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Hi Dr. Pat,
1-How much DNA is unique to an individual?  2-What steps are taken to make sure a DNA sample that is collected from a crime scene is not contaminated?  3-What is used to cut DNA into small segments in order for it to be analyzed?  4-Explain how DNA can be used to solve problems that do not involve crimes.
Thank you,  Sue

Hello Sue
Well these sound like forensics questions and I will not be able to answer all of them. 

What I can say is, unless you are a twin (or triplet...) your DNA taken all together, is unique to you.  I presume, though, you want to know how much of the sequence is not ever found in another individual.  I'd be likely to say, almost all of it is shared by another individual, somewhere on the planet.  That is why the forensics is geared toward the number of repeated units at various locations on different chromosomes - so that a set of data can be compared person to person.  The set is more likely to be unique than any one location.

I do not know how crime scene samples are handled to ensure they are not contaminated.  Good question, though.

Restriction enzymes are used to cut the DNA in a reproducible location.  These enzymes are found in a variety of bacteria and purified for this type of laboratory use.

Besides crime investigation applications, DNA is useful in determining who is related to whom.  This can be as current as who is the father of this particular child.  Or, it can be archeological/historical in nature as answering the question, is Butch Cassidy buried in this grave?  In addition there are vast applications using DNA sequence analysis to determine how evolutionarily distant or near two species are and when they diverged.  The huge Human Genome project sequenced all of the DNA of a human and differences will now try to be determined to identify genes related to a variety of cancers.  Great medical implications fall out of this one.

There is so much more we can learn from the sequence of DNA.  But, mostly we learn how very much alike we all really are.

Thanks for your questions.
Dr. Pat

First and formal , my name is Eric and I am from Singapore.  I am currently in a discussion about cloning.  I have read your website and have found lots of things that I require... thanks so much for your website, it is an excellent one.

I just want to ask your opinion on whether cloning should be banned? and if cloning is successful, what are the positive and negative effects of it?  Thanks so much and hope to hear a reply from you soon.

Hi Eric,
Thanks for your question. It is a very deep question, indeed, and I can only scratch the surface of it.

First let me say that science and society have influence over one another, much more than is generally acknowledged. And, sometimes it is important for society to ask these ethics-oriented questions of the technologies that science is producing. Scientists are members of society, obviously, and they need to be in this conversation, too.

Let me backtrack to two examples of society's ethics debates. One is way back when medical doctors wanted to learn about anatomy by dissecting the bodies of dead people. Much of society was aghast at this practice, but doctors answered back that the benefits to medical science were invaluable. Another was not that long ago when the first 'test tube baby' was born. You don't hear that expression anymore, but a couple of decades ago society wondered if it was a good or bad thing and there was much discussion of the balance between helping couples who could not have children, versus the inclusion of a petri dish into the normal process of conception. So, this is just to tell you that discussion is valuable - perhaps indispensable.

The issue of cloning is one of degrees and the real question is: where does it change from a probably ethical use of technology into an unethical or abhorrent practice? For instance, I would not at all be against cloning cows to produce milk that contained important pharmaceutical drugs that could be used to treat human illness. But, if somebody wanted to clone a human because they wanted to create a 'master race' or, indeed, a 'slave race' I would be adamantly opposed. Personally, my way of looking at the aspects of human cloning revolve a great deal around wondering what the motives of the scientist are. I think the beauty of the human race is as much in our differences as in our similarities. Until someone can show me good reasons for cloning humans, I'll have to stay in the 'opposed' column.

But, bringing this back to the beginning of my response - this decision must be made by all of us together. It is through discussion of the thorny issues of ethics and motivation and benefits that we will chart our best course.

Meanwhile, we also need a conversation about - what happens when a person is cloned despite whether society thinks it is good or evil?
Dr. Pat

Hello, I am a student I want to know the answer for this question :  what are the forces that stablizes the DNA? thanking you   Natilie

Hi Nithya,
Well, I assume you mean the forces that keep the DNA in a nice double-helix form. That would be the interaction between the bases on each strand and the interaction of the stacks of paired bases along the length of the DNA.

The first - interaction between the bases on each strand - is simply the matching of A with T and C with G. There are two non-covalent bonds that form between A and T and three between C and G. Non-covalent bonds are the attraction of a positive with a negative charge. This is a fairly mild bond compared to a covalent bond. In our ICanDoThat pages we compare non-covalent bonds to sticky glue and covalent bonds to super glue. The individual bases are charged. This attraction between the bases on one strand and the bases on the other strand of DNA add up to quite a strong attraction. Much like a small strip of Velcro is easier to pull apart than a long strip.

The second - the interaction of the stacks of paired bases - has to do with water-loving versus water-hating compounds. Charged compounds love water, uncharged hate it. Meaning that uncharged compounds will glomp together to stay as far away from water as possible. Add a little cooking oil to a glass of water. Oil is water-hating and it does not dissolve in the water, but, rather is repelled by water. Stir a little and you will see the oil return to its own layer. Using a clean water sample, add table salt to the water. Stir a bit, and you will see it will dissolve since salt is charged and loves water.

Well, once the bases on each DNA strand non-covalently bond to their pairs on the other DNA strand, they neutralize the charges of the bases. While individual bases are charged, base pairs are not charged. Since they are not charged, they hate water. So, all of the base pairs cling together as far away from the water as they can get. The phosphate backbone of the DNA is charged and loves water. Between the two you get the famous double helix form.

Let me know if I should try to explain this a different way. Good luck !
Dr. Pat

I cannot find this answer anywhere.  What organelle does the cleaner (disinfectant) target to kill the bacteria.  I have looked for hours and your help would be appreciated.  Thank you, Brian.

Hi Brian,
Well, you have asked quite a complex question.

If you are talking about chlorine-based disinfectants, the question has been asked by scientists regarding how white blood cells (neutrophils) kill bacteria. There is an enzyme in these cells, myeloperoxidase, that produces the active ingredient in Clorox. Bacteria are pulled into the cell and surrounded by plasma membrane to create what is called the 'phagosome'. Inside the phagosome, myeloperoxidase (which is an intense green color, by the way), produces HOCl or hypochlorous acid. This is the active ingredient in Clorox. The concentration of HOCl inside the phagosome rises to that of full strength Clorox. HOCl reacts with many things, including amino-containing compounds. That would be proteins and DNA, primarily.

Unfortunately for the bacteria, and unfortunately for your question, this is rather indiscriminant regarding specific organelles. If you have to pick one, perhaps it is the plasma membrane which gets holes in it and therefore the cell is, in effect, burst. But, then, others would argue that the killing action occurred because enzymes in the cytoplasm were de-activated and the cell could not carry on its necessary functions.

But, backing up a bit, an antiseptic is an agent that can kill bacteria, but is mild enough to be applied to the skin. Soap would be an example of an antiseptic. A disinfectant, though, is too strong to apply to the skin and is used on surfaces only, such as bathtubs, sinks, tabletops. Comet or Ajax powders used for cleaning bathtubs and sinks would be examples of a disinfectant.

I found the search term "bactericidal action disinfectant" to produce results. But, all of the articles suggested that the various disinfectants acted by different means and all were generally taken to act in a non-targeted manner.

The following article was quite readable and thorough regarding a variety of disinfectants and their modes of killing bacteria.


And, too, I found a science article from the Journal of Antimicrobial Chemotherapy suggesting that the method of action of disinfectants should be studied as they may have beneficial effects when used in combination with antibiotics, such as penicillin (which are taken internally to to fight infections).


So, long story short, you have asked a very broad question which has received, and continues to receive, the attention of scientists.

I hope this helps.
Dr. Pat

Thank you for responding so quickly.  Thanks again.  Sincerely, Brian.  P.S.  Now I know a great place to look for information, your web site is great!

What is the difference between plant cells and animal cells.
Thanks, Jim

Hello Jim,
The difference in structure would be that plant cells have a cell wall and may contain the chloroplasts and vacuoles, while animal cells do not.
Hope that helps,
Dr. Pat

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