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. Mitosis The Big Picture somatic (body) cells Meiosis sex cells (sperm or egg) 2N 2N 2N = Diploid 1N = Haploid 1N 2N 1N 2N 1N 1N 1N 1N 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 male sex cell production 2N 1N 1N 1N Haploid 1N 1N female sex cell production 2N Diploid 1N 1N 1N 1N 1N sperm 1N egg 2N Diploid Zygote Fertilization 1N 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 1N 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. immature follicle mature follicle with egg Female: Diploid to Haploid Ovary 2N Egg producing Follicle Egg 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 Testis 1N 10X photomicrograph of testis cross section Sperm Conclusion 1N + 1N = 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.