Introduction to Genetics

Faith sent me an email expressing an interest in better understanding DNA, genes and chromosomes. She proposed a thread with goals the same as Introduction To Geology, but for genetics instead of geology, and she included a list of questions, which I include below. Faith will be participating so that this can be interactive.

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If you have some cells of some creature but don't know what creature it is, is it always easy to identify it from its DNA?What are the defining factors: the number of chromosomes only?If you have DNA from strikingly different breeds of, say, dogs, say a greyhound, a chihuahua, a black lab, a Bichon Frise, a Dalmation, or take your pick of what are the least similar -- are you able to tell which is which from just looking at the DNA and what exactly do you look for?Apparently it's possible to determine close relatedness of family members from their DNA. What exactly are the most important clues?Do you ever actually look at the DNA itself or are you looking at some sort of indicator, model, or whatever you call it that you somehow derive from the cell? I know a DNA portrait as it were is often represented by some sort of bars that to me are indecipherable. Do I have to learn what those mean in order to get answers to the sort of questions I'm asking?Apparently the DNA in different body cells is different. Can you nevertheless identify the creature from any of these different cells? Or, what SORT of difference are we talking about?Apparently a gene is a segment of the DNA strand and it can be a very long segment, even of thousands of paired chemicals, and there is some kind of chemical sequence that is different from the body of the gene that tells you where it begins and ends. Or something like that?The function of some genes is known, and can even be predicted across different species. That is, you know where the gene for oh say eye color is located, or the many genes that determine eye color if there is more than one, and this is predictable for many species. Or is it?Generally speaking, are there many traits that are governed by more than one gene?Where is the "junk DNA" located on the DNA strand? Is it interspersed with functioning genes or collected all in one place or what? Is there some way you can tell by just looking at it that it's "junk" or how do you tell?Homozygosity is the pairing of identical forms of the gene, is that right? Does that mean an absolutely identical chemical sequence on both sides of the pair?Whereas heterozogosity is the pairing of different alleles or different forms of the same gene, meaning a different chemical sequence on both sides of the pair? Or something like that?