1. 10/27/08
Lecture 21 – Sexual Reproduction and Meiosis 2
 Human life cycle
 Spermatogensis: The process of sperm generation.
 Meiosis takes place, resulting in 4 haploid cells.
 Differentiation.
 Oogenesis: The process of ova generation.
 Meiosis takes place, resulting in 4 haploid cells.
 Meiosis only takes place for the generation of sex cells; all other cells are generated through mitosis.
 Diplontic life cycle
 There are only 2n cells.
 Haploid cells are gametes.
 Dioecious life cycle
 Sexes are separate.
 Monoecious life cycle
 Both reproductive systems are in a single individual (Hermaphrodite).
 Reciprocal cross fertilization occurs.
 Simultaneously act as both male and female.
 Haplodiplontic life cycle (plants - mosses, ferns, evergreens, flowering plants)
 Meiosis doesn't lead to directly into gametes.
 Meiosis reproduces spores.
 Spores divide by mitosis into haploid structures (gametophte).
 Gametophye turn into gametes.
 Sporophyte: Multicellular diploid phase.
 Haplontic life cycle (plants - fungi, protozoa, and algae)
 Only diploid stage is the zygote.
 Zygote → Meiosis → Haploid
 Protozoan: A member of the Kingdom Protista
 causes Malaria.
 Genetic Variation
 Sexual reproduction (meiosis) leads to genetic variation.
 Reasons leading to genetic variation:
1. Independent assortment of chromosomes during meiosis
2. Crossing over
3. Fertilization event (sperm fusing with ova)