Reproduction in Animals
Asexual Reproduction
 Remember, asexual reproduction means = a single living
organism can produce one or many identical individuals
 Examples: Many invertebrates such as sponges and hydra
 Individuals produce buds that develop directly on the parent.
Once mature, they may break off and become independent
Sexual Reproduction
 Remember, sexual reproduction means a male and
female create unique offspring
 Male animals produce male gametes = Spermatozoa
 Female animals produce female gametes = ova
 Gametes = contain half the genetic information
Steps in vertebrate reproduction
1. Male gamete (50%) fuses with a female gamete (50%)
1. This fusion produces the zygote that contains
complete genetic material (100%)
1. The zygote divides and transforms into an embryo
made up of many cells
1. The embryo develops into a small animal
2. When the animal becomes an adult, it will produce
gametes and can also reproduce
For sexual reproduction to be successful…
1. The male and female gametes must be in the same
place at the same time
1. The zygote must obtain the nutrients and protection it
needs to survive. It must also get the warmth and
moisture it needs to develop.
Mating
 During mating, two individuals of an animal species unite
to combine their gametes and achieve fertilization
Fertilization in Animals
Internal and External
Fertilization
 Fertilization occurs when a spermatozoa and ovum of a single
species combine (50% + 50% = 100%)
 Fertilization must take place in a moist environment
 Gametes are fragile cells that die if they dry out
 Moisture keeps egg membrane supple (easy for sperm to enter)
 Sperm can only move in a moist environment
Types of Fertilization
 External Fertilization =
Gametes combine
OUTSIDE the bodies of
both parents
Internal Fertilization = Gametes combine INSIDE
the body – Sperm enter female and migrates
toward the ovum
External Fertilization
 Most aquatic animals reproduce
this way
 Ex. Sea Anemone
 Do not move to find mates
 Release gametes directly
into the water
 Sperm and egg brought
together by sea currents
 Zygotes become LARVAE
that can swim and find food
 Eventually settles on ocean
floor and develops into adult
External Fertilization
 Example: Fish
 Female fish lay eggs in a cluster (many altogether)
 Then the male release his gametes directly onto the eggs
 This is known as SPAWNING
External Fertilization
 Example: Frog
 Similar to in fish – male will
clasp onto female and once she
has laid eggs he releases his
sperm over them
 Frogs (as well as anemones and
fish) do not emerge from eggs
looking like parents
 They undergo several stages of
development first
Internal Fertilization
 Most species of land animals
reproduce this way
 Example: Reptiles
 Cloaca – Opening on both
males and females used in
excretion of waste and sexual
reproduction
 During mating, male and
female join their cloacas and
the male releases sperm into
the female
Internal Fertilization
Oviparous
– lay eggs (ex. Reptiles,
birds, amphibians, fish and insects)
- Zygote is in a liquid environment inside
the shell
- Zygote becomes embryo which will
develop into young animal
- Egg contains all the nutrients needed for
the development
- When development is complete  Hatch
Internal Fertilization
 Example: Mammals
 Male mammals have a PENIS and deposit their sperm inside
the female
 Except for a few exceptions, mammals do not lay eggs
Internal Fertilization - Mammals
 Viviparous – fertilized ovum
completely develops inside the
mother’s body  live birth
 Young develop more completely
this way
 Get nutrients from the mother
 After birth, female provides milk
for her young
Internal Eggs? Say whaaaat?
 Ovoviviparous – females keep their eggs inside
their bodies until they hatch – incubation occurs inside
females body and young are then born live!
Hermaphrodites
 Animals that have both male and female reproductive organs
 Examples: Snails, Worms
 Reproduce by special type of
internal reproduction
 Both inject semen into the
others genital opening and
then both worms lay fertilized eggs
Memory Check
 Complete the memory check on page 256 of your
textbook