18/10/2010 § 1 Comment
We reached the last lecture of the unit today. Today’s class, we learned mostly about the differences between sexual reproduction and asexual reproduction. Both types of reproduction have their advantages and even some disadvantages—particularly asexual reproduction. But both types of reproduction determine the similarity an organism has to its parents.
Asexual reproduction has its advantages and disadvantages, depending on the circumstances of an organism’s environment. Reproducing asexually means that an organism produces two clones of itself (or just one. In the long run, clones are produced), and these clones are genetically and almost an exact copy of the original organism, the single parent. Only one parent is needed for asexual reproduction. Now, in a stable environment, one that doesn’t change at all and one where parasites, bacteria, and diseases simply exist and don’t adapt to their prey and learn how to penetrate their targets, asexual reproduction survives well. The environment is unchanging, therefore, the asexual organisms live easily because nothing is changing. Asexual reproduction is also very fast and effective and doesn’t take as much energy as sexual reproduction. There are numerous types of asexual reproduction, but the textbook included specific kinds like fragmentation, budding, and binary fission.
Asexual reproduction is good. It’s an efficient process if we take into account the speed, the system of the different types of asexual reproduction and the solidity of copying information and passing it on to generations and generations of organisms. But all of this is reliable in environments that are stable and unchanging. If we take an environment that is unstable and changes all the time, then the asexually reproducing organism may not be able to survive. Most likely, an organism that doesn’t have much genetic variety can die out because its DNA and information is not updated to a point where it knows how to fight parasites, diseases and such. In terms of the computer analogy, I think that asexual organisms haven’t updated their system yet, and are therefore outdated, meaning they’ll die eventually (but this is not true in real life; computers can still keep up even with systems that are a little bit outdated.)
Sexual reproduction is special. The process takes the haploid gametes from two parents (one gamete from each parent) and fuses the gametes to produce one diploid zygote or offspring. Because the offspring has two sets of DNA, (half from mom, half from dad), its own genetic information is unique and new. (Computer system’s been updated). This gives sexually reproductive species an advantage over asexual species in environments that are heterogeneous—always changing. Although sexual reproduction itself takes up more time and energy, the benefits are great. The variety of genetic diversity sex provides a species gives the species more of a chance to survive. Their enemies; parasites, bacteria, infections or diseases, may not have such an “updated system” or won’t have the type of genetic information that tells it how to attack the species. Therefore, the generation of sexual organisms survive the environment and pass on their genes to the next generation.
This advantage and the genetic variety in sexual reproduction is all due to crossing-over during Prophase I early in the process of meiosis and independent assortment and all the factors that make the outcome—the offspring—unique.
There are three kinds of sexual life cycles and involve three different groups of organisms.
Protists undergo haploid life cycles. The organisms in this group include most fungi and some algae. The majority of life in haploid life cycles is spent in as haploidy organisms. Only the zygote begins as a diploid cell and from there, produce haploid cells (through meiosis) immediately. This is the simplest life cycle there is on Earth.
Animals, like humans, go through a diploid life cycle. In contrast to haploid life cycles, the majority of the organisms’ lives are spent in a diploidy phase. Through meiosis, multicellular individuals produce haploid gametes (to later fuse, make diploid zygotes and start the process all over again). These haploid gametes are the only haploid cells during the entire life cycle.
Finally, plants undergo alternation of generations, where the organism switches between being multicellular diploids and haploid individuals. In this phase, sporophytes (which are diploid), divide to produce haploid spores. The haploid spores continue dividing through mitosis to produce multicellular gametophytes. Gametophytes then divide through mitosis again to produce haploid gametes, which fertilize to create a diploid zygote. The zygote divides by mitosis again to produce a multicellular diploid sporophyte. As we can see, organisms that alternate within generations spend a lot of time being haploidy but an equal amount of time being diploidy.
For the essay question, I’m leaning towards answering the second essay question choice: What makes children so different from their parents, and what is the advantage in the difference? Ultimately, I would be discussing meiosis and the effects of crossing-over, independent assortment (and I would take into account both of these factors) and genetic variation within sexual reproduction, in contrast to the lack of genetic variation in asexual reproduction.
I will probably also include why sexual reproduction provides such an advantage over asexual reproduction in heterogeneous environments and use the computer analogies, and other possible analogies from class that I took notes on. The test is this Friday, meaning I have three days to prepare appropriately.