1. Donna Huffman Biology Lab Instructor Calhoun Community College
Diploid to Haploid
Donna Huffman
Biology Lab Instructor
Calhoun Community College

2. 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 to Haploid.
Each offspring resulting from the combination of haploid sex cells will contain the same chromosome number as their parents.

3. The Big Picture Meiosis Mitosis 2N somatic (body) cells
sex cells (sperm or egg) 2N 2N
2N = Diploid
1N = Haploid 1N 1N 2N 2N 1N 1N 1N 1N 2N
Diploid

4. Diploid vs. Haploid
Diploid (2N) = Full complement of chromosomes found in any somatic cell of an organism
Haploid (1N) = 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)

5. Meiosis Fertilization male female 2N 2N Diploid sex cell production
Haploid 1N 1N 1N 1N 1N 1N 1N 1N 1N 1N 1N 1N
sperm
egg
Diploid Zygote 2N
Fertilization

6. Somatic Cells
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.
Cheek cell nuclei 2N

7. Photomicrograph of Nuclear Chromosomes

8. 2N 1N Meiosis Meiosis in the male and female divides each diploid
cell into 4 haploid sex cells.

9. At what point in Meiosis does the chromosome
number change from Diploid to Haploid?
2N Prophase I
centromere =
1N Anaphase I
1N Telophase II
The homologous pair in Prophase I separates in Anaphase I thus changing the number of the chromosomes from Diploid to Haploid.

10. Female Meiosis: Oogenesis
Oogenesis occurs within the ovary as an immature follicle develops into a mature follicle containing an egg.
mature follicle with egg
immature follicle

11. Female: Diploid to Haploid
Ovary
Egg
Egg producing Follicle 2N 1N

12. 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

13. Male: Diploid to Haploid2N 1N
10X photomicrograph
of testis cross section
Sperm
Testis

14. Conclusion = 2N
1N N
The haploid sperm nucleus may unite with the haploid egg nucleus
resulting in a diploid zygote, and thus the cycle of life begins again.