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 Rabbit1 Cat2 Dog2 Lion3.5 Pig4 Sheep5 Human9 Cow9.5 Horse11 Elephant22

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