MEIOSIS
(textbook section 3.1 pg 74)

Sexual reproduction produces offspring that is genetically
similar, but different from the parents. This is accomplished by
having two sex cells that each have half the information (half
the chromosomes) combine to form a cell. The process to
make a sex cell is called meiosis.

Multi-cellular organisms (like you) have two cell types:

Somatic cells – called body cells (things like skin, stomach, etc)
reproduce by mitosis. They each have 23 pairs of chromosomes
for a total of 46 chromosomes.

Gamete cells – called sex cells (sperm and egg) reproduce by
meiosis. They each have one half of each of the 23 chromosome
pairs.

Members of the same species have the
same number of chromosomes. Humans
Gametes
have 46.
cannot have 46
chromosomes or else when they
combined the new cell would have 92
chromosomes. Since gametes have half
the number of chromosomes they are
called haploid (23 chromosomes). Somatic
cells are diploid (46 chromosomes).

HAPLOID CELLS HAVE ONE SET OF EACH CHROMOSOME (23
TOTAL FOR HUMANS) AND DIPLOID CELLS HAVE TWO SETS OF
EACH CHROMOSOME (46 TOTAL FOR HUMANS)

In diploid cells chromosomes come in pairs. These are called
homologous pairs (homologous chromosomes). One half of
the pair comes from the mom, the other from the dad. Each
half contains genes for the same protein at the same location.

Meiosis is similar to mitosis, but it differs in some very important
ways. First is that Meiosis results in the creation of 4 haploid cells,
not 2 diploid cells. Secondly, Meiosis creates 4 daughter cells with
half the number of original chromosomes, whereas Mitosis
produces 2 cells that contain the same amount of chromosomes
(See handout on Meiosis).

Pg 78. #1, 2, 4, 5, 8, 9, 12, 15, 16