Cloning In Plants And Animals

identical_triplets

Clones are abundant in nature – when a zygote splits in two identical twins are formed, when bacteria divideasexually by binary fission the resulting bacteria are clones of the original bacterium, when plants reproduce asexually by producing runners the resulting plants are clones and when a singles cell divides during mitosis the two daughter cells are clones. These clones produced by asecual reproduction are advantageous as the process is quick, can be carried out when sexual reproduction cannot and all of the offspring have the genetic information to allow them to survive in their environment. However, asexual reprodcution generates no genetic variation, unless a mutation occurs, and so all of the offspring are equally suscebtible to envorinomental changes such as the introduction of a new disease-causing pathogen.

There are two main types of cloning – reproductive and non-reproductive. Reproductive cloning is the production of offspring which are genetically identical to either their mother, if created by nuclear transfer, or the other offspring, if created by splitting embryos. Non-reproductive cloning is the use of stem cells in order to generate replacement cells, tissues or organs which may be used to treat particular diseases or conditions in humans.

Splitting embryos is the process of seperating out cells from a developing embryo and so producing separate, genetically identical organisms:

splitting embryos

Nuclear transfer is when the nucleus of a differentiated adult cell is placed in an enucleated egg cell:

nuclear transfer

Advantages of artficially cloning aniamls:

  • High value animals, such as cows with a high milk yield, can be cloned in large numbers.
  • Rare animals can be cloned in order to preserve the species.
  • Genetically modified animals, such as goats which produce spider silk in their milk, can be quickly produced.

Disadvantages of artifically cloning animals:

  • As with asexual reproduction, the genetic unformity of cloning means that all of the offspring will be susceptible to environmental changes.
  • Animal welfare is not always taken into account, for example chickens with a high meat yield, yet are unable to walk, have been produced.
  • It is not yet known if animals cloned using nuclear material from adult cells will develop any long term health problems.

An example of natural vegetative propogation is the English Elm tree. After damage to the parent plant, such as disease or burning, root suckers (basal sprouts) begin to grow from the meristem tissue in the trunk close to the ground, as this is where the lest damage is likely to have occured. This response to stress or trunk death helps the elm to spread, for example, when an elm is felled during copicing, the root suckers grow into a circle of new elms, called a clonal patch, around the old trunk. These new elms produce their own root suckers, and so the clonal patch continues to expand where resources permit it. However, this adaptation can also be disadvantageous, in particular when it is in response to Dutch elm disease. The roots of an elm infected with dutch elm disease will produce many root suckers, but as these suckers are clones of the original plant they have no resistance to the fungal attack and so as they continue to grow they also begin to show symptoms of the disease. Many plants we take for granted also use vegetative propogation as a survival mechanism – potatoes form tubers which are underground stems swollen with nutrients from which new plants grow, onions and daffodils form bulbs which are condensed shoots containing nutrients and from which new bulbs can fom and strawberries have specialised stems, called runners (see below), which grow along the ground, forming new roots and shoots at the tips. These adaptations all mean the plant can reproduce even if it becomes isolated and there is no reliance on wind, insects or other pollinating agents, but the tubers and bulbs are also a disadvantage as they are an attractive foood source for certain animal including us humans.

natural_vegetative_propogation

Plants can also be propogated aritifically. Traditionally there were two methods of doing this; taking cuttings and grafting:

Taking cuttings is where a stem is cut between nodes and its lower leaves are removed. The cut end is then treated with plant hormones to encourage root growth  before planting. The cuttingss are clones of the parent plant. Commercially this techniques is used to quickly produce large numbers of plants such as geraniums.

cuttings

Grafting is where a shoot section of a woody plant, such as a rosebush or fruit tree, is joined to a rootstock (a root and stem already growing). The graft then grows and is a clone of the original plant, but the rootstock is genetically different.

grafting

Although these methods are useful they cannot easily produce high numbers of plants and some plants struggle to reproduce successfully in these ways. The more mordern method of artificial vegetative propogation is micropropogation by callus tissue culture. This method can quickly produce very large stocks of a plant from a small amount of plant tissue, and it has an added advantage that the stock is disease free. Many household plant, such as orchids, are produced using the following method:

  1. A small piece of tissue (an explant) is taken from the shoot tip of a plant.
  2. The explant is placed on a nutrient growth medium and cells in the tissue divide to form a callus (a mass of undifferentiated cells).
  3. Single callus cells are seperated from the mass and placed on a growing medium with plant hormones that encourage shoot growth.
  4. These growing shoots are then transferred to another medium with hormones encouraging root growth.
  5. Growing plants are then transferred to a greenhouse to acclimatise and grow further, before being planted outside.

micropropogation

Plant cloning in agriculture has both advantages and disadvantages. Lots of genetically identical plants can be produced from one plant – you know what the plants will be like and the process is faster than selective breeding. Also, costs are reduced as the crop is all ready at the same time and plants can be produced at any time of the year instead of having to wait until their natural growing season. However, the process is arguably more labour intensive as it’s harder to replant small plants than sow seed. Most importantly, environmental change such as the arrival of a new disease could damage the whole crop as their identical genetics means that they would all be equally susceptible.

Stop Horsing Around!

horses

One of the funniest news stories I’ve heard of late is the so-called ‘disgusting’ revelation that some of Tesco’s beef burgers contain horse meat. And? I for the life of me cannot see any reason to join in people’s outrage! Okay, there is the issue of labelling, in that it probably would have been a good idea to mention on the packaging that the burgers did in fact contain horse meat, but why should we care? Meat is meat, the burgers obviously cooked, looked and tasted like any other standard supermarket burgers otherwise this story would have emerged long ago.

I think the issue here is that some, and by some I am talking about the very small minority of people, do not know where their food actually comes from. Ask a child of about 3 years old where milk comes from and there is a good change their reply will be a shop.

During the Second World War, and many decades beforehand, we were more than happy to chomp away on horse meat, it being one of the few things that didn’t come under rationing. At a time when horses were all around us and used as our main mode of transport it was understood that the animal would be looked after for its working life then when it eventually passed away it would supply a few meals for its owners. 

Nowadays people see a ‘cute’ animal on a menu and automatically refuse to eat it. It’s similar to how funding for conservation works; nobody cares about ‘ugly’ animals or bugs, even though they are vital for the survival of an ecosystem, but say that you want to protect leopard cubs or baby monkeys and you’ll be guaranteed the funds you need. We’ve gone from viewing certain animals as good workers that will provide a good source of food when they die, to adoptive human children that we need to treat as we would a person and stroke and love. Ironically, although we can’t bring ourselves to eat horses, we don’t mind selling our dead horses to the continent where they are more than happy to devour them.

I don’t understand why the issues lies solely with horses though, lambs could be considered cute yet we love eating them on a Sunday with a large helping of mint sauce, we’ll eat rabbit at expensive restaurants yet they’re the sweet little creatures we have as pets.

Everyone just needs accept that animals will die and it is such a waste to not exploit a great natural resource of fur, fat and meat.

Why we should love leeches!

From the Daily Post: Think of something that truly repulses you. Hold that thought until your skin squirms. Now, write a glowing puff piece about its amazing merits.

This post is inspired by my unfourtunate encounters with leaches in the indonesian rainforest which we all grew to despise during our stay, but if you can get over their unpleasant blood-sucking habit, here’s a few reasons they should be admired, even if they can’t be cherished…

– They are widely misunderstood – many people believe their is only species – the blood-sucking one, but in fact they are over 700! In this respect they’re like a little lost puupy just wanting to be loved.

– They are not heartless creatures – they in fact look after their young by building nests, carrying their brood on their bodies, or even carrying them in an internal pouch, the same way marsupials like kangaroos do.

– Doctors were once known as leeches.

– Leeches have been used for thousandss of years as a cure to pretty much any disease, but in modern medicine they have a variety of medical including providing treatments for arthritis, blood-clotting disorders, varicose veins and other circulatory disorders and are also used in modern plastic and reconstructive surgery.

– Not all leeches are attracted to human blood – some are only attracted to specfici animals such as snails and many other small invertebrates.

– Leeches are like fish in that they come in all sorts of colours, shapes and sizes, and so arguably, in their own way, they are beautiful creatures who have mastered the art of camoflage.  

– They are one of the world’s hermaphroditic organisms, meaning they contain both male and female sex organs so can fetilise their own eggs – another example of how they have evolved to survive

– The leech’s segmented body , strong muscular structure and unique pair of suckers are brilliant examples of how evolution and natural selection have created an organism perfectly adapted to its goal.

– It’s fun to move your finger around just out of the leeche’s reach and watch as it follows your finger around with its amazing sense of smell – this game produces the same joy akin to that taunting a cat by pointing a laser around a room and watching it try to catch the dot the laser makes.

– The largest leech ever discovered was 18 inches long – imagine the halloween pranks you could pull if you found a leech that size!

– Leeches or leech shaped and coloured things can be used as bait to catch many types of fish, including trout.

– They are an important part of the aquatic foodchain – invertebrates such asdragonfly or damselfly nymphs and vertebrate predators including fish, amphibians, and waterfowl all count leeches as a regular food source.

– Although most leeches rely on chemo- or mechanoreceptors to hunt their pray, one species, Motobdella montezuma, can track its pray using passive sonar, in that it listens out for vibrations and the system is so sophisticated it can determine the size of the prey so the leech doesn’t attack a too large or too small organism.

– They provide a fantastic metaphor for ex’s who can’t let go as well as other obsessive types.

– If you get bitten by one you should burn it immediately, encase it bites someone else and passes on any diseases in your blood, so you can take pleasure in your revenge!