Reproduction General Zoology LS2014 11 February 2011 Following Hickman et al. 2011 Integrated...

Reproduction

General Zoology LS201411 February 2011

Following Hickman et al. 2011 Integrated Principles of Zoology, 15th ed., McGraw-Hill, NY.

Ch. 7 pp 134-140, 143-144, 149-150

Donald Winslow

Types of reproduction asexual

binary fission

budding

ameiotic parthenogenesis

sexual

dioecy (separate sexes)

monoecy (hermaphroditism)

meiotic parthenogenesis, haplodiploidy

conjugation

Generalized sexual lifecyclefemale

male

Ovum sperm(gametes, 1N)

meiosis

2N

fertilization

zygote (2N)

embryo

development

Figure 07.1

From Hickman et al. 2006 (13th 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. 2006 (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

Karen Bays in gestation