To anyone who accepts Darwin’s theory of natural selection, evolution of sexual reproduction is one of the most puzzling issues. Faster evolution through increasing diversity of genotypes is the obvious long-term advantage of sexual reproduction, but it would seem that the short-term advantages of parthogenesis are so great that ‘sexual’ species would be driven to extinction before the long-term benefits could have an effect.

Parthenogenesis has been observed in dozens of species such as birds, amphibians, insects and fish. This asexual reproduction occurs when an egg cell is triggered to develop as an embryo without the addition of any genetic material from a male sperm cell. Occasionally scientists do find a parthogenetic clone competing with its ancestral sexual species. Usually the clone is found to be steadily outcompeting the ancestral species without strong selective pressure. So why have sexual species survived and prospered?

To give a simplified example, consider a lake populated by a million fish of one species that lives for only one year, and in which fathers do not help raise offspring. Every year, half the fish (the females) lay eggs. For the population to be stable, on average two eggs from each female must be fertilized and successfully reach adulthood.

Now suppose one egg is a mutant. It survives and becomes an adult parthogenetic female. There is no reason to believe that the survival rate of this female’s eggs will be different, so next year there will be two parthogenetic females, genetically identical to their mother, or in other words the beginning of a clone.

Just to keep the arithmetic simple, let us make the unlikely assumption that the lake expands just quickly enough to keep the number of sexually reproducing fish constant at one million. Under these circumstances, the number of parthogenetic fish will double every year. After about twenty years, there will be one million parthogenetic fish, the same as the number of sexual fish.

To continue our arithmetically simplifying assumptions, let the lake shrink at just the rate required to increase competition to the point that on average only one egg from each female fish survives. Now the number of parthogenetic fish will stay constant, but the number of sexual fish will be cut in half every year, until after another twenty years there is only one sexual fish and the lake has returned to its original size. At this point, the sexual species is doomed.

If the size of the lake remained constant, or changed randomly, the proportion of parthogenetic fish would be the same, and so the same result would be achieved. For a larger population, more generations would be needed to eliminate sex, but this analysis would seem to indicate that all sexual species are doomed within a few hundred generations of a viable parthogenetic mutant appearing. Yet sexual reproduction has continued to thrive for at least two billion years. Some other factor must be present.

In our above example, sexual reproduction would seem to disappear after forty years. Whatever factor causes sex to survive must efficiently destroy clones. What factor can be so powerful?

One of the factors that can eliminate clones with such efficiency is disease. That is when the sexual reproduction and associated with it diversity helps population to survive. Let us focus on a disease caused by deadly bacteria. Bacteria divide (parthogenetically, by the way) two or three times an hour, so during the course of a year, or one fish generation, these bacteria would duplicate 25,000 times. Each time a bacterium divides, it introduces DNA mutations because bacteria copy their DNA less accurately than higher organisms.

While the bacteria are infecting a single fish, most mutations will be disadvantageous (i.e. the mutated bacterium will either fail to reproduce, or will reproduce more slowly) but there will be an occasional beneficial mutation that will actually speed up reproduction in the specific environment of that individual fish. If it takes a month for an infection to kill a fish, that is approximately 2,000 bacterial generations. If there is a beneficial mutation every 200 generations, then by the time the fish dies, the most rapidly reproducing bacteria will have accumulated ten mutations helping them prosper in that particular fish.

To outlast the individual fish, the bacteria must have the capability of leaving that individual and infecting another. In a sexual species, the bacterium with ten mutations will find itself in a genetically different fish, in which the very mutations that helped it in its prior home may now be an impediment to survival and reproduction. Before the bacteria manage to shed these mutations and adjust themselves to this new environment, the fish’s immune system may destroy them. If both fish are members of the same clone, on the other hand, the bacterium entering the new fish will find itself in exactly the same environment as it previously prospered in, and should have no difficulty in multiplying rapidly and ultimately killing this fish.

The more numerous the clone becomes, the higher the concentration of bacteria specifically bred to infect and destroy them. It seems almost inevitable that the clone will be completely eliminated well within the 40 years (one million bacterial generations) that it would otherwise take for the clone to destroy the ancestral sexual species.

Problem solved. Sex is here to stay. Perhaps, we should be grateful to bacteria and pathogens for having pleasures of sex and for love in general!

Even though Charles Darvin titled his famous book ‘The Origin of Species’, he considered the mechanism of new species’ origin a great mystery. Even now, one of the greatest mysteries of biology is how two groups of animals become genetically incompatible. It is possible to imagine that two groups of animals become separated in space and lose the ability to breed with each other for a long time, gradually adapt to different environmental factors until they lose physical ability to mate even living at the same territory. Development of new species without physical isolation is much more difficult to explain because of free exchange of genetic information between individuals. Even more difficult to comprehend is the fact that changing only one gene may be sufficient to create new biological species.

A gene called Prdm6 was found long time ago as a gene involved in recombination, the process of crossing chromosomes and exchanging DNA regions between paternal and maternal chromosomes in the gonads. The process takes place only during maturation of reproductive cells – spermatozoids and oocytes. The DNA shuffling is the reason why each organism is unique. So far, DNA recombination was not associated with the creation of new species. Scientists found that the protein Prdm6 has several so-called Zn-fingers that are encoded by short DNA repeats called satellite DNA. As satellite DNA is located in hot-spots of DNA recombination, it is frequently mutated and repaired. As the result, Prdm6 protein gets more or less repeats of its Zn-fingers. It appears that the chromosomes that have different variants of the gene cannot properly pair and exchange genetic information during gametogenesis. All animal species have homologous Prdm6 genes. Certain lines of laboratory mice that express different variants of Prdm6 protein cannot produce fertile offspring. Scientists found that different populations of humans also produce Prdm6 proteins with different number of Zn-fingers. It is conceivable that people with certain variants of Prdm6 proteins may not produce fertile children and may develop into a new human species. This process will require selective pressure, either natural or artificial, and many years to develop true new Homo species.

Objective:
Explain the processes involved in cloning and producing transgenic animals

Genetic modification
Genetic modification is the change of the genes of a living organism such as a plant or animal using modern techniques of biotechnology. DNA sequencing of entire genomes has been instrumental in the development of new genetically modified animals.

Purpose of genetic modification of animals
The main purposes of using genetic modification of animals are:

improving food-producing animals and agricultural plants
Development of new of plants and animals through natural selection and evolution is a slow process that takes millions of years. Ancient people learned to improve the speed through artificial selection. As the demand for food increases with world’s population growing, genetic modification of animals and plants became the most efficient way of increasing agricultural production. Genetically modified animals and plants developed in a matter of a few decades produce more and better milk, meat, fiber, they became more resistant to diseases and droughts.

development of treatments for human disease
With genetic modification of animals, production of certain important human proteins such as insulin has become a reality. Scientists have seen success with the use of some animal tissues, bones, and joints in humans. Research continues in the field of skin and organ tissue transplantations. Pigs are commonly used in this research because of their similarities to humans. Pigs producing ‘humanized’ skin, for example, can be used as a source for skin restoration in humans. Animals such as mice are genetically modified to help understanding and developing treatments for human and animal diseases.

production of pharmaceuticals
Genetic engineering has allowed production of certain hormones (insulin, human growth hormone, bovine and porcine somatotropin and other). Current research has shown the possibility of genetically modifying sheep or cattle to produce human proteins in their milk.

Benefits
Genetic modification of animals has shown several benefits. These include increased resistance to disease and parasites, increased productivity and improved hardiness to weather factors. Other benefits involve animal products, such as increased yields of meat, eggs, and milk.

Cloning animals
There are two main types of animal cloning: reproductive cloning and cloning through recombinant DNA technology

Reproductive cloning is a common process very well known for creating an exact genetic match of an animal. In 1996, Dolly the sheep was produced by reproductive cloning and was the first animal to be cloned from adult DNA. Since Dolly, advancements have been made in the process of cloning, and several other animals have been cloned. The reproductive cloning process begins with the transfer of genetic material from the nucleus of a donor adult cell to an egg whose nucleus has been removed. The egg is stimulated with chemicals or electrical current to promote cell division. As the cloned embryo divides in a test tube and reaches a suitable developmental stage, it is transplanted into a female host. The female carries the cloned embryo until birth.

Recombinant DNA (rDNA) technology is the process that occurs when fragments of DNA from two different species are joined in vitro to form a single DNA molecule. Usually, the DNA from one species is incorporated in a plasmid that is a circular DNA replicating independently on the bacterial genomic DNA. A plasmid is then amplified inside the bacteria, isolated and inserted into the genome of embryonic stem (ES) cells to be altered, allowing the DNA of two different organisms to be combined in a single cell. Then the cell is injected into an embryo at early stage of development and the embryo is then implanted in foster mother uterus to produce a chimeric transgenic animal.

Transgenic animals
A transgenic animal is an animal that has incorporated a foreign gene into its cells. The animal can pass this transgene (altered gene) on to its offspring. Every cell within the transgenic animal contains a copy of this transgene. Several different methods can be used to produce transgenic animals.

Microinjection is the most common technique used to produce transgenic animals. Injecting DNA into a cell using a fine-diameter glass needle and a microscope constitutes microinjection. During this operation, the chosen gene from the same or a different species is directly microinjected into the ovum. The injected DNA integrates randomly with nuclear DNA and its expression is possible only when the foreign DNA is attached to a suitable promoter DNA sequence. There are many examples where different types of animal cells have been microinjected and successfully transferred.

Once a manipulated fertilized ovum develops to a specific embryonic phase, it is transferred to the oviduct of a recipient female. The embryo will develop just as a normal embryo and is typically carried full term.

Marker gene is a gene that helps easily identify animals which successfully incorporated transgene. With the use of marker genes, it is possible not only to determine whether a transgenic animal has received the desired DNA but also whether the genes in the DNA are being expressed. The genetic markers help identifying the location of incorporated DNA in the host genome. The expression of a marker gene can be visualised with staining selected tissues or whole embryos. Polymerase chain reaction (PCR) followed by gel electrophoresis is a technique of choice due to its speed and sensitivity.

Improving domestic animals
Currently the U.S. Meat Animal Research Center (USMARC) has developed DNA markers to identify all cattle in the United States. This method allows improved animal traceability and verification of disease sources. DNA testing also allows producers to base their management and selection process on genetic potential of identified animals.

DNA testing can determine the presence of certain traits and proteins. A common method used in the beef cattle industry involves the presence of the tenderness or marbling genes. This information allows producers to enhance the production of tender meat and meat with optimal marbling. It also allows producers to produce a consistent product.

Xenotransplantation
Xenotransplantation is the transfer of living cells, tissues, or whole organs from one species to another. People who need a kidney for transplantation often chose to use a pig kidney even if that organ was obtained from a genetically engineered pig.

Summary:
With the new technology of genome sequencing and mapping, genetic modification holds the potential for improvements in livestock. The main purposes for using genetic modification of animals are increased production of food-producing animals, treatments for human disease, and production of pharmaceuticals.

Did you know?
1. Identical twins are clones that occurred naturally.
2. Many animal cloning technologies are used for clinical reproductive procedures.
3. The process of cloning in the lab is a very complex procedure.

Checking what you have learned
1. What are the main purposes of genetic modification in animals?
2. What is a transgenic animal?
3. What are the steps involved in cloning an animal through reproductive cloning?
4. What are the steps involved in producing a transgenic animal?
5. How are marker genes used?

Most people would offer help to a friend in need. Is altruism unique to humans or is it a common trend in other animals? A new study describes altruistic behavior in rats and finds rats empathetic to each other.

In the study, rats were allowed to live in one cage to get used to each other, then one of the rats was placed in a narrow clear plastic tube with a small door that could be opened only from outside. The second rat could see the trapped pall and hear its unhappy calls for help. The free rat immediately starts sniffing the trap, biting it, climbing on it making clear it wants to get the trapped rat out. Once the free rat saw the tail of trapped rat poking through the holes in the trap and grabbed the tail and pulled on it trying to get the pal out. Eventually, the free rat would accidentally push the button and open the trap door releasing its buddy. The researches repeated this experiment many times. The free rat would quickly learn to open the trap door on purpose but only did it for pal and not if the trap was empty or contained a toy rat. They did it even when opening the door released their pal into a separate cage. So it was not just that the free rat wanted a playmate. The free rats seemed to just want to help. The results are reported in the journal Science.

Why rats do that? Scientists could not simply ask rats. All they can do is to design experiments to get as clear and as easy to interpret answer as possible. Rats really care about food and they love chocolate. So scientists put two traps inside the plastic box. Inside one trap, they put chocolate and inside the other – distressed rat. The free rat quickly opens both traps in no particular order. What it tells scientists is that liberating a trapped friend has the same value to free rat as getting chocolate. Even though the free rat could have just gobbled the chocolate first and then release the pal, it instead chooses to share the chocolate with fellow rats.

People often think that these social abilities such as compassion and altruism are unique to humans and apes as if they just appeared without preceding evolutionary events. This new study is a dramatic confirmation that not only humans can feel pain of friends and try to help. It looks like the roots of empathy and altruism go way back. This study gives scientists a new tool to look in depth of the phenomenon of empathy, altruism, love and abstract thinking in general.

It appears that altruism was not an accident, it was rather evolutionary beneficial. Human evolution has proven that it is easier to survive living in larger communities helping each other and sharing food and resources. Those who did not fill helping each other did not survive at harder times and did not pass their genes to future generations. That is how genes of altruism have been accumulated and fixed in human populations. That is how altruism became a norm of humane behavior.

All living species on Earth, even microscopic viruses compete with each other for space and resources in order to survive and reproduce. Some viruses are exceptionally aggressive in expanding and using resources so that they cease to exist because they consume all resources. The “virus” Homo sapience is not an exception. It leaves fewer and fewer places on the planet for wild flora and fauna. Larger organisms are especially vulnerable to the ferocious “virus” Homo sapience. Smaller organisms are more lucky and have more chances to avoid the lethal weapons of cunning biped predators. Life on the planet becomes smaller in size…

About 25,000 years ago, Homo sapience began to actively explore and occupy the planet and use its resources. Humans destroyed about half of all terrestrial species of mammals weighting over 45 pounds. Mammoths, mastodons, saber-toothed tigers, giant sloths, beavers, as well as many other representatives of mega fauna became extinct as the result of direct and indirect actions of humans.

Anthony Barnosky, an ecologist at the University of California at Berkeley, says that most species of large mammals disappeared during the time interval of 4000 years, which ended about 11,000 years ago. During that period, Australia has lost 88% of the species diversity of large mammals, South America – 83%, North America – 72%. Africa and Eurasia lost only one in five and a one in three species of large mammals respectively.

P.S. Jared Diamond in his book target=”_blank”"Guns, Germs and Steel. The fate of human societies” explained this latest animal extinction by the fact that people inhabited Australia and the Americas relatively recently and already possessed developed weapons and hunting techniques. Animals simply were not ready for the sudden appearance of a new predator. As opposed to Australia and Americas, humans were present in Africa and Eurasia for a very long time and had much more time to gradually adopt the modernization of weapons of Homo sapience.

The world, as we know it, will change. This is inevitable. There are only two simple choices that are available to all biological species at harder times: either change or die. Humans as a biological species face the very same choice. The change is going to be either biological or technological. It is possible to slow harsh natural selection, as we just did through science and technology, but genetic changes are accumulating in the population in the background and one day will reveal themselves in an ugly way. As we are canceling natural selection, human population becomes more and more diverse, meaning sick and weak. Natural selection has to be replaced with artificial selection and use of intelligent approaches to improve the genetics of Homo sapience. We will also learn to use different sources of energy and use different habitats to live. All these changes are noticeable even today.