U13: Sexual and Asexual Reproduction

(http://www.spacesciencegroup.org/sootw/graphics/reproduction.jpg)

ObjectivesAt 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.

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.

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

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)

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.

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.

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.

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.

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

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

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

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.

Many plants also form budswhich grow bymitosis to produce new,gentically- identical offspring.

Examine examples also displayedin your classroom.

Asexual reproduction cont’d

http://cccmkc.edu.hk/~kei-kph/Food%20storage%20organ/Food%20storage%20organ_image/potato_stem%20tuber_axillary%20bud.jpg

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.htmlhttp://www.hort.cornell.edu/department/faculty/wmiller/bulb/rhizome.gif

Asexual reproduction cont’dAs 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/E20051218131339/Media/Last%20Roll%20-%2084.jpg

Asexual reproduction cont’d Runners – buds grow horizontal stems or runners from which new plants develop.

http://extension.missouri.edu/explore/images/mg0006art07.jpg

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)

Asexually producing animals by Cloning

• http://bruceleeeowe.files.wordpress.com/2009/11/cloning.gif

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

Watch the short video clips from this websites:

http://videos.howstuffworks.com/hsw/24727-animal-reproduction-the-fertilization-of-an-egg-video.htm

http://videos.howstuffworks.com/hsw/24726-animal-reproduction-the-process-of-meiosis-video.htm

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/

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)

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.

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’.

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.)

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.

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.

• 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.

On this slide, note that each sperm has a different combination of alleles.

http://content.tutorvista.com/science/CBSEXScience/Ch529/images/img1.jpeg

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