Homework

Answer both topics and respond to 2 student post:

Topic 1 - Sexual Reproduction

Why do you think that sexual reproduction is considered a pillar of evolutionary advancement? Practically all species (except the most simple) have the ability to reproduce sexually. What do you think are the evolutionary advantages of sexual as opposed to asexual reproduction?

Topic 2 - Meiosis: It's Complicated

Meiosis is a complicated process. When you consider the process of pairing in prophase and the accuracy needed for two cell divisions, you might not be surprised to find that often things do go wrong. In humans, for example, about one third of all pregnancies spontaneously abort in the first two or three months. Most of these aborted embryos have the wrong number of chromosomes. Failure of the chromosomes to separate correctly is called nondisjunction.

Not all failures of meiosis result in early miscarriage. There are late miscarriages and stillbirths of severely malformed fetuses with wrong chromosome numbers. In addition, about one live-born human baby in 200 has the wrong number of chromosomes, often accompanied by severe abnormalities.

One of the most common chromosomal abnormalities is Trisomy 21, or Down's Syndrome resulting from three copies of chromosome 21. This occurs in about one baby in 600. Characteristics of Down syndrome include rounded features, an enlarged tongue that often protrudes, and various internal disorders.

Trisomy 21 occurs more frequently among babies born to women over 35 years old. The age of the father has little or no effect.

What do you think are possible reasons leading to this meiotic nondisjunction in female eggs? It is interesting to note that the total amount of women's eggs are already set by the time she is born, while a man's sperm is continuosly produced. Do you think that there could be some other environmental problems affecting this situation?

Student post 1: Sexual Reproduction

Sexual reproduction will provide variety in the offspring and natural selection, asexual reproduction will produce clones with all the genetic faults that the parent has in the offspring, this is not the case if the offspring are mutated. There are some drawbacks to sexual reproduction though. Sexual reproduction requires two animals or plants while asexual reproduction only requires one so it is far more efficient. Also, asexual reproduction requires less energy too. For the most part, sexual reproduction is often considered superior because without it evolution wouldn't exist.

Student post 2: Sexual vs. Asexual Reproduction

Sexual reproduction allows for a species to interchange resulting in a combination of characteristics while asexual reproduction offers identical offspring without chance of diversity. Evolutionary advancement is built upon the notion that many combinations of a species are created to continually combine traits that will become better over time. With sexual reproduction, a species continues to enhance itself due to the fact that there are endless opportunities for a mix of genes to occur. This one fact alone represents the plethora of capabilities that the species can generate into when allowed to maintain variety as a means of reproduction.

Asexual reproduction can be compared with cloning. The offspring is a replica of the parent and remains unchanged from generation to generation. If two species were to compete through asexual reproduction, the better of that species would jeopardize the other into extinction. The lessor species would need to advance ahead of the better species if they wish to survive.