Essay on Human Reproduction

2994 Words Oct 15th, 2015 12 Pages
ANIMAL REPRODUCTION &
DEVELOPMENT

Dr Ilma

• The two earthworms in this picture are mating
• Each worm produces both sperm and eggs, which will fertilize
– And in a few weeks, new worms will hatch

Asexual And Sexual Reproduction
• Both occur in the animal kingdom
• Asexual reproduction is the creation of new individuals – Whose genes all come from one parent
• Sexual reproduction is the creation of offspring – By the fusion of male and female gametes to form a zygote

Mechanisms of Asexual Reproduction
• Many invertebrates reproduce asexually by fission – The separation of a parent into two or more individuals of approximately the same size

Mechanisms of Asexual Reproduction
• Budding
– In which two new
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s in patterns of sexual reproduction • Sexual reproduction presents a special problem for certain organisms
– That seldom encounter a mate
• One solution to this problem is hermaphroditism – In which each individual has both male and female reproductive systems

• Another remarkable reproductive pattern is sequential hermaphroditism
– In which an individual reverses its sex during its lifetime Fertilization
• Fertilization depends on mechanisms that help sperm meet eggs of the same species
• The mechanisms of fertilization, the union of egg and sperm
– Play an important part in sexual reproduction External Fertilization
• Some species have external fertilization, in which – Eggs shed by the female are fertilized by sperm in the external environment

Eggs

Internal fertilization
• Other species have internal fertilization, in which
– Sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract
• In either situation, fertilization requires critical timing
– Often mediated by environmental cues, pheromones, and/or courtship behavior
• Internal fertilization
– Requires important behavioral interactions between male and female animals
– Requires compatible copulatory organs

• The embryos of many terrestrial animals
– Develop in eggs that can withstand harsh environments • Instead of secreting a shell around the embryo
– Many animals retain the embryo, which develops inside the

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