Donna Huffman Biology Lab Instructor Calhoun Community College Diploid to Haploid 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 to Haploid. Each offspring resulting from the combination of haploid sex cells will contain the same chromosome number as their parents.

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

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)

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

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

Photomicrograph of Nuclear Chromosomes

2N 1N Meiosis 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 = 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.

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

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

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 1N 10X photomicrograph of testis cross section Sperm Testis

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