In the book Survival of the Sickest, Dr. Moalem discusses the system of aging in Chapter 8 page 185. Systemized aging is very common in the eukaryotes that undergo sexual reproductions, and many theories were proposed to explain the relationship between aging (or destined death) and sexual reproduction, and some biologists even study why sexes developed throughout the evolutionary history. One of such theories is Red Queen Hypothesis, which is suggested by Leigh Van Valen; he proposed this theory since he believed that the sexual reproduction occurs to accelerate the mutation rate and thus they can compete against other organisms and increase the chance of survival and reproduction. the prominent example is the parasite that is represented in Chapter 5. They constantly faces the need to reproduce using the host and find the host efficiently. the reason of aging (or death) is also explained using the extension of this theory; since they have to produce greater genetic variety, the older organisms must be replaced with new ones.
These topics are deeply related to the AP BIology's Big Idea #1 (about evolution) and the evolution was throughly discussed through out the course even when the courses are not directly about evolution. From your opinion (or facts), explain the relationship between sexes and evolution, and using some of outside resources, why do you believe that sexual reproduction has some benefits?
Makoto Seita (e-mail: Mseita3@students.d125.org)
The relationship between evolution and the two sexes is that through meiosis, the offsprings result in genetic variation, which in turn causes evolution by natural selection. In meiosis, during prophase 1 in meiosis 1, crossing over occurs from the attachment of homologous pairs of chromosomes, and alleles of the same genes exchange positions. This ultimately results in 4 daughter gametes in the end, all with genetic variation from the other gametes (Campbell 257). The genetic variation of the gametes, by sexual reproduction of the two sexes, results in genotype and phenotype variation of each offspring. Due to the different environmental pressures onto the offsprings with variation, some offsprings will be at a selective advantage, while others will be at a selective disadvantage. Offsprings that are selectively disadvantaged will not survive the pressures, and the selectively favored offsprings will survive (evolution.berkeley.edu).
ReplyDeleteOver a long period of time, the selectively favored offsprings will continue to survive, and their genes will become much more common than those of the selectively disadvantaged. Over a long period of time, this natural selection will cause the offsprings to become much more different than the original species to the point that they are considered to be different species (Campbell 456 - 458). Thus, the relationship between evolution and the two sexes is that sexual reproduction between the two genders causes variation which ultimately causes evolution.
Sexual reproduction is a definite benefit regarding natural selection and increasing chances of survival and reproduction because the variation allows the species to evolve and survive through natural selection, as explained above. Sexual reproduction is also a benefit to preventing extinction of the species because when there is some kind of sudden, unnatural environmental pressure, such as human intervention or sudden disease exposure, species who reproduce by sexual reproduction will be able to survive by variation in offspring, where they will be either selectively advantaged or disadvantaged. However, organisms that reproduce by asexual reproduction will become extinct because there are no genetic variation to survive the sudden environment pressre. This is related to Big Idea #1 (The process of evolution drives the diversity and unity of life) in that sexual reproduction causes the variations that result in evolution, which in turn produces the myriad diversity of life.
Sources:
Campbell Text
http://evolution.berkeley.edu/evolibrary/article/evo_25
Paul Sone (jsone4@students.d125.org)