Biological Reproduction

When a man and a woman love each other very much, they will talk to each other about raising a child. When they both are in an agreement they will order one and a stork will come at their doorstep in about nine months. When the stork comes the man and woman become parents, and they raise the baby into a healthy adult. Now that the G-rated version is out of the way, I can discuss the process behind different types of reproduction.

According to the Oxford Dictionary, reproduction is the act of one or more organisms creating offspring, either by sexual or asexual processes. This process is incredibly important for the survival of a species. If a species is unable to reproduce, it cannot create offspring and the population cannot adapt, and ceases to exist after a very short period of time.

Sexual and asexual reproduction are, as you may have guessed, two different forms of reproduction. Asexual reproduction is when an offspring inherits gene traits from only one parent. Organisms such as bacteria and plants use this form. Sexual reproduction, however, is when an offspring inherits gene traits from both parents. Animals from humans, frogs, fish and birds use sexual reproduction.

Sexual and asexual reproduction both have their merits and faults, that is why different species tend to do one or the other, or even both in special circumstances (such as starfish fragmentation). Lets start with the easy one first. The process of a sexual reproduction is a lot quicker than that of sexual reproduction. For instance look at the bacteria. The process behind it is copying its DNA and other parts that are vital for keeping it alive (organelles). When the DNA and organelles have been copied the bacteria can proceed to divide itself. Sexual production takes longer than this, as the DNA has to be split a second time.

So you might be asking yourself, “why don't we all use asexual reproduction?”. If you are this person, sit down and raise your hand next time, you're being a goofball. Sexual reproduction also has it's own benefits.


The benefits to sexual reproduction is probably why so many species use it. By producing offspring sexually then the offspring's genetic information diversifies. For example, here is a Mendelian Table to explain how.


The parents' genes are on the top (father) and to the side (mother). Let us assume that the 'B' represents the gene for skin colour. The uppercase 'B' represents red skin colour and the lowercase 'b' represents white skin colour. The box with the 'BB' is purely red, the box with the 'bb' is purely white. The boxes with the 'Bb', however, now created an offspring with pink skin. Because of this variation the next generation has a better chance of survival, like if there was a hypothetical disease that killed red-skinned and white-skinned organisms, but the pink-skinned organisms remain unharmed. That species has survived through the variation of genes.

The process of sexual reproduction can actually be quite complicated, as different organisms conduct sexual reproduction in different ways. One way is a process called allogamy and the other is called autogamy.


Allogamy is the reproduction process in which we are all familiar with. It is when a male releases sperm cells and fertilizes the female's egg cell. When these two cells combine they form a single zygote. In humans, sperm and egg cells each have 23 chromosomes (which are bundles of DNA). When the zygote is formed it also has the proper amount of chromosomes (46 for humans), assuming there have been no genetic mutations/abnormalities during the process.

Autogamy​

Autogamy is when an organism basically mates with itself. These organisms are usually refereed to as hermaphrodites, which means they have male and female reproductive organs. You may think that this may be a form of asexual reproduction, but on the contrary. Since hermaphrodites have female and male reproductive organs that means sperm cells and egg cells are produced. These cells grow individually, so the genes they carry remain unique from each other.


As stated before, asexual reproduction is a new organism inherits genes from only one parent. Now that we have seen that sexual reproduction is capable of genetic variation, why would some organisms be adapted to using asexual reproduction? Well, it's a lot simpler and quicker. Certain cells are required to reproduce quickly. Think about it, would you mind having your skin cells only coming back once every week rather than the few minutes it usually takes? Also, because bacteria and other prokaryotes reproduce quickly there populations change much more quickly over time, and therefore able to adapt well to their environments.

Fission is the process that occurs in prokaryotes. This is a very simplistic process where the chromosomes (bundles of DNA) begin to grow and divide when the organism is ready to separate. When the organism separates, a genetically identical sister cell is created.


Budding occurs with multicellular organisms, particularly with hydras. What usually happens is on a part of the organism cells begin to rapidly reproduce, which creates an identical copy of the original organism. Once the organism matures it breaks off from the original and begins to grow on its own.


Fragmentation is a type of reproduction that involve an organism being created from a body part of the original. A good example of this is starfish. Starfish do not have a centralized nervous system, so they lack a brain. Instead, their nervous system is spread out across its body. So even if you cut off an arm and the centre of the body isn't totally destroyed, the starfish can regrow it's arms. Even the arm that's been cut off could potentially create a new starfish.


While not technically alive, virus' replicate using a type of asexual reproduction. When a virus attaches itself to a host cell the virus will insert its DNA or RNA which will take over the cell's functioning, which will cause the cell to create more viruses. This is usually referred as the lytic cycle. Sometimes when the virus releases its DNA it will usually take a part off the host cell's DNA and attach itself there. This is useful because the host cell doesn't die and will divide into more cells, ultimately creating more viruses in the long run.

As we finish this lecture, it is becoming more and more apparent that different organisms on Earth are capable of reproducing in different ways. By doing this, it ensures that species are capable of continuing their existence throughout future generations.

Thank you for the class, Fenichi.

It is very informative and you have a well done and interesting introduction and good diagrams.

~Tomb

This was great!

And all this time I just thought something nice happened in the dark, and then you smoked cigarettes.

"Scientist say they have found a way for women to have children without the help of a men. But why?!" -------- Will Rogers (comment made in last show he did in 1935).