Writing in Biology

Probability is the chance of an event occuring. In genetics, probability plays a significant role during crosses to predict outcomes. In class, students looked at an example where a female gray cat mates with a gray male cat. The black coat color is dominant over the gray coat color in the cross. The parents produce a gray female kitten in a litter of six kittens, what is the probability that there are three blacks kittens and three gray kittens? We know that the mother is black and she must be heterozygous because they produce a kitten that is gray. In order to find the probability of three black kittens and three gray kittens, we have to use the binomial expansion for n=6 and then the equation 20p3q3. Once all the values are plugged into the equation, the chi-square will calculate the goodness of fit. The null hypothesis can then be accepted or rejected based on the probability outcome.

The genetics of dog hair colour is much more complicated than most people might think. There are many different genes, each themselves with sometimes three or four alleles, whose combination leads to the hundreds if not thousands of different coat varieties seen in canids both domestic and wild. Many people tend to think of genetics as working in the traditional Mendelian fashion of basic dominance and recessiveness of genes controlled by a single allele (say A/a), but dog hair colour is one of many examples where the answer is not that simple. The introduction of more than two alleles whose dominance over one another varies leads to many more possible combinations of traits and is why the pattern, colour, length and curliness of dog hair varies so widely across the family Canidae. One gene that plays a key role in coat colour is the agouti gene that encodes for a signalling molecule which disrupts the pathway in fur melanocytes (specialized pigment-producing cells) that leads to eumelanin production, these being darker brown and black pigment molecules. As a result, dogs that express the aguoti gene at high levels instead produce lighter phaeomelanin pigments that result in yellow, gold and even red coat colours. It's still not that simple however because the agouti gene has four alleles (a, a^w ,a^t , a^y ) each leading to varying levels of expression and different patterns of light and dark colours seen across the Canidae family.

There are 8 different types of blood. These types of blood are classifed by the receptors found on their plasma membranes. Red blood cells can have 3 different receptors: A, B, and/or Rh. Different blood types are very specific in reconizing "self" from foriegn substances. Blood types that do not contain a specific type of receptor have antibodies against those receptors. If another type of blood was transfused, the antibodies would attack the foriegn blood. Blood type O- is the universal donor because it lacks all receptors, while blood type AB+ can only donate to AB+ blood. However, AB+ blood can recieve blood from all other types of blood because it does not have any antibodies.  Blood types that have antibodies against a certain type of receptor cannot recive blood from a blood type with that receptor. Likewise, blood that has certain receptors cannot donate to blood that has antibodies against that type of receptor. 

Protein being one of our major food groups in our health plate is also a very controversial topic when determining what is good or not good for the human body. There are different sources of protein such as meats, fish, nuts, beans/lentils, cheese and poultry. Red meat is said to be high in saturated fat and is classified as a Group 1 carcinogen by the World Health Organization. A carcinogen is a substance that has the ability to cause cancer in living tissue, meaning that humans should limit the amount of red meat eaten a week. Although these meats such as lamb, beef and pork are 'probable' causes of cancer, they dont indicate the risk of getting cancer. There are benefits however to eating lean red meat such as vitamin B12, zinc and iron. Red meat is not only classified as being a probable cause of cancer, but it is also a leading cause of heart disease. In the states, cardiovascular disease is the number one leading cause of death. Many Americans should consider limiting the amount of red meat they eat and substitute it with a variety of other protein dense and vitamin dense foods such as tofu, fish and beans/lentils. A variety of vegetables also have a high content of protein and fiber such as broccoli, cauliflower, spinach and brussel sprouts.

The interspecific interaction I will be documenting is between humans and grass.  Despite the fact that there are an abundance of paved sidewalks on campus, students still feel the need to walk over the grass in very specific patterns.  This leads to the grass being matted down and even uprooted, leaving distinct dirt paths cutting through otherwise grassy fields. A good example of this is a position just north of the student union and just east of the parking garage.  Just looking at a map, one can tell that the humans benefit because they save time. However, the grass does seem to have one mechanism of defense. If it is saturated with water, it will be muddy, and humans will be less inclined to trample it because doing so would damage their shoes.

In 1995, Minnesota middle school students sampled frogs in a nearby pond and found that half of them were deformed, and it  was discovered soon after that this was a widespread occurrence. A total of 8 frog and toad species were affected by this. Approximately 0.2% of frogs found in the area were deformed from 1973 to 1993, and that percentage increased to 2.3% by 1996. The cause of this deformity was found to be a species of trematode, Ribeiroia ondatrae, which are flatworm parasites that cause deformities and sometimes death in frogs. Trematode larvae in frogs cause cysts. If the cysts are in a developing tissue, it can cause a deformity; for example, if the cysts are found in a tissue that is developing legs, the cysts can cause extra or truncated legs. The occurrence of deformities in the frogs in the area had increased due to runoff of Atrazine, an herbicide (which is banned in the European Union and other developed countries) which kills plants in a pond, causing them to decompose and ultimately cause eutrophication of the pond. This eutrophication of ponds led to more snails in which trematodes begin their lives. The trematodes then move from the snails into the frogs, causing the deformities.

In order to determine the power of an experiment, the experiment must be conducted several times. If the experiment is successful or shows similar results the majority of the time, the experiment would have a great power. Initially, before conducting an experiment several or dozens of times, the initial experiment must be well thought out. An experiment should have a high (if cost is an issue, then reasonable) amount of replicants. All experiments will have an experimental noise which will cause variation, but if there is an alarming amount of variation in the initial experiment, there is something wrong with the experimental design, there could be another variable interfering in the experiment which isn’t realized, etc. A simple experimental design has more power than a very complex one. The P-value cutoff should be around 0.05, meaning that the majority of the time, the experiment is accurate and the results are more easily proven. Finally, an experiment which shows a strong treatment effect will have greater power than an experiment which does not. 

Jasmonic Acid is the hormone released in plants when they experience damage from herbivores in order to induce defenses. Although damage to plants often results in fewer or less attractive flowers or fruits, recent work has shown that jasmonic acid also induces nectar productions in some systems. When a caterpillar eats a part of a leaf, the plant will produce jasmonic acid to repair itself after the tissue is lost. Simply cutting a leaf will not induce jasmonic acid production because there is an enzyme in the saliva of the caterpillar which induces the production of jasmonic acid. However, spraying jasmonic acid on the plant will increase the production of jasmonic acid, but will not affect the tissue negatively. 

Giving-up density is a theory where animals will leave a place they can feed when the costs of staying in the area are higher than the benefits. An observational study that could be done to measure this is placing 10 feeding stations for a small animal with many predators, perhaps a bird feeding station, in the middle of meadows where predators can easily spot them, and place 10 feeding stations near shrubs. After an appropriate amount of time, measure the amount of food left at each of the stations to see what the giving-up density for birds in that area is. 

It was found in an observational study that women taking hormone replace therapy for treating menopause had a lower than average incidence of coronary heart disease. This belief led to an experiment in which women were randomly assigned hormone replacement therapy. But what was found in the experiment was that women randomly assigned to hormone replacement therapy actually had an increased rate of heart disease. The reason the women from the first study had a lower incidence of heart disease was because they were from a higher socioeconomic status and therefore had access to better health care.