Fertilization and Development

Sexual Reproduction The joining of gametes (sperm and egg) The nuclei of sperm and egg fuse This is called fertilization Forms a zygote

Conjugation Sexual reproduction in simple organisms where EXCHANGE of genetic material takes place. Ex: Paramecium, spirogyra, and some bacteria

In Humans Male gamete (sperm) made in the male gonads (testes) Female gamete (egg) made in the female gonads (ovaries)

Hermaphrodites The Earthworm Contains both male and female reproductive organs. Cannot self fertilize Will mate with another earthworm

What is fertilization The joining of male gamete (sperm) with female gamete (egg). The nucleus of these gametes fuse and forms a zygote Sperm (23) + egg(23) = Zygote (46) (n) + (n) = (2n) haploid + haploid = diploid Fertilization

Types of fertilization External Fertilization- Sperm and egg are released into the environment to fuse Internal Fertilization- The fusion of egg and sperm occurs inside the body

The embryo The developing embryo requires food, a stable environment and shelter

External Development On Land- Occurs in birds, reptiles, and few mammals (platypus) A hard shell is required In water- Occurs in fish and amphibians. Fertilized zygote develops in an egg, feeding on the yolk.

Internal Development Fertilization and development of embryo occurs within the mother With placenta- the embryo receives nutrients through the placenta Without placenta- An egg is used to give nutrients to embryo (tropical fish and opossums)

Reproduction in Vertebrates   Fertilization Development # of Eggs Parent Care (Yes or No) Fish Amphibians Reptiles Birds Mammals Chart

Embryonic development Fertilized embryo travels down oviduct Attaches to uterine walls (5-10 days) Embryo starts to divide (mitosis)- 1 becomes 2, becomes 4, and so on until you make a ball of cells called morula. Further mitotic divisions produces a blastula (filled with fluid). 5. The next stage is called gastrula (a ball with 3 germ layers)

The 3 Germ Layers- differentiate Ectoderm- Develops into skin, nervous system, eyes, hair, and teeth Mesoderm- develops into muscles, skeleton, circulatory system, kidney, and gonads Endoderm-develops into digestive and respiratory systems, and liver