Dictionary: Bipotential Gonads

Everyone is born with the potential to be either male or female. Everyone is born with both the Wolffian duct (male duct system) and the Mullerian duct (female duct system). What determines maleness is the the presence of the SRY gene. The SRY gene is what allows testis to develop. Once the testis are developed, the male duct system begins to form.When a male is about to be formed, a hormone called the anti-Mullerian duct hormone is released so that the Mullerian duct system which would develop into a female, would be destroyed. Once the Mullerian duct is destroyed, the formation of the testis, including the epididymus, the vas deferns, seminal vesicle and seminiferous tubules can develop. Within females, they too are born with both the Mullerian and Wolffian duct systems. But what is different within females is that the Wolffian duct system begins to decrease when it realizes that the SRY gene is not there to tell it to develop into testis. Thus the Mullerian duct can now develop into the uterus, the fallopian tubes, cervix and parts of the vagina.
There are two part sex determination stages. One stage determines the sex internally and one stage determines the sex externally. When something goes wrong, you could have internal male sex organs but have external female organs, or vice versa. This is why you could have a person with the outer apperance of a female, but internally their organs are male, and they are not able to produce because they do not have a uterus.

Reflections: Sea Urchins

Today in lab we studied the development of sea urchins. In order to understand how sea urchins are developed, we need to understand the stages of animal development. The first stage in development is fertilization. Fertilization is the process in which the sperm and egg fuse together. The next stage is cleavage. This is where the cell will begin to have rapid miotic divisions which will form into a sphere called the bastula. Gastrulation is the next stage of animal development. This is the stage where the three germ layers, ectoderm, mesoderm and endoderm are formed. Each layer is specific to which part of the body will arise. The ectoderm will give rise to the epidermis, the mesoderm will give rise to the muscles and the endoderm will give rise to the dermis. The second to last stage of development is organogensis. This is the process in which organs are formed. The last stage is gametogenesis. Gametogenesis is the formation of gametes.

Within the lab today, we observed the first stage of animal development, fertilization. We first started off the process of fertilization by taking the sea urchins out of the tank and placing them into a basin of sea water for about a minute. Next we placed the  sea urchins upside down within the petri dish and took 2 mL of potassium chloride (KCl) and injected it into the bottom of the sea urchin. We then poured the sea water into a container and turne dthe sea urchins over to observe whether it was a male or a female sea urchin. The male sea urchins gametes were white and the female sea urchin's gametes were yellow. After this was done, we looked at the egg under the microscope and the sperm under the microscope. Next we took the slide with the egg and placed a drop of sperm onto the slide and watched the fertilization process begin. At first the egg sat there for a few seconds then out of no where, the many many sperm came out of no where and quickly rushed to the egg. Within a matter of seconds the fertilization envelope was formed such that there will be a block of any more sperm from fertilizing the egg and creating polyspermy. Here is a picture of the sperm trying to enter through the fertilization envelope that has formed.

I really enjoyed this lab. It was the first time I was able to see fertilization done within that amount of time. Although I was not able to observe the rest of the stages, one day I hope to see the cleavage stage within the gametes of the sea urchins. I think it would be amazing if I was able to see the cell divide into many cells and begin to differentiate. Overall I really enjoyed this lab, I just wish we were able to view the sea urchins through the clevagage and gastrulation stage.

Investigation: The Benefits of Cloning

Today we often hear about the many ethical issues about the topic on cloning. Many of Americans believe that cloning is not ethically correct. They believe that God can only create life and that if we tamper with it then we are playing God. However, many people are not aware of the benefits of cloning. For example as we get older, we tend to lose our brain cells and in some people, they lose their brain cells at a faster pace than others. Alzheimer's is a brain disorder that causes brain cells to be destroyed. For people with Alzheimer's, cloning can serve as a way where the damaged nerve cells can be replaced with embryonic stem cells that were grown to produce nerve cells. The best part of cloning is that, the person does not have to worry about rejection by their immune system. A lot of diseases and problems would be cured if human cloning was allowed.
Another great example where cloning would be useful is in babies with birth defects. If we use cloning we can prevent these infants from having that birth defect. For example if you are an older female who would like to have kids, instead of having the risk of having a child with down syndrome, cloning could be used to prevent the child from having down syndrome by altering that gene.
There are many people today who are in need of different transplants, but the problem with transplants are body rejections and there are long lists of people who are on donor lists. Cloning will solve both problems because the cloned body part will not be rejected because it has the same DNA as the original organism. For example, if a patient is in need of a liver transplant, the likelihood that the liver from a donor will be rejected by the patient is at a higher rate than that of a liver from the patient's stem cell.
As you can see, cloning has many benefits. If only cloning were allowed, many people would be cured of diseases such as Alzheimer's and Parkinson's. Because cloning is not allowed on humans, scientists are not able to test and study the long term pros and cons of inserting stem cells into the body to regenerate specific organs or tissues or cells.