Me Meiosis & Gametogenesis By; AminaBrucaj , Nora Hassan
What is meiosis? • Meiosis is the production of gametes, egg and sperm, through cell division. Gametes are Haploid cells meaning that the cell has one copy of each homologous chromosome. • Meiosis is divided into two cell division: • 1.Meiosis 1- when alike (homologous) pairs split into two cells. First, the homologous chromosomes pair at the metaphase plate and then split as they move to the opposite poles . • 2. Meiosis 2- the replicated sister chromatids split and form chromosomes. (spread across metaphase plate, split at the poles.)
Meiosis 1*GETTING READY* The nuclear envelope and nucleoli are visibly seen. DNA is synthesized.
Meiosis 1*INTERPHASE I * • The nuclear envelope and nucleoli are visibly seen. • DNA is synthesized.
Meiosis 1*Prophase 1 * DNA condensation takes place. The nuclear envelope disappears and the spindle fibers begin to form. The chromosomes become visible as tetrads.
Meiosis 1*METAPHASE 1* • The tetrads line up in the middle. • The spindle fibers are completely formed now.
Meiosis 1*Anaphase 1* The tetrads pull apart and the Chromosomes each with two chromatids move toward the poles.
Meiosis 1*TELEOPHASE 1* *Cytokinesis* The homologous chromosomes each Reach the poles of the cell and nuclear envelopes are formed around them. Each nucleus is now a haploid cell. Cytokinesis follows to produce two Cells.
Meiosis 2*PROPHASE II* -The nuclear envelope deteriorates -Spindle fibers being To grow.
Meiosis 2*METAPHASE II* -Alignment of the chromosomes across the middle of the plate( metaphase) -Attached to the spindle fibers -Single chromosme alignment
Meiosis 2*ANAPHASE II* -The sister chromatids split up into single chromosomes. -Pulled to opposite poles
Meiosis 2*TELOPHASE II* * CYTOKINESIS* • The nuclear envelope develops around • each set of chromosomes. • -Cytokinesis occurs creating 4 haploid • daughter cells • -Haploid= 1 set of chromosomes (23) • each chromosome has 1 chromatid.
Gametogenesis • Gametogenesis is the process of gamete production. Human gametes are formed through the process of meiosis; male gametes are sperm cells and female gametes are the egg cells. • Spermatogenesis • -Creation of the gametes for males, • known as sperm • - 46 single chromosomes are replicated • to form 46 pairs of sister chromatids. • - Through meisois II, 2 daughter cells form • 4 cells each containing 23 single chromosomes • maturing to form 4 haploid sperm cells .
Gametogenesis • Oogenesis • - Formation of haploid cells from an original diploid cell , known as primary ooctye. • - Occurs once a month for females from puberty to menopause. • -Creation of the female gametes, known • as ovaries. • -Leads to the formation of four haploid • egg cells. • -Of the 4 daughter cells produced, 3 are • smaller than the 4th one. • - The smaller daughter cells become known • as polar bodies. • -The larger daughter cell becomes the final • product of oogenesis.