Thursday, July 15, 2010

Chapter 7

25. Make connections between the following terms:
a. Agouti mice are yellow in color and large, often obese in size. These characteristics cause them to be highly susceptible to cancer and heart disease. As vitamins were supplied to the experimental group of pregnant Agouti mice in a research study at Duke university, thin brown mice who carried the Agouti gene were born. The chemical methyl was attached to the gene and suppressed its expression, otherwise known as DNA methylation. This meant that the environment of the pregnant mice (vitamins) allowed healthier Agouti mice that carried the gene but did not display the characteristics.

b. A certain species of lizard produce offspring that have long or short bodies and tails depending on whether or not the mother smelled a lizard-eating snake during her pregnancy. If so, the offspring will have long bodies and tails to lower their risk of being snake food.

c. The barker hypothesis calls for acquiring a thrifty phenotype. In the case of smoking fathers who had picked up the habit before puberty, the toxins of inhaled smoke are also embedded into male sperm. The sperm signals a difficult environment to the fetus, which means that the sperm creates a child with a metabolism that is sufficient in maintaining energy. A smaller baby results into an overweight child in response to the high calorie, low nutrient Western diet.
d. Maternal inheritance in terms of epigenesis is very direct, in terms of ercieving a particular methyl markup. The egg an that individual developed from was created in their mother’s womb while their mother was still inside that indivudal’s grandmother’s womb. This direct link proves to have epigenetic effects, for if a grandmother smoked, she passed along an epigentic effect to her daughter’s egg supply. That effect caused the grandchildren in the lineage to be more susceptible to asthma.

e. Betel nut chewing is a common cause of oral cancer because it hpermethylates three cancer-fighting genes. These three genes supress tumors, repair DNA, and force lone cancer cells to self-destruct. Because these three genes are hypermethylated by vigorous betel nut chewing, those who feed their habit eventually develop cancer.

26. Epigenesis may be partially responisble for the childhood epidemic of obesity. Explain.

If a mother consumes a lot of junk food, especially during the first critical but unknown weeks of her pregnancy, the embryo receives signals that allude to a nutrient-poor environment in its future. So as certain genes are expressed more than others through epigenesis, the baby is born small, so it needs less food to survive. As a thrifty metabolism settles in, the baby is exposed to foods that are nutritonally poor and calorie rich. This results in fatter children and higher obesity rates.

27. “Good times mean more boys. Tough times mean more girls.” Explain.

Males are more demanding biologically on the mother’s body during pregnancy and are less likely to survive if malnourished. Whether it is the high stress of a tough time that affects how a mother can take care of herself, more boys are miscarried. In fact, male miscarriages had risen to an astronomical increase of 25 percent after the 9/11 terrorist attacks. From an evolutionary prospective, a higher number of females and a few strong males allow for an assured preservation of the human race during tough times than vice versa. Furthermore, after major events such as World War I and II, there was a higher male birth rate.

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