Life Sciences lab classes explained

On Tuesday you will be separating out your PCR products according to size by using agarose gel electrophoresis. This technique relies on the fact that DNA has a   net negative   charge (think of all those phosphates along the phosphodiester backbone). So if you put DNA in an electric field it will move towards the   positive electrode .... in practice we put the DNA into a jelly-like material called agarose, and the DNA moves through this agarose when an electric current is passed through it. The cool thing is that large DNA fragments will have a hard time getting through the gel, so they will travel slowly. Small DNA fragments, on the other hand, have much less trouble getting through the gel so they move faster. This means that we can use this technique to separate DNA fragments based on their size....... Here is what happens with agarose gel electrophoresis with a step-by-step description underneath: image taken from: http://www.all-science-fair-projects.com/science_f

So once you have isolated genomic DNA from some peas, you need a way to assess how much DNA you have got, and how pure you have managed to get it.... This can be done using a   spectrophotometer  taking advantage of the different absorbance spectrums of DNA and the common contaminants, RNA and proteins. As I have shown in the diagram of an absorbance spectrum below,  DNA  absorbs light most at a wavelength of  260nm ,  protein  absorbs light most at   280nm .  A   DNA/Protein mixture  on the other hand will have a spectrum  somewhere in-between  -  exactly where this spectrum will be depend on how much DNA vs protein there is in the sample. So when we are assessing how much DNA we have, the absorbance of the sample at 260nm can be used to estimate this.  And when we are assessing the purity of the sample (i.e. how much protein contamination we have), we can find the ratio of the absorbance of the sample at 260nm : the absorbance at 280nm  (in other words you divide the a

In practical 9 you will be isolating the DNA from peas - this might seem like a long drawn out process, and you might not really know what you are doing.... so here are the steps explained :) I hope that helps you understand what you are doing in the lab! 

You are also going to need to know about Mendel's second law....so here is a heads up: Mendel's Second Law: The Law of Independent Assortment This law is about the inheritance of more than one trait i.e. more than one set of gene pairs/alleles... During gamete formation,  alleles for one trait will separate into the gametes  independently of alleles for another trait. In other words, the way one pair of genes segregates into the gametes is not affected by the way a different pair of genes segregates into the gametes. This means that the inheritance of one trait is not dependent on the inheritance of another. Take a look at this Punnett Square: image taken from: http://course1.winona.edu/sberg/241f07/Lec-note/Mendel.htm The Punnett Square above shows the possible genotype and phenotype of pea plants with respect to their pea colour and pod colour. Here is a description of what this Punnett Square shows: The

You won't get too far in your fly experiment if you don't know about  Mendel's laws . These laws describe the  fundamental principles of inheritance . Amazingly, Mendel figured this all out by studying pea plants (over 10,000 for 10 years) way before DNA and Genes were understood.  Mendel first reported these laws in 1865 but they faded into obscurity until they were rediscovered in 1900. A couple of definitions: GENOTYPE  =  What genes a cell contains PHENOTYPE  = T he characteristics/traits of an organism  Anyway, that is enough preamble --> to the laws.... Mendel's First Law: The Law of Segregation   Every individual has a pair of genes (alleles)  for any particular trait.  Each parent passes on only one allele to each of their gametes - by meiosis.  Gametes randomly come together,  hence offspring will have again two alleles for a particular trait,  one from their mother and one from their father. The dominant allele will dete

In practical 1 this semester you will be setting up crosses with   Drosophila melanogaster , aka the annoying fruit fly! So it is going to be pretty important for you to be able to tell the boys from the girls... Here are some pictures to help you out: This first pic is a diagram comparing the male and female fruit fly - the main things to note are The female is bigger than the male The male has a rounded abdomen The female has a more pointed and elongated abdomen  The dark banding on male abdomen increases towards the back, with the end of the abdomen being totally black The female abdomen has much more uniform stripes  image taken from: http://en.wikipedia.org/wiki/Sex-determination_system And this second pic is a real life picture of a female (on the left) and male (on the right). image taken from: http://www.berkeley.edu/news/media/releases/2002/07/03_paras.html One last thing, if you look reeeally closely, you can see that the males ha

Sometimes when you are dealing with an exponential graph it is just a whole lot easier to convert the exponential graph to a straight line graph (you have done this a couple of times already in 107). For example, remember this graph - it shows how growth rate increases with increasing temperature, and the part of the graph between points a and b represents exponential increase in growth rate with increasing temperature. Now remember this equation: Where  Rt2  is the  rate of growth at temperature 2 Rt1  is the  rate at growth at temperature 1 Q10  is the  factor by which the rate increases for every 10 degrees increase in temperature t2  is  temperature 2 t1  is  temperature 1 (and remember the dot is a short hand way of writing a times sign -'x') If you want to calculate Q10, how are you going to do it? You could read a couple of points off the exponential graph and enter them into the equation above, and then re-arrange it to solve it