Reproduction and Cloning

Cole Bouchard

Professor Dolby

FSEM: The Human Animal

8 November 2017

Reproducing Clones, Good or Bad?

       The definition of cloning is, “the technique of making an identical copy of something (No Author Atributed). ”In 1885, a German biologist named Hans Adolf Eduard Driesch demonstrated artificial embryo twinning in which was the first demonstration of cloning (No Author Attributed). In 1996 biologists cloned their very first mammal, Dolly the Sheep (No Author Attributed). Cloning started with an embryo, then a mammal. Now, cloning a human has been considered. This idea of reproductive cloning caused a worldwide debate and many questions whether this form of reproduction would be moral. Two categories of reproduction exist: asexual and sexual. In asexual reproduction the offspring acquire their genes and come from just one organism. Sexual reproduction is the form of reproduction in which the parent requires a mate, and the offspring acquires its genes from both organisms. Cloning is a form of asexual reproduction, while sexual reproduction is the natural form of reproduction for humans. Although asexual reproduction has some benefits, sexual reproduction has advantages that are definitely crucial.

       Sexual reproduction is the natural process by which humans reproduce. It allows the offspring to be genetically diverse, and facilitates population levels. Because the offspring come from two parent organisms, they carry more genetic variation. On the other hand, asexual reproduction creates clones of a single parent organism, which generates genetically uniform offspring. Genetic variation is what makes organisms different from one another and is only present in sexually reproducing organisms. Müller’s ratchet is the principle in which a population that reproduces asexually can accumulate multiple deleterious mutations, which can eventually lead to their extinction (Söderberg and Berg 2007). Two circumstances determine the outcome of Müller’s ratchet, and those circumstances are the rate of the ratchet and the size of the population (Söderberg and Berg 2007). The rate of the ratchet would be how fast a species gains deleterious mutations, and the size of the population would determine how fast the mutation propagates (Söderberg and Berg 2007). Müller’s ratchet poses that reproducing asexually increases risk of extinction for that species and disallows diversity among the offspring. “By contrast, sexual reproduction allows most plants and animals to create offspring with good copies of two genes via crossover. That is, if one animal has the deleterious mutation in one gene and the advantageous mutation in another, while another animal has two normal copies of the gene, a mating of these animals can produce offspring with the advantageous mutation and without the deleterious one. Thus, a deleterious mutation coupled with an advantageous one can be undone in organisms with sexual reproduction (No Author Attributed).”

       Organisms that reproduce sexually can eliminate harmful gene through crossover, which is a source of genetic recombination. Organisms that reproduce asexually would pass the harmful gene down to their clone offspring due to their inability to recombine. Potentially if all of the offspring carry the same vulnerability to an environmental threat because they are clones, they all could die.

       Some organisms have the option to reproduce sexually or asexually. For example, an aphid is a small insect that reproduces both asexually and sexually (No Author Attributed). The aphids asexually reproduce most of the time simply because it produces a larger number of offspring in a smaller amount of time. Although aphids usually reproduce asexually, they still reproduce sexually sometimes, but in a specific season when mates are easier to find. Aphids can avoid extinction even though they mostly use asexual reproduction, because their environment is usually stable and therefore, they do not need to change nearly as much either (No Author Attributed). “Organisms that reproduce both sexually and asexually tend to switch to sex under stressful conditions. Mathematical models have revealed that it is much easier for sex to evolve if individuals that are adapted to their environment reproduce asexually and fewer fit individuals reproduce sexually. In this way, well-adapted genotypes are not broken apart by recombination, but poorly adapted genotypes can be recombined to create new combinations in offspring (Otto 2008).” This article relates to the aphids because their environment is stable and they reproduce asexually so their offspring are already fit perfect. If the organisms with poorly adapted genotypes reproduce sexually, then the organisms can recombine and the population can continue to adapt to changes in climate.

       All species need to continue to adapt to their surroundings in order to keep up with competition, and this phenomenon is known as The Red Queen Principle. (No Author Attributed). The Red Queen Principle states that if some organisms continue to adapt to another species and the others do not, then the organisms will have an advantage over the other. “If you take for example the relationship between a parasite and its host. Both the parasite and the host are involved in an arms race with each other. There is pressure on the host to evolve to become resistant to the parasite and there is pressure on the parasite to evolve ways to cope with the resistance of the host. Both species need to change genetically to keep up with the changes in the other species (No Author Attributed).” This is a very basic example of The Red Queen Principle, but it gets the point across that a species needs to adapt to both its environment and to other organisms in order to remain viable. This is another advantage that sexual reproduction has on asexual reproduction. When reproducing sexually, the speed of evolution increases and organisms can keep adapting to give them an edge in the arms race with other species (No Author Attributed).

       Even though reproducing asexually does not allow genetic variation, it still has some advantages. Those advantages include being able to reproduce without mate, reproducing faster, and producing more offspring. Asexual reproduction is a process to reproduce an offspring with a single parent organism. Considering there is only one parent organism, there is no crossover of genetic information to create diverse offspring. The offspring of the parent organism are clones of the parent because they have identical DNA (Scoville 2017). Another key advantage of reproducing asexually is that they can reproduce offspring faster. Asexual reproduction uses a type of cell division called mitosis while sexual reproduction uses meiosis to create sex cells called gametes. Meiosis starts with one single cell which then splits two separate times to create four diverse haploid gamete cells (No Author Attributed). Asexual reproduction uses a process called mitosis to create two identical diploid cells (No Author Attributed). Mitosis is a much shorter process than meiosis. Sexual reproduction also requires a second parent organism which requires time and energy. On the other hand, asexual only requires one parent organism. One final advantage that asexual reproduction has is that it can produce twice as many offspring. Every two asexual organisms can produce four offspring, but with one male and one female, they only reproduce two offspring. “It is a dosage cost, my son only has half of my genes; the other half is from his mother. Only half of my genome is getting into the population. However, if I were an asexual female, my offspring would carry all of my genomes. I would put twice as many genes into the next generation. With asexual reproduction, you get two times as many offspring and two times as many genes into the population (Brown 2001).” Overall, asexual reproduction enables double the offspring to be created in a shorter period of time.

       Essentially, sexual reproduction possesses advantages including producing genetically variable offspring and speeding up evolution. Asexual reproduction also has its advantages, including reproducing without a second parent, reproducing faster, and producing more offspring. Both sexual and asexual reproductions have their disadvantages too. Although asexual reproduction is more efficient and inexpensive, sexual reproduction’s advantages are greater and allow organisms to change and adapt to changing conditions. Rice said, ”And yet, look out the window and almost every organism you see reproduces sexually (Brown 2001).” In order for a population to survive, its individuals need to be able to produce variable offspring. This is exactly what The Red Queen Principle indicates as well. Cloning is a form of asexual reproduction and if humans were to clone instead of having intercourse, then humans could eventually go extinct.

This Video talks about the major advantage while reproducing sexually

Annotated Bibliography

“Aphid.” Aphid – New World Encyclopedia, www.newworldencyclopedia.org/entry/Aphid.

Brown, Gail. “Sexual vs. Asexual Reproduction: Scientists Find Sex Wins.” The UCSB Current, 18 Oct. 2001, www.news.ucsb.edu/2001/011513/sexual-vs-asexual-reproduction- scientists-find-sex-wins.

“Cloning.” Cloning Dictionary Definition | Cloning Defined, www.yourdictionary.com/cloning.

“The History of Cloning.” Learn.Genetics,www.khanacademy.org/science/biology/cellular-molecular-biology/ meiosis/a/phases-of-meiosis.

“Meiosis.” Khan Academy, www.khanacademy.org/science/biology/cellular-molecular-biology/ meiosis/a/phases-of-meiosis.

“Muller’s Ratchet.” Latest Biology and Medical News/Technology, www.bio-medicine.org/ biology-definition/Mullers_ratchet/.

Otto, Sarah P. “Sexual Reproduction and the Evolution of Sex.” Nature News, Nature Publishing Group, www.nature.com/scitable/topicpage/sexual-reproduction-and-the-evolution-of- sex-824.

“Phases of Mitosis.” Khan Academy, www.khanacademy.org/science/biology/cellular-molecular- biology/mitosis/a/phases-of-mitosis.

“Red Queen Principle.” Evolution Biology, evolutionbiology.com/evolutionary-principles/red- queen-principle/.

Scoville, Heather. “What Is the Difference Between Asexual and Sexual Reproduction?” ThoughtCo, 2017, www.thoughtco.com/asexual-vs-sexual-reproduction-1224594

Söderberg, R. Jonas, and Otto G. Berg. “Mutational Interference and the Progression of Muller’s Ratchet When Mutations Have a Broad Range of Deleterious Effects.” Genetics, Copyright © 2007 by the Genetics Society of America, Oct. 2007, www.ncbi.nlm.nih.gov/pmc/articles/PMC2034659/