Fertilization After Meiosis…. Gonads Reproductive organs –Males have testes –Females have...
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Transcript of Fertilization After Meiosis…. Gonads Reproductive organs –Males have testes –Females have...
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