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