Thursday, May 9, 2013

Color blindness
Picture taken from here
I’m sure you have all seen pictures like the one to the left before, it’s one of the many pictures designed to be a test for color blindness. Color blindness is a relatively common problem and I’m sure we all have at least met someone that is color blind.  You have probably also heard that color blindness is a genetic disorder that effects mostly males because it is a sex linked trait. The normal X chromosome carries a protein that is used in color detection, without it the person is color blind. As long as the person has one chromosome that carries the protein the person isn’t considered color blind. However if you have read my previous posts I have told you that one of the X chromosomes in females inactive itself. This means that it’s not always as straight forward as you might initially think. A heterozygous (meaning that they have one effected chromosome and one normal one) female could be partly colorblind.
 


Sequential Hermaphrodites
 
This picture was taken from Here

Coral reefs are beautiful and exotic places full of all kinds of colorful and unique fish. Many of these fish may surprise you with something so foreign to us land walkers; they can change sex. These colorful fish like to maintain a certain ratio of male to female fish and if you remove one of their males a female will swiftly take his place. The opposite is true too of a male changing his sex and turning into a female and there are even fish that can be both sexes at the same time! I am not sure how these fish alter their sex since they must do it voluntary since there isn't something like temperature to force the fish to change its sex.
 
Sex determination in Reptiles

 
Figure 17.20. Temperature-dependent sex determination in three reptile species: the American alligator (Alligator mississippiensis), the red-eared slider turtle (Trachemys scripta elegans), and the alligator snapping turtle (Macroclemys temminckii).
This picture was taken from this site
Did you know, not all animal's sex is determined by sex chromosomes? Reptiles are a classic example of this. Some reptile’s sex is determined by temperature.  As you can see from the picture on the right, if a Alligators nest falls below 31 degrees Celsius all of her babies will be female but if she keeps her nest at about 32 degrees she will have all males. At about 31.8 degrees Celsius there is a mix of both male and females. This site explains this in more detail, but the general idea is that there is a enzyme named aromatase and this is used to turn testosterone (the male hormone) into estrogen (the female hormone). It is thought that 29 degrees to about 31 degrees Celsius aromatase is very active getting rid of all that pesky testosterone and making lots of estrogen and thus female babies. 
As cool as this system is not the way it works for all reptiles-- this doesn’t apply to snakes nor is it true for all turtles.

Sex determination in birds

Did you know that birds have a ZW system for determining sex instead of the XY system that we humans have? In birds ZZ is a male and WZ is a female. This makes the female the heterogametic sex instead of the male. When I read about this my first response was to ask does that mean that a bird can survive if it just has one Z? What would that bird be like? To my dismay however a bird cannot survive with just one Z and we don’t know what it would be like because it dies too early. This is because in birds one chromosomes doesn’t inactivate like what happens in humans instead both doses are needed.  My next question is can a ZZW bird exist then? The answer to this is yes but they are extremely rare and we don't have enough information on them yet to determine if it is the Z or the W chromosome that takes a more dominate role in deciding male and female. If you want more information This site talks about one of the three Charadrius alexandrines that have been recorded.
 On I related note I read Mile's blog and was very interested in Gynandromorphy so I looked up more information about it and found this article. They were experimenting on birds and one of the experiments that they did was they took cells from very early in development and moved them into a environment that was overwhelmingly of the opposite sex and tested to see if these cells would conform with their surroundings. They did not and it was concluded that the sex of the cell was determined at sperm entry.

Turner syndrome

In one of my old blogs I talked about Klinefelter syndrome which is when a male has two X chromosomes and one Y chromosome. I also said that in females, or males with Klinefelter syndrome, one of the X chromosomes inactivates itself (however it still plays a small roll and some proteins are still transcribed from it). So what happens if a female only gets one X chromosome since one inactivates anyway? The answer is that the female will have Turner syndrome. If you wish to know more information about Turner syndrome this site goes into much more detail. It says
Picture taken from
Here
"The most common feature of Turner syndrome is short stature, which becomes evident by about age 5....About 30 percent of females with Turner syndrome have extra folds of skin on the neck (webbed neck), a low hairline at the back of the neck, puffiness or swelling (lymphedema) of the hands and feet, skeletal abnormalities, or kidney problems. One third to one half of individuals with Turner syndrome are born with a heart defect, such as a narrowing of the large artery leaving the heart (coarctation of the aorta) or abnormalities of the valve that connects the aorta with the heart (the aortic valve). Complications associated with these heart defects can be life-threatening."
If after reading this you wondered what would happen to a male that had only one Y the answer is that they would not be able to survive since the X chromosome carries genes that are essential for human life.
 

 

For our last lab we were asked to take pictures of bubbles. The idea of this lab is to show that there is more then just the power of our DNA at work in our bodies. Our genes don’t tell our cells exactly how they should bend and their exact shape. There are physical forces that help with that. Bubbles are spheres because it take less energy to be a sphere then it does to be a square. When I look at them I can't help but think they do resemble the look of cells.  




          My initial plan was to take a time lapse of the fruit fly's courtship ritual. I came into the lab each morning at about nine for a week isolating the females from the males. I would recheck up on them between classes and make sure to remove any new flies from the vial that had the pupa in it into separate containers.  However when I put them back together they wouldn't mate. I think maybe I accidentally wrongly identified a male as a female and he contaminated my entire bottle of females. Anyway after that plan fell through I took this video of a larvae eating.
http://www.youtube.com/watch?v=5gT1VqD7PyM&list=HL1368130479
 Again I ran into problems with this video as you can see it it only one second long on youtube. I do no know how to fix this problem but the actual video is much longer. Thanks for watching :)

Wednesday, May 8, 2013

 
Klinefelter syndrome
A revisit to Tortoiseshell and Calico cats.
 
          I said in a previous post that almost all Tortoiseshell and Calico cats are female. This left the question of how can you get male Tortoiseshell or Calico cats? There is a genetic disorder named Klinefelter syndrome in which affected individuals have two X chromosomes and one Y chromosome. Just like in females one of the X chromosomes inactivates itself. If the male has two X chromosomes of different color then it will be a Calico cat. However having that extra X chromosome can lead to mild complications since it doesn’t fully inactivate. Humans can get Klinefelter syndrome too and mayo clinic has laid out the symptoms quite nicely according to age. If you would like to read it you can find it Here. Basically there is a chance you could get female qualities such as enlarged breast tissue and decreased testosterone. I said that there is a chance because not all males develop the same symptoms and on some occasions the syndrome goes unnoticed into adulthood.

 
 
 
 

 
 
 


For my lab I looked at the development of the heart in early chick embryos. The first image is a cross section of a chick at 33 hours. You can see the sonoatrial region of the heart beginning to develop.


The following three images are of a chick at 48 hours. The first two are cross sections and the third one is a sagittal section. You can see the dorsal aorta and the descending aorta.

 

The last image is of a embryo at 72 hours. it is a sagittal section. This image shows the descending aorta.

 
 




This week in lab we cultivated nematodes from earth worms that we let rot in a drawer for two weeks. The goal of this lab was to find and identify different stages of development. Unfortunately I was unable to find anything younger then a small adult.

However with that said I don’t believe my time spent in lab was wasted. I found out that these nematodes are actually pretty fragile. At first I was not adding water to my slide when I was viewing the worms and the most interesting thing occurred. The worm started to rip open before my eyes. It oozed its guts out and became a shriveled shell of the plump lively worm I was trying to view. Below are some pictures of the poor creatures.


I also saw several of what appeared to be worms inside of other worms. At first I thought it was two worms overlapping. However after watching for a while I saw the when the worm I presumed to be on top moved it brought its little worm with it, and the little worm could not squirm free of the larger worm.

The closest I could come to finding an egg or growing embryo was the following image however I believe that these could very well be a collection of bacteria and not at all what I was looking for.
The following is my personal favorite nematode. The first image is his entire cute little body followed by close ups of his insides and his anterior and postier ends.

 


 

Tortoiseshell and calico cats
Did you know that Tortoiseshell cats are almost always female? Have you ever wondered why that is? As I am sure you are aware, female cats, just like human females, have two X chromosomes. Males on the other hand only have one X and have one Y. The Y chromosome does not carry genes that code for color.
 A picture of a Tortoiseshell cat
taken from
Here
So since females have two X chromosomes does that mean that they are twice as dark colored as the males since they would have double the amount of color proteins? The answer to this question is no. This is because one of the X chromosomes inactivates itself. This is a random process that occurs early in development. If a cat has one X that carries a gene for black pigment and a different X chromosome that carries a gene for orange pigment then she expresses both colors in random blotches depending on which X chromosome remains active. Once a cell inactivates one of the X chromosomes all the cells that are descendants from that cell will all have that same chromosome inactivated. This is why there are blotches of color rather than the cat looking more like a checker board with lots of tiny dots of color. The earlier in development the cell inactivates one of its X chromosomes then the bigger the blotches will be. Also since inactivation of a X chromosome is a random event, even if two cats shared the exact same genetics they would not have the exact same color pattern.
Picture of a Calico cat taken from
Here

Calico cats work the same way as Tortoiseshell cats, except calico cats express a different gene that is independent of the X chromosomes that codes for a white color.