosomes
Meiosis
 Results in haploid cells
 Human body cells = diploid
 Gametes (eggs and sperm) = haploid
 **At fertilization, chromosome number is
diploid again
 Zygote = 1st cell of new individual (46
chromosomes)
 Half from mom and half from dad
How is Meiosis different from Mitosis?
 One parent cell produces four daughter cells.
 2 cell divisions.
 Daughter cells have half the number of
chromosomes found in the original parent cell
and are genetically different.
 Due to crossing over, each cell gets different DNA
What is crossing over?
 During Prophase I – the chromosomes exchange some of
their genetic material
 Further increases genetic variation in the sex cells
Spermatogenesis
 Process by which sperm cells are made
 Each completion of meiosis produces 4 sperm
cells with 23 chromosomes each
Oogenesis
 Process by which egg cells are made
 Meiosis only produces 1 egg cell each time
Animations of Meiosis
 http://www.johnkyrk.com/meiosis.html
 http://www.sumanasinc.com/webcontent/animations/cont
ent/meiosis.html
 http://www.cellsalive.com/meiosis.htm
 Mitosis vs. Meiosis