Introduction to Genetics

Thanks, TAQ, for your thoughtful replies.(Took me so long to answer because I didn't see the "request password" link when I tried to log in)I wrote out one long reply to both your posts and was driven to the conclusion that there’s just too much here to try to respond to all of it at once and maintain any kind of order, so I decided to try to limit things by focusing on one question at a time. So you are apparently giving a yes to this question because now it is possible, by the various means you mention (that are technically rather over my head), to find out at leastwhat kind of critter you are working with. I gather it’s not easy at all since it does require quite a bit of technical work to arrive at the conclusion but that you CAN indeed find out the species.So I'd sum up:ANSWER: YES, WE CAN IDENTIFY THE SPECIES, BUT IT’S NOT EXACTLY EASY.Fair enough?I am a bit surprised because I did assume that the number of chromosomes would be the major indicator, which I also assumed wouldn’t be hard to determine, but you didn’t address that part of the question. (What are the defining factors: the number of chromosomes only? )If my paraphrase of your answer is correct enough I’m happy with it, but I don’t want to move on until any further thoughts on the subject that might occur to anyone are considered.P.S. I did look up some unfamiliar terminology but think I'll leave the technical parts of the answers to later. Right now they could get to be a long rabbit trail.

Dr. A: Thanks and I may need your help with getting some answers in more accessible English at least, so I may well ask some questions of you.I’m glad to hear you’ve been thinking of doing a course on genetics for beginners as I very much appreciate your course on geology.What I told Percy is that I would like to see such a course done but expected it would rapidly get over my head, so I didn’t really think of this thread along those lines, but as a way of learning more about some particular questions I’ve had in mind for some time.

Thanks for all the answers about chromosome number.I'm going to get lost if we don't stick more or less to the order of the questions. Although that's an artificial order it IS an order.It looks like Question One is finished so on to Question Two. ANSWER: NO.OK? From the article on DNA profiling: My thoughts on this would probably lead down too many rabbit trails but I’ll mention this much anyway: I think I knew that a great percentage of DNA merely identifies us as human so that what identifies us as individuals involves a very small percentage but it helps to have it repeated. I would suppose then that a breed or a race of a Species might eventually be identifiable by certain characteristics within the smaller percentage and that this may be established some time in the future. Or make that a question.Again, I’ll wait for thoughts about this one before going on to No. 3.

Hi Crash.
This answer from you is going to be useful when that question comes up but please let's wait. I should have realized all those questions could drown a thread, but some of them will probably be answered fairly quickly.

Hello Percy. I think I'm getting it about chromosomes, that numbers are shared between different species so can't be used to identify a species without further investigation. Apparently I had a very oversimplified notion about that.You are saying that all individuals of a species have the same number of chromosomes, but didn't someone here say that even within a species some individuals may have a different number? Ignore this if I got that wrong. I didn't review the whole thread. PaulK's link gives the biggest number to a fern called "adders tongue" at a staggering 1440 chromosomes.Now I'm getting more curious about chromosomes. What on earth IS a chromosome anyway? It SEEMS like it's just arbitrary segments of DNA that COULD have been simply one long string instead. Is there any point to its being broken up into separate chromosomes? Do the different chromosomes have some identifiers that give them particular functions? Not sure what I'm asking, it's hard to get the questions clear.it's very interesting that a particular gene is always located on a particular chromosome. Is this true across species in some overall general way, that genes for particular traits that are shared among different species show up on the same chromosome sort of more or less? Meaning for instance eye color which is always the one that comes to mind for some reason, is that gene or set of genes always located on a chromosome that is the same in all species where variations in eye color are a factor?Are my questions making any sense?

Hi NWR,
Yes, I think it's becoming clear that breeds COULD be identifed by DNA but that it would take the building up of a library or database of the identifying sequences for each. It's more a technical problem than a conceptual probleml, as you say.

Maybe you answered it and I didn't recognize it, but the question I had in mind was whether the chromosomes might be identified by the particular genes that reside there? They are numbered so that you run across such statements as "such and such a gene on Chromosome 15," so the question is whether this sort of locatability perhaps gives a chromosome its peculiar identity, even a raison d'etre.

Yes, I think that is the question I'm trying to ask. Maybe someone else will have the answer.

This is the sort of frustrating information I've thought might be the case. So you are saying that genes on say Chromosome 12 can trade places with genes on Chromosome 8, I assume during meiosis -- I also assume it would be a comparable chunk size-wise? -- so that pretty much does in any idea that the chromosome can be definitively identified by its set of genes. Or is there nevertheless some rule to this sort of event, rather than the randomness it sounds like?But let me ask: Is this swapping a rare occurrence or fairly common?{ABE} Also, I'm assuming the DNA strand doesn't break for this exchange to take place, break apart and come together again, so it isn't exactly right to say that a whole GENE is being moved, is it? Is it right to say that whatever alleles are getting paired for particular genes are getting placed on the opposite chromosome or something like that?Edited by Faith, : No reason given.

Hello Adversary Anglagard. Perhaps you'll be able to find time for a zinger or two between your courses.Thanks for the recommendation but I've got such a long list of books I'd like to read and never will, that one doesn''t stand a chance. The point of this thread is to raise some particular questions I've had about DNA for some time now, about DNA in general and not particularly about human DNA if at all.I think the thread really should be titled something like "Questions About DNA" rather than "Introduction to Genetics" which would better describe what Dr. A has in mind for a future project.

Aha, "numbered in order of length." Thanks, Crash, a nice simple direct practical answer.I actually have some questions about this occasional occurrence of a different number of chromosomes in some individuals, but the questions are pretty blurry at the moment, will probably get back to them later.Edited by Faith, : No reason given.

Thanks for everybody's input on chromosomes. I'll never get all of this straight I'm sure but some of it is sinking in.I did go look up meiosis and mitosis and watched some animations, more than once. Thought I knew about cell division all the way back in high school already, but I'm finding that it's hard to retain the details in mind after watching even many times. Just getting old I guess.But watching them did make me aware that chromosomes aren't just arbitrary bits of DNA, they have a structure, even down to the "centromere" and the cell division process acts upon them rather strikingly.Could get bogged in detail if I pursue any of this further so I'm going to go on to another question.

OK, we can think about the question you answered, Crash. I'm skipping over #3 for now just because it doesn't interest me at the moment. [qs] You post a picture of a test tube with some white filaments at the top. That's the DNA out of the peas? But what IS direct sequencing? You look at the DNA strand under a microscope and count off the chemicals?Taq seems to be saying something somewhat different: I doubt I'm going to get very far into learning much about the secondary techniques involved in reading DNA. My questions come more from wanting to be able to visualize the DNA strand and what's going on there more than anything else. There are plenty of Wikipedia articles that do give diagrams that demonstrate various DNA events, such as different kinds of mutations.Maybe I don't know what I'm asking.But again: In direct sequencing are you actually looking at an actual DNA strand and what does it look like? I'm sure the diagrams are accurate enough but the reality must be a lot messier.

That's all really helpful, sorts a bunch of stuff out for me. Thanks. Now I can see I'm going to have some questions about the actual sequences, the CAGT sequences and what they tell you.For starters let me guess, you don't sequence an entire gene, which is too huge, but there are parts of the sequence that give you useful information about it?

Hello Crash,
Sorry I've been so neglectful of this thread. Hope I can get back to it with more concentration soon.Didn't want to let things get out of order here but maybe it's OK as long as the subtitles identify the topic. I really would like to know about "Junk DNA" and was going to skip to that question anyway when I saw Dr. A's post with the diagram of the Human Genome here: EvC Forum: Flood Geology: A Thread For PortilloIt doesn't even mention Junk DNA. Can you explain?ThanksABE: The Wikipedia article on Noncoding DNA seems to suggest that the term Junk DNA applies to all DNA that does not produce protein.Non-coding DNA - WikipediaReading through this site I see a description of Pseudogenes that fits my understanding of Junk DNA: I don't see an indication of what percentage of the Genome is pseudogenes.Then there is a discussion of Junk DNA farther down which also fits my understanding, that is, formerly functioning DNA that was killed by deleterious mutations: Obviously I could think a lot more carefully about all of this than I have and hope I can eventually. Meanwhile it looks like a starting point.P.S. I'm counting on you to be able to reduce this to a practical, manageable, digestible summary for the nonscientist. Edited by Faith, : No reason given.Edited by Faith, : No reason given.Edited by Faith, : Add P.S.