2 meiosis and gametogenesis chapter 1 thompson and thompson
TRANSCRIPT
2Meiosis 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 ISomatic cells
Germline Cells
Interphase I and Prophase ILeptotene
Prophase IZygotene
Prophase IPachytene
Prophase IDiplotene
Recombination
And on the molecular level
Metaphase I and
anaphase I
Meiosis I is the reduction division
Non-disjunction
Telophase I
Cytokinesis
sperm formation oocyte formation
Meiosis II
A comparison of meiosis and
mitosis
Mitosis Meiosis
Chromosome number
Maintains Reduces
Nuclear Divisions 1 2
Cells resulting 2 4
Cells involved Somatic Germline
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