Download Meiosis - WordPress.com

Meiosis
Chapter 5 Section 3
Asexual –VS- Sexual Reproduction
• Asexual Reproduction
• Genotype of offspring are exact
copy of parent.
• Only ONE parent is needed.
• Cells divide through a process
called mitosis.
• Body (somatic) cells reproduce this
way.
• Most single-celled organisms
reproduce this way.
• Sexual reproduction
• Genotype of offspring is shared
from both parents
• TWO Parents are needed.
• Sex cells (gametes) are made
during meiosis.
• Gametes have half (haploid) the
number of chromosomes as the
body cell.
• Two gametes combine to form a
somatic (body) cell with the full
number of chromosomes (diploid).
Meiosis – a process in cell division in which the
number of chromosomes is reduced by half which
results in the production of sex cells.
Prophase I:
• Threadlike
chromosomes copy
themselves and form
thick, short, visible
chromatids.
• The nuclear
membrane disappears.
• Crossing over occurs.
Metaphase I:
Homologous
pairs line up in
the center of the
cell.
Meiosis I Continued
Anaphase I
Homologous
chromosomes pull
apart – but sister
chromatids are still
attached.
Telophase I
The nuclear
membrane reforms
and the cell divides.
(cytokinesis)
**The sister
chromatids are still
joined.
Product of Meiosis I
At the end of Meiosis I there are
two cells, each with a haploid (half)
number of chromosomes consisting of a
pair of sister chromatids.
Meiosis 2
Prophase II
• Each cell contains
one member of
each homologous
pair.
• Nuclear membrane
dissolves.
• Chromosomes are
NOT copied.
Metaphase II
Sister chromatids line
up at the center of the
cell.
Meiosis 2 Continued
Anaphase II
Sister chromatids pull apart
and move to opposite ends
of the cell.
Telophase II
• Nuclear membrane
reforms.
• Cells divide (cytokinesis)
Product of meiosis II
The end result of meiosis
is the production of 4
haploid gametes.
(4 sex cells (sperm/egg) with half the
number of chromosomes)