Presentation on theme: "Reproduction General Zoology LS2014 11 February 2011 Following Hickman et al. 2011 Integrated Principles of Zoology, 15 th ed., McGraw-Hill, NY. Ch. 7."— Presentation transcript:
Reproduction General Zoology LS February 2011 Following Hickman et al Integrated Principles of Zoology, 15 th ed., McGraw-Hill, NY. Ch. 7 pp , , Donald Winslow
Generalized sexual lifecycle femal e male Ovum sperm (gametes, 1N) meiosis 2N fertilizatio n zygot e (2N) embryo development
Figure 07.1 From Hickman et al (13 th ed.)
The cost of sexual reproduction Half of all alleles are thrown away during meiosis! Males can’t produce eggs, so why have sons?
From Hickman et al (13th ed.)
The function of sexual recombination Increased variability—new combinations of alleles. Sexual populations better able to adapt to changing environment. (Group selection)
Somatic cells and germ line cells Germ line cells give rise to the gametes. Gametogenesis (spermatogenesis & oogenesis) Oogenesis results in 3 polar bodies for each ovum. Somatic cells give rise to all the tissues of the body.
Mechanisms of sex determination Y chromosomes In humans, presence of Y induces male development. Ratio of X chromosomes to autosomes In Drosophila flies, ratio of X chromosomes to autosomes determines whether male or female. Temperature In reptiles, temperature of nest often determines sex ratio of hatchlings.
Levels of maternal physiological investment Ovipary Development takes place after female deposits egg. Ovovivipary Development takes place within mother’s body, but without nutritional investment from mother. Vivipary Development takes place within mother’s body, with nutritional investment from mother. Example: placental mammals