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Meiosis
Section10.2
Diploid and haploid cells
• In the body cells of animals and most plants,
chromosomes occur in pairs.
• A cell with two of each kind of chromosome
is called a diploid cell and is said to contain a
diploid, or 2n, number of chromosomes.
•A cell containing one of each kind of
chromosome is called a haploid cell and is
said to contain a haploid, or n, number of
chromosomes.
• Meiosis consists of two separate divisions,
known as meiosis I and meiosis II.
• Meiosis I begins with one diploid (2n) cell.
• By the end of meiosis II, there are four
haploid (n) cells.
Process of Meiosis
I – begins with 1 cell 
46 chromosomes (in humans)
 Meiosis
– Prophase I (DNA pairs have doubled)
• Crossing over occurs
– Metaphase I
– Anaphase I
– Telophase I
 Ends with two cells
– With 23 chromosomes each
Process of Meiosis
 Meiosis II
– 2 Daughter cells  23 -sister chromatids
– Prophase II (NO DNA doubling)
– Metaphase II
– Anaphase II (Sister Chromatids split in half)
– Telophase II
 Ends with 4 daughter cells  23
single chromosomes
– Each different from each other
Crossing over
Chromosomes exchange pieces during
meiosis I
 Gives offspring more genetic variance
 Offspring are different

Crossing over