Meiosis
Cell division – ‘reduction
division’
Production of sex cells –
gametes
Why do we need meiosis?
Meiosis is necessary to halve the
number of chromosomes going into the
sex cells
Why halve the chromosomes in gametes?
At fertilization the male and female sex
cells will provide ½ of the chromosomes
each – so the offspring has genes from
both parents
How many chromosomes does a
human have?
chromosomes total- 46
23 from male sperm
23 from female egg
What is meiosis?
Meiosis has two rounds of cell
division, meiosis I and meiosis II
each subdivided into prophase,
metaphase, anaphase and
telophase.
Results in 4 daughter cells, each
with half of the genetic material of
the original cell.
Parent cell
Chromosomes are
copied and double
in number
Chromosomes
now split
2 daughter cells
identical to original
Meiosis
Parent cell –
chromosome pair
Chromosomes
copied
1st division - pairs split
2nd division – produces
4 gamete cells with ½
the original no. of
chromosomes
Meiosis – mouse
Parent cell
1st division
2nd division
4 gametes
Function of Meiosis
Meiosis is a process that occurs
for the following functions:
To reduce the chromosome number
from diploid to haploid. This is called a
reduction division
To ensure that each haploid cell has a
complete set of chromosomes
To promote genetic diversity because
each cell is unique.
Compare mitosis to meiosis
Mitosis
Meiosis
Produces genetically
identical cells
Produces genetically
unique cells
Results in diploid cells Results in haploid
cells
Takes place
throughout life
Takes place only at
certain times
Involved in asexual
reproduction
Involved in sexual
reproduction
Meiosis