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MAKING SENSE OF SEXUAL AND ASEXUAL REPRODUCTION
IGCSE Biology2.7 Reproduction in humans
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Copyright © 2014 Henry Exham
Learning Objectives • Describe the differences between sexual and
asexual reproduction.• Understand that fertilisation involves the
fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo.
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Reproduction
Sexual Asexual
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Asexual reproduction• Cells in one part of the body divide by mitosis
and then break off from the parent to form a new organism.
• All the offspring are genetically identical.• These organisms all reproduce asexually.
Yeast (Fungi) E-coli (Bacteria) Animal (Hydra)
http://commons.wikimedia.org/wiki/User:Dietzel65
Copyright © 2014 Henry Exham
Sexual Reproduction• Sex cells called gametes are produced.• There are two types, a male gamete and
a female.• The male gamete must move to the
female gamete and fuse. • This is called fertilisation.• The new cell formed is called a zygote.
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Mitosis• This cell will then divide many times by
mitosis to form the new organism.
Zygote
Embryo
Egg
Sperm
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Gametes in humans• The male gamete sperm are produced in the
testes.• In the female the ova are produced in the
ovaries.• The cells inside these organs divide by meiosis.• Meiosis produces cells that are not genetically
identical.
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Meiosis• In meiosis four cells are made from the original
cell. • These cells are called haploid cells as they each
have half the compliment of chromosomes.• This process is covered in more detail in
section 5.2 along with mitosis.
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Sperm cell• Sperm cells have a tail for swimming.• The head contains the genes from the father
in the nucleus.• The acrosome digests its way into the egg for
fertilisation.
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Cell division• The whole of asexual reproduction happens using
mitosis. • This is when a cell with 46 chromosomes copies itself to
become two cells with 46 chromosomes.• In sexual reproduction, the gametes are made using
meiosis. • This produces haploid cells with only 23 chromosomes. • Once they combine to make a zygote with 46
chromosomes the new cell can continue dividing using mitosis.
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Sexual and asexual reproduction
Asexual SexualProduces genetically identical organisms
Produces genetically different organisms
Only needs one parent Needs two parents
Uses mitosis Uses meiosis to make gamete and then mitosis to grow in size after fertilisation
Very quick but no variation so susceptible to disease
Slower but produces variation
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This PowerPoint is protected under copyright.It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only.It must not be shared or distributed online in any format.Some images used are under a separate creative commons license, these are clearly marked.
Copyright © 2014 Henry Exham
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