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 formation
oocyte formation
Meiosis II
A comparison
of meiosis and
mitosis
Mitosis
Maintains
Meiosis
Reduces
1
2
Cells resulting
2
4
Cells involved
Somatic
Germline
Chromosome
number
Nuclear Divisions
And now, Meiotic “Titanic”
Relationship to Gametogenesis
Sperm and Egg
formation
Gametogenesis
• 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
Fertilization
Mitotic Non-disjunction