Un-shelling Your Breakfast

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Zoo InternQuest is a seven-week career exploration program for San Diego County high school juniors and seniors. Students have the unique opportunity to meet professionals working for the San Diego Zoo, Safari Park, and Institute for Conservation Research, learn about their jobs and then blog about their experience online. Follow their adventures here on the Zoo’s Website!

libby_week4_picHow do you like your eggs? Sunny side up, scrambled, or over easy? I always break the yolks when I try to flip my eggs, so I’ll stick with scrambled for now. Eggs are a delicious source of protein no matter what way you cook them. But, what is an egg? Zoo InternQuest found out the answer to that question at the San Diego Zoo Institute for Conservation Research. Dr. Thomas Jensen, a scientist in the Reproduction Physiology Department, explained to us that an egg, like the ones you get at the grocery store, is an oocyte. 

You may be thinking, but isn’t an egg a baby chick? Well, the answer is yes and no. An oocyte is really only half a chick. Until the egg is fertilized, it is the reproductive cell of the hen. If it is fertilized, it becomes an embryo and later, if it is incubated under the right conditions, a chick. If it isn’t fertilized, then it stays an oocyte and becomes an egg you can buy for breakfast.

The egg is put together inside the hen before she lays it. There are three main parts to an egg: the yolk, the whites, and the shell. As Dr. Jensen explained, the yellow yolk in the center of the egg serves as a chick’s lunchbox. The yolk has all sorts of proteins and fats to feed the growing chick. When the egg isn’t fertilized, the yolk is a wonderful source of protein for the people who enjoy eating it. The egg whites consist of the liquid outside the yolk. The egg whites mainly serve to protect the chick from any movement that could harm it. It’s a layer of bubble wrap around the yolk that will absorb any shock the egg receives. The egg whites also have protein like the yolk and provide extra nutrients to the growing embryo. They are like the extra snack you packed for after lunch when you get a little bit hungry.

The last part of the egg that is put on is the shell. It’s what gives the egg its color and shape. Contrary to popular belief, the color of the shell has nothing to do with the nutritional value of the egg. A white egg is just as good for as a brown egg. The color of the shell is determined by what proteins the hen puts into it. So, if the egg is white or brown or blue, it’s all the same nutrition for you. At the Institute for Conservation Research, we saw many different kinds of eggs; big and small, colorful and plain. We got to hold the egg of a kiwi, a small brown bird from New Zealand. The kiwi’s egg is 20% of the parent’s body weight. A normal human baby is only 5% of the parent’s body weight. That’s quite the big egg!

Not all eggs are used in breakfast. Dr. Jensen and his team use eggs for many other purposes, from stem cell research to hormone research. Frequently, they sex eggs taking a blood sample from the developing embryo to determine the gender of the chick. Because of Dr. Jensen’s research, they can do this with endangered species the Zoo and Safari Park. If a species has too many individuals of one sex, then the population can potentially become skewed. In an endangered species, this can become a big problem. Unlike humans, in birds the sex of the chick is determined by the female and can be influenced by many different factors. Dr. Jensen explained that the sex of a chick is almost always linked to the availability of food. Female chicks in some species are considerably bigger than males, so in a year where there is plenty of food a hen may lay more female eggs than males. In a managed care facility, like the Safari Park, food is always plentiful and environment conditions stable, which can also skew sex ratios.

Dr. Jensen let us experience part of the process of sexing an egg. In order to do this, we first have to be able to get inside it. Using a belt sander, we sanded off a part of the shell. There is a membrane underneath the shell, so nothing will leak out once the shell is gone. Under a microscope, we carefully removed the membrane so we could see the developing embryo inside. Though we didn’t take a blood sample from the egg, Dr. Jensen explained that he would then use a needle to take some of the blood from the embryo. Unlike humans, the blood cells in birds have nuclei containing their DNA. The DNA can be extracted and used to determine the sex of the chick. When the sexing process is done, the egg is sealed up with a special material and put back into the incubator to develop into a strong and healthy chick.

An egg is more than an egg! It provides a good source of protein that can be added to any meal. Can you believe it can also be used in many different types of research to discover ways we can help endangered bird populations? Whether on your plate or under a hen, eggs are nutritious and delicious, for you and the chick.

Libby, Real World Team
Week Four, Winter Session 2014