Animal Reproduction
Unit 1; Lesson 6 Notes
· All living things die; for a species to survive, it must reproduce
Asexual Reproduction:
· A single parent has offspring that are genetically identical to the parent.
1. Budding – when a part of the parent organism pinches off and forms a new organism
2. Fragmentation – parts of an organism break off and then develop into a new individual that is identical to the original one
3. Regeneration – an organism loses a body part that may develop into an entirely new organism
Sexual Reproduction:
· Offspring are formed when genetic information from more than one parent combines
· Usually requires two parents – a male and a female
· Female parent produces sex cells called eggs
· Male parent produces sex cells called sperm
Fertilization – joining of an egg and sperm
Zygote – when an egg’s nucleus and a sperm’s nucleus join as a fertilized egg, a zygote is created.
Meiosis – eggs and sperm are formed in sex cells of males and females where one cell having 46 chromosomes is divided into 4 cells each with 23 chromosomes
External Fertilization:
· Process where sperm fertilizes the eggs outside the female’s body
Ex. Amphibians and most fish – female frog releases her eggs and a male releases his sperm over the eggs to fertilize them. They usually hatch in about 2 weeks.
Internal Fertilization:
· Process when egg and sperm join inside the female’s body
· Female animal protects the developing egg inside her body
Ex. Reptiles, birds, mammals and some fish
Mammals: all mammals reproduce sexually and nurture their young with milk. Mammals reproduce in one of the following three ways:
1. Monotreme – mammals that lay eggs; young are nourished by milk that oozes from pores on the mothers belly. Ex. Platypus
2. Marsupial – mammals that give birth to partially developed live young; most have pouches where their young continue to develop after birth. Ex. Kangaroo
3. Placental Mammal – nourished inside their mothers body before birth. Ex. humans, bats, armadillos