Sexual and Asexual Reproduction

1. U13: Sexual and Asexual
Reproduction
(http://www.spacesciencegroup.org/sootw/graphics/reproduction.jpg)

2. Objectives
At the end of this presentation, you
should be able to:
1. explain the role of mitosis in asexual
reproduction.
2. explain why asexual reproduction
gives rise to genetically identical
offspring.
3. compare sexual and asexual
reproduction.

3. What is Sexual Reproduction?
• If you were told: Define sexual reproduction;
what would you say?
• Perhaps that: “Sexual reproduction is the
formation of offspring from the fusion of
gametes. Fusion is called fertilization.”
Do you remember what process makes these
sex cells or gametes?
• Of course…meiosis.

4. Do you recall what happens in Mitosis and
in Meiosis? Use these diagrams to explain.

5. Meiosis, fertilization and mitosis
• We can show when those processes occur :
Gonad cell  Meiosis  Gametes  Fertilization  Zygote
(Diploid) (Reduction Division) (Haploid) (Haploid + Haploid) (Diploid)
Adult  Mitosis   Embryo  Mitosis 
(Diploid) (Diploid) (Diploid)

6. What is Sexual Reproduction? cont’d
So, you realize that when two haploid sex
cells fuse, a diploid cell is formed.
This diploid cell is a zygote which by
mitosis develops into an embryo in
which the somatic (body) cells are all
diploid.

7. What is Asexual Reproduction?
• If asexual reproduction is the
‘opposite’ of sexual reproduction, then
there should be no gametes, no
fertilization and no need for both male
and female parents to start with.
• Asexual reproduction is the
formation of offspring without the
use of gametes; it involves only
one parent.

8. Methods of asexual reproduction cont’d
• Make a list of as many methods
of asexual reproduction in plants
and animals as you can recall.
• Share your list with your
classmates and teacher before
viewing the next slides 9 - 19.

9. Methods of Asexual reproduction
• Methods include: fission, budding,
regenerating various parts,
forming spores, gemmae and
plantlets, using cuttings, grafting
and cloning.
• Many plants and animals use
these methods of reproduction.

10. Methods of asexual reproduction cont’d
• Many simple animals
and plants use mitosis
to produce new cells
rapidly. This asexual
division is called
binary fission.
The Amoeba demonstrates this beautifully.
www.malebolge.net16.net/science10/amoeba_fission.gif

11. Methods of asexual reproduction cont’d
• Budding is another form of asexual
reproduction resulting from mitosis.
• It is demonstrated below in the Hydra.
Offspring are all
identical to the
parent Hydra
in appearance
and genes.
http://www.saburchill.com/ans02/images2/210807004.jpg

12. Methods of asexual reproduction cont’d
• Many non-vascular plants such as
mosses and the females of some
animals (e.g. wasps, aphids,
sponges, corals, lizards) form
identical offspring asexually by ….
• Parthenogenesis = the development
of an unfertilized egg into an individual.
In organisms that have no sex
chromosomes, a fertilized egg will
develop into a diploid female. A non-
fertilized egg may develop into a
haploid male. http://biology.about.com/b/2007/03/07/what-is-parthenogenesis.htm

13. Asexual reproduction in plants
• Many plants propagate (reproduce)
vegetatively i.e. asexually, relying on
mitosis to form the new plant. Each new
plant has the same DNA as the parent and
is therefore a clone. e.g. On a plantation,
all the banana plants are clones of their
parents.
Look at the following slides to see various
asexual methods used by plants.

14. Many plants
also form buds
which grow by
mitosis to
produce new,
gentically-
identical
offspring.
Examine examples
also displayed
in your classroom.
Asexual reproduction cont’d
http://cccmkc.edu.hk/~kei-kph/Food%20storage%20organ/Food%

15. Methods of asexual reproduction cont’d
Perennating organs e.g. Bulbs and Rhizomes, use
mitosis to produce growth of offspring from buds.
http://www.infovisual.info/01/043_en.html
http://www.hort.cornell.edu/department
/faculty/wmiller/bulb/rhizome.gif

16. Asexual reproduction cont’d
As the new plants grow from buds, they use the
food stored in the perennating organ (Corm)
until they can photosyntheisize for themselves.
Corms
being
harvested.
http://www.hawaiiankingdom.info/C980587838/E20051
218131339/Media/Last%20Roll%20-%2084.jpg

17. Asexual reproduction cont’d
Runners
– buds grow horizontal stems or runners from
which new plants develop.
http://extension.missouri.edu/explore/images/mg0006art07.jpg

18. Artificial asexually
produced plants
In vitro culture – small pieces of
plant material are grown
asexually (through mitotic cell
division) on an agar culture
medium ‘in glass’. When roots
and leaves develop, plants are
transferred to the soil.
Why do we use the term ‘artificial’?
(http://www.saburchill.com/ans02/chapters/chap053.html)

19. Asexually producing animals by
Cloning
• http://bruceleeeowe.files.wordpress.com/2009/11/cloning.gif

20. Comparing sexually and asexually
reproduced offspring
Asexually produced plants
In each picture, the sets of plants, produced asexually are identical to
each other both in appearance (phenotype) and genetic make-up
(genotype). (Picture on left from> http://www.saburchill.com/ans02/chapters/chap052.html
http://topveg.com/wp-
content/uploads/2009/03/strawberry-plants.jpg

21. Watch the short video clips from this websites:
http://videos.howstuffworks.com/hsw/24727-anim
http://videos.howstuffworks.com/hsw/24726-anim

22. Sexually produced plants
These different varieties of apples Flower-colour in the dog-strangling vine
were produced from sexual reproduction. varies because plants have different
Their genetic make-up/genotype differs. genetic make-up.
So, they also look different (colour, shape), http://www.weedscanada.ca/milkweed.html
taste different/are used for different
things (e.g. making juice/cider, eating as
a fruit) because of different genotypes.
http://www.edquest.ca/component/content/article/114/

23. Sexually produced animals
These *penguins look alike These caterpillars are different
but are genetically different, genetically, so also have
e.g. one is male the other variation in colouration.
is female.*(Penguins in the centre) (Both pictures from http://www.saburchill.com)

24. Advantages and/or Benefits
of asexual reproduction
• You should realize by now that each type
of reproduction has advantages and
disadvantages.
Bearing in mind the various methods, can
you deduce the advantages/benefits of
asexual reproduction? Give it a try! Talk
within your group and list at least three.
Now share them with your classmates.

25. Advantages and/or Benefits of asexual
reproduction cont’d
Did you include these in your lists?
1. Time and energy are not wasted in finding a
mate.
1. Because there is continuous reproduction,
large numbers can be produced.
2. Offspring can be produced quickly.
3. Favourable environmental conditions can be
exploited.
4. If parent is of genetic ‘good quality’, the
offspring will also be of ‘good quality’.

26. Disadvantages of asexual
reproduction
• Can you deduce these as well? Give it a
try. Then, Click here for the answer.
(1. Offspring may find it difficult to survive in
a changing environment.
2. If a parent is of ‘poor quality’, the offspring
will also be of ‘poor quality’.
3. Because offspring colonize the same
area as parent, competition and
overcrowding can easily result.)

27. Advantages/Benefits of sexual
reproduction
• Almost all the benefits result from variation.
1.A species that reproduces sexually is able to
adapt to changes in the environment.
2.If the parent is of ‘poor quality’, then the
offspring do not have to be off ‘poor quality’
also because of meiosis and fertilization.
• The third benefit is not due to variation
3. Organisms can colonize a new area easily.

28. Disadvantages of sexual
reproduction
With all the benefits outlined, do you think there
are any disadvantages? What are they?
(Click here for a few to add to those you know.
1.Time and energy are spent to find a mate.
2. Few offspring can be produced especially
because reproduction is not continuous.
3. Because of genetic variation, ‘poor quality’
offspring can result from ‘good quality’ parents.

29. • This genetic variation is beneficial.
• Because each organism of a
population has a different genetic
combination, it means that each
organism has different abilities to
resist changes in the environment.
• These changes could be diseases,
predation etc.
• Variation is the basis for natural
selection which you will learn more
about later.

30. On this slide, note that each sperm has
a different combination of alleles.
http://content.tutorvista.com/science/CBSEXScience/Ch529/images/img1.jpeg

31. Asexual or sexual?
Now that you have explored both,
which do you think is better?
• Website to visit:
http://www.youtube.com/watch?v
=D1_-mQS_FZ0&feature=related