Meiosis: Diploid, 2n, to Haploid, n
Donna Huffman
Biology Lab Instructor
Calhoun Community College
Introduction
All living things must reproduce to survive.
All body or somatic cells reproduce by mitosis
which is simple cellular reproduction.
All sex cells must reduce their chromosome
number as they divide. This reduction division is
called meiosis and changes the chromosome
number from Diploid, 2n, to Haploid, n.
Each offspring resulting from the combination of
haploid sex cells will contain the same
chromosome number as their parents.
Mitosis
The Big Picture
somatic (body) cells
2n
Meiosis
sex cells (sperm or egg)
2n
2n = Diploid
n = Haploid
n
2n
n
2n
n
n
n
n
Diploid vs. Haploid
Diploid (2n) = Full complement of chromosomes
found in any somatic cell of an organism
Haploid (n) = Half the number of chromosomes
found in a diploid cell. Sex cells have a haploid
number of chromosomes.
For example:
Human cheek cells have 46 chromosomes. (Diploid)
Human sex cells have 23 chromosomes. (Haploid)
Meiosis
male
sex cell
production
2n
n
n
Haploid
n
n
n
n
n
n
n
female
sex cell
production
2n
Diploid
n
sperm
n
egg
2n
Diploid Zygote
Fertilization
n
Each somatic cell
nucleus contains the
2n or diploid number
of chromosomes.
Each of these human
somatic cheek cells
contains 46
chromosomes.
Each nucleus has all
the information
needed for an entire
organism.
Somatic Cells
Cheek cell nuclei
2n
Photomicrograph of Nuclear
Chromosomes
Meiosis
2n
n
Meiosis in the male and female divides each diploid
cell into 4 haploid sex cells.
At what point in Meiosis does the chromosome
number change from Diploid to Haploid?
2n Prophase I
centromere =
n Anaphase I
n Telophase II
The homologous pair in Prophase I separates in Anaphase I thus
changing the number of the chromosomes from Diploid to Haploid.
Female Meiosis: Oogenesis
Oogenesis occurs within the ovary as an immature follicle
develops into a mature follicle containing an egg.
immature follicle
mature follicle with egg
Female: Diploid to Haploid
Ovary
2n
Egg producing Follicle
Egg
n
Male Meiosis: Spermatogenesis
Spermatogenesis occurs in the testis as cells within the
wall of the seminiferous tubule divide from diploid
somatic cells into mature haploid sperm.
1N
2N
seminiferous tubule
mature sperm
Male: Diploid to Haploid
2n
Testis
n
10X photomicrograph
of testis cross section
Sperm
Conclusion
n
+ n
=
2n
The haploid sperm nucleus may unite with the haploid egg nucleus
resulting in a diploid zygote, and thus the cycle of life begins again.