Category Archives: IBDP Biology
Parthenogenesis – Virgin Births in Nature
Happy (belated) Christmas!
How do you really reproduce without sexual reproduction? Asexual reproduction, of course. Simple, really… but not for the females of some species.
There are loads of links in this post, so click on them to learn more.
Parthenogenesis
Some plants, insects, shark and lizard species are known to reproduce by parthenogenesis – embryo development is carried out without fertilisation by a male -so called ‘virgin creations.’
Parthenogenesis can take a range of pathways :
- The egg can be fertilised by a polar body (a ‘leftover’ of egg production), making the chromosome number diploid and triggering embryo development. Here is a simple explanatory animation from amateurmicrography.net.
- Chromosomes in the egg can self-replicate, making up the diploid number and the embryo develops from there.
Other methods include suppression of male genotypes (technically still sexual reproduction?), or eggs cells dividing by meiosis.
The resulting offspring are going to be all the same gender. In some species, the XY system determines gender and parthenogenesis produces all females. In other, the ZW system dictates that they will all be male.
Parthenogenesis is a reproductive strategy that sacrifices the genetic variation (a driving force of evolution) of sexual reproduction for the simple ability to reproduce. Small invertebrates, such as aphids, can use it to produce large numbers of females very quickly.
Komodo Dragons
Larger organisms, such as Komodo dragons (Indonesia link!), have been known to use parthenogenesis in the absence of males, producing an all-male clutch of eggs. It is thought that this might allow them to set up new populations on isolated islands, using just a single female. Here’s a quick video of a Komodo dragon parthenogen hatching:
Some interesting Komodo readers here from Richard Dawkins and Not Exactly Rocket Science.
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Parthenogenesis in sharks
Parthenogenesis has also been observed in captive sharks – the female had no access to males, yet gave birth to live young (though only one, where the normal litter would be larger). Genetic tests confirmed parthenogenesis, rather than the alternative hypothesis of superfecundation (storing sperm for a long period of time). Read the full paper here, and another on hammerheads here. BBC audio explanation here.
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So can it work in us?
Let’s let House MD explain:
In short, no. Not naturally.
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Generally, we use mitosis to replace and repair damaged cells and tissues and for growth and development – filling in the gaps with copied cells. Along the way, our cells differentiate to their function and we end up with a body full of specialised cells – each cell’s structure and biochemistry reflect its function.
We don’t use mitosis for reproduction, as it narrows genetic variation – one of the driving forces of evolution. Instead, when sperm and eggs are produced, meiosis is used – producing daughter cells with half a set of chromosomes. During meiosis, crossing over occurs, giving some recombinants – or ‘mixed up’ chromosomes – leading to some varation. The greatest variation comes from the process of sexual reproduction itself – the gametes – sperm and egg – meet in fertilisation, combining their chromosomes to make a new blastocyst, which becomes an embryo, then a fetus and out pops a baby.
All the offspring of organisms that reproduce sexually carry two copies of each chromosome – one from each parent – and each chromosome carries different alleles – ‘versions’ of each gene. This leads to a great deal of variation and this genetic diversity keeps the the population going.
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What about uses in technology?
Funny you should ask that…
Induced parthenogenesis is being pursued as a method for obtaining embryonic stem cells. Read this New Scientist article to learn more.
The disgraced Korean scientist Hwang Woo-Suk, who shot to infamy after faking stem cell results, was actually and inadvertently pivotal in the use of parthenogenesis as a method to produce human embryonic stem cell lines:
Normally these parthenogenic embryos die after a few days, yet researchers are able to harvest them for stem cells for research. Ethically, these are considered engineered eggs, rather than human embryos. How do you feel about that?
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Questions to think about:
1. How does parthenogenesis differ from binary fission in bacteria, or vegetative reproduction in some plants?
2. How do the XY and ZW gender systems work?
3. How does sexual reproduction lead to genetic variation?
4. What are the costs of parthenogenesis in terms of evolution or resistance to disease?
5. How would the genetic fingerprint of a parthenogen differ from its parent?
6. How would researchers use genetic fingerprinting to determine whether the offspring were parthenogens or were the product of sexual reproduction?
7. What are the ethical considerations of using parthenogenic human ambryonic stem cells?
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References:
Chapman et al. Parthenogenesis in a large-bodied requiem shark, the blacktip <i>Carcharhinus limbatus</i>. Journal of Fish Biology, 2008; 73 (6): 1473 DOI: 10.1111/j.1095-8649.2008.02018.x
Chapman et al. Virgin birth in a hammerhead sharkBiol Lett. 2007 August 22; 3(4): 425–427. Published online 2007 May 22. doi: 10.1098/rsbl.2007.0189.
Digestion: Core and Higher Level
Here is the presentation for the Core section:
Class Notes to fill in here (pdf download – A3 size)
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Some good links:
Enzyme activity animations from McGraw Hill, Northland College and KScience.co.uk
A great animation/tuturial on digestion of different types of foods from kitses.com
And an introduction to absorption(and villi):
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Higher Level Content for the Further Human Physiology topic:
Class Notes to fill in are here (pdf file)
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Some links:
Click4Biology Digestion FHP page
North Harris College animations collection
Gastric secretion animation from McGraw Hill
Digestion of lipids from ZeroBio
Heliobacter pylori and gastric pathology from Johns Hopkins
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Absorption of Digested Foods:
Class Notes to fill in here (pdf download)
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Villi structure from the University of Lanacaster and 3d4 Medical.com
Colorado State has animations for active transport.
Nutrition from JBPub.com has animations for passive transport, fat uptake, facilitated diffusion, endocytosis.
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And, of course, here are JD and Turk to tell us about the diagnostic miracle of egestion:
DNA Structure (Core and AHL)
This is a short one – class presentation is here (click shadowed images for animations and movies):
Here’s a decent video from BBC AS Guru with David Suzuki:
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And here’s a very stylized video of DNA structure from Hybrid Medical Animation. See if you can narrate it:
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The story of the discovery of the double-helix structure is a good example international collaboration and competition, and led to the Nobel prize for Crick, Watson and Wilson (who we never hear about). You’ve got to feel for Rosalind Franklin – her work was key in their discovery and she wasn’t cited for it until after her death.
Here’s a great video, though the presenter sound like he has a mouth full of marbles:
Carbohydrates, Lipids and Proteins
Here’s the class presentation – click the shadowed images for animations.
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For more information on condensation and hydrolysis reactions:
Simple explanation by Terry Brown
Collection of examples from North Harris College
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Carbohydrates:
Explanation and animation from National Louis University
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Proteins:
Life Cycle of a Protein from Sumanas
Making polypeptides from John Kyrk
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Lipids:
Structures of Fats from HHMI
Lipids (and condensation animation) from National Louis University
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Secrets of the Sequence – The Discovery of DNA
This 9-minute clip is an ideal ‘watcher’ to go along with the reader in the Course Companion – it tells the story of the discovery of the DNA double helix structure by Watson and Crick and how their discovery was dependant on the prior work of Rosalind Franklin and the compeitive/cooperative nature of research:
This clip is taken from the vdeo lesson resource provided by Virginia Commonwealth University’s ‘Secrets of the Sequence’ website. They have 50 different videos, each with accompanying lesson plans and activities.
They also have a YouTube channel: VCULifeSciences.
Stem cells used in trachea transplant
Doctors have successfully used stem cells in a rejection-free transplant of a trachea.
This is a great example of internationalism in science – the patient was Colombian, the hospital in Barcelona, stem cells cultivated in Bristol and the final stage of the windpipe construction completed in Milan.
Check your understanding:
Did they grow a new trachea from scratch?
How did they prevent rejection of the tissue?
There is a good short reader on the NewScientist website.
The original research paper was published by The Lancet.
Bio-Alive: a huge resource of animations and videos
Bio-Alive Biology and Life Sciences has a massive set of links to online tutorials, videos, animations, interactives, lectures and games. Huge. Loads.
One of the highlights has to be the video archive of surgical operations!
Follow these links for IB topic help:
Cells: animations – tutorials – virtual labs – lectures
Chemistry of Life: animations – tutorials – lectures
Genetics: animations – tutorials – virtual labs – lectures
Evolution: animations – tutorials – virtual labs – lectures
Or just visit their page for masses of links.
Foldit – help science by playing a game
Foldit is ridiculously addictive. 
It is a protein-folding game/simulation, designed and produced collaboratively between the University of Washington’s Computer Science and Engineering and Biochemistry departments. There is a great introduction to the roles of proteins in metabolism and disease, as well as protein folding, on their about page.
Apart from the great software and in-game tutorials in protein structures, players at the highest level may be contributing to medicine! The University and associated labs are setting problems of protein folding for players to solve – each one an important molecule in its own right and some even the key to curing some diseases.
There is a great article about the game on RichardDawkins.net: ‘Computer game’s high score could earn the Nobel prize in medicine.’ There’s even a classic quote from co-developer Prof. David Baker:
“I imagine that there’s a 12-year-old in Indonesia who can see all this in their head.”
Too right. Let’s represent for Indonesia!
Here’s a quick clip of the game in action at a high level:
Download the game here and get playing!
Mice cloned from frozen bodies
So cloning is nothing new, but for the first time we see healthy lab mice cloned from the cells of dead mice – some articles are calling this a ‘resurrection’, although it is nothing of the sort.
It is, however, a big step forward for genetic reserach – lifting the possibility of cloning long-extinct species out of the realms of pure science fiction and into the ‘almost there’ zone. A team of Japanese researchers from Kobe, Japan, used a modified method to clone these mice from tissues that had been frozen for up to 16 years.
Here’s a clip from Japanese news, with a really clear section showing what looks like the insertion of the nucleus into an egg:
For a useful reader, here is the NewScientist article. Here’s another one from the Guardian.
As ever, one of the best reading sources is the Not Exactly Rocket Science blog, where Ed Yong tackles the research paper directly in his article and makes it easy to understand. Check it out here.
Learning idea: ‘dub’ the Japanese clip into your own language, using the information from the articles above.
How did they achieve it? How does it differ from normal cloning? What surprising results did they encounter?
Try to get your story to complement the images in the video clip.
I can just see Jeff Goldblum‘s gurning face as runs for his life from a cloned dodo…
Interactive Concepts in Biochemistry
Found this useful source on North Harris College’s linklist. 
Wiley.com have produced this online resource for Biochemistry and the Chemistry of Life, and it contains a whole load of interactives and animations.
It is an ideal resource for: photosynthesis, respiration, DNA replication, transcription, translation, cell structure, enzymes and protein synthesis.
i-Biology 
