Transcript Meiosis

Meiosis: Making reproductive cells
Meiosis: the process of nuclear division where
the number of the chromosomes is halved.
• produces four daughter cells
• all daughter cells are haploid (n)
• chromosomes are shuffled in the process, so
that each daughter cell has a unique
combination (it produces many different
reproductive cells.)
• process that makes gametes (sperm and egg)
Crossing-Over
- Chromosomes exchange sections
- Crossing over increases variability/diversity
- Crossing-over increases the already huge number of
different gamete types produced by independent assortment
Spermatogenesis: Production of male gametes (sperm)
Oogenesis: Production of female gametes (eggs)
Spermatogenesis
Occurs in the
testes
Two divisions
produce 4 sperm
cells
Men produce about
250,000,000
sperm per day
Oogenesis
Occurs in the ovaries
Two divisions produce 3 polar bodies
that die and 1 egg
Polar bodies die because of unequal
division of cytoplasm
Starting at puberty,
one egg matures
every 28 days
Comparing
Mitosis and
Meiosis
Mitosis vs. Meiosis
Mitosis
• Cell division of body
cells (somatic)
• Produces 2 diploid
cells (2n)
• Each new cell contains
copies of all
chromosomes
• One cell division
• All cells are identical
(photocopies)
Meiosis
• Cell division that
produces gametes
• Produces 4 haploid
cells (n)
• Each gamete contains
just one chromosome of
each pair
• Two cell divisions
• All cells are different
(diversity)
Fertilization