IGCSE Biology - Sexual and Asexual Reproduction

MAKING SENSE OF SEXUAL AND ASEXUAL REPRODUCTION

IGCSE Biology2.7 Reproduction in humans

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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.


Reproduction

Sexual Asexual


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




http://commons.wikimedia.org/wiki/File:Mikrofoto.de-Hydra_15.jpg

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.


Mitosis• This cell will then divide many times by

mitosis to form the new organism.

Zygote

Embryo

Egg

Sperm


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.


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.


http://mrexham.com/igcse/5-variation-and-selection/5-2-cell-division/

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.


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.


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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IGCSE Biology - Sexual and Asexual Reproduction

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