2 Meiosis and Gametogenesis Chapter 1 Thompson and Thompson

Somatic and Germline cells Development of a fertilized egg into an adult results in two distinct types of cells –Somatic cells These create all tissues and organs of the adult except for cells destined to become sperm or egg They can only undergo mitosis –Germline cells The final differentiated form of these cells are mature gametes: the sperm and egg These cells undergo mitosis until gametogenesis –They then undergo meiosis

Meiosis

Meiosis is required for gametogenesis

Meiosis I Somatic cells Germline Cells

Interphase I and Prophase I Leptotene

Prophase I Zygotene

Prophase I Pachytene

Prophase I Diplotene

Recombination

And on the molecular level

Metaphase I and anaphase I

Meiosis I is the reduction division

Non-disjunction

Telophase I

Cytokinesis sperm formationoocyte formation

Meiosis II

A comparison of meiosis and mitosis MitosisMeiosis Chromosome number MaintainsReduces Nuclear Divisions12 Cells resulting24 Cells involvedSomaticGermline

And now, Meiotic “Titanic”

Relationship to Gametogenesis

Sperm and Egg formation

Gametogenesis

Fertilization Entry of a single sperm into an egg prevents entry of other sperm The DNA of sperm and egg are initially kept separate in “pronuclei” of the zygote Timing of a pregnancy extends from the “last menstrual period” (LMP) rather than the time of fertilization

Mitotic Non-disjunction