Fertilization
After Meiosis…
Gonads
• Reproductive organs
– Males have testes
– Females have ovaries
Gametes
• Reproductive cells
– Males have sperm
– Females have eggs
Variation in Offspring
• You receive 23 chromosomes from your
father and 23 chromosomes from your
mother
• Since you are a combination of two
different individuals you are different from
your parents
• This is sexual reproduction – the
combination of two haploid cells (23 in a
human) to produce a diploid cell (zygote
which contains 46 chromosomes)
Sexual Reproduction
• Gametes are produced via meiosis
• The male gamete combines with a
female gamete
• A zygote is produced and develops
into an embryo
• The embryo develops through mitosis
into a mature offspring (gestation
varies from organism to organism)
Fertilization only
occurs if a sperm
meets an egg from
the same species.
Mating Patterns
• Some animals only mate once a year
– Timed so that when offspring are born,
the environmental conditions are
favourable
• Some fish mate only when the tides
are high and during a full or new moon
• Honeybees only mate once in a lifetime
External Fertilization
• External fertilization is when the
gametes met outside of the parents
• Sperm and eggs will dry out, so they
must be kept in a moist environment
• Sperm can only swim in a wet
environment
• Common in fish and amphibians
Internal Fertilization
• Common in most animals that live on land
• Special reproductive structures are
required for this
– Intromittent organ in most birds
– Cloaca
• Sperm is transferred to the female via the
male’s reproductive structure
• Sperm travels inside of the female to reach
the egg
Laying Eggs or Internal Development
• Some mammals will lay eggs and the
foetus will develop outside of the
female
• Other mammals will continue to have
the foetus develop inside of the
female until is has developed into a
mature offspring
• This is called gestation
Gestation of Various Mammals
In Months
Rabbit
1
Cat
2
Dog
2
Lion
3.5
Pig
4
Sheep
5
Human
9
Cow
9.5
Horse
11
Elephant
22
Pros vs. Cons
• List some advantages of internal
fertilization
• List some advantages of external
fertilization
• List some disadvantages of internal
fertilization
• List some disadvantages of external
fertilization
Advantages of Internal Fertilization
• Provides more nutrient investment
into a single egg
• Sexually selected physical traits
• Provides a wet environment for the
sperm and the egg
• Temperature regulation
• Fewer gametes are required to ensure
fertilization occurs
Advantages of External Fertilization
• Requires very little effort as the
sperm and egg can randomly meet
• Female does not have to look after
offspring once they are fertilized
• A specialized structure is not
required to have gametes meet
Disadvantages of Internal
Fertilization
• Complex courtship and mating
behaviours
• Parents (usually female) must care for
the young throughout gestation or
until the eggs hatch
• Specialized structures are required to
ensure the meeting of gametes
Disadvantages of External
Fertilization
• Large number of gametes must be
produced to ensure mature offspring
survive
• Seasonal due to the delicate nature of
the gametes
• Many zygotes are produced but only a
few survive