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