biol+4+faq+(nsfaq)+aos1

If you have any questions or are uncertain about anything to do with the course, then this is the place to get help. I will try and respond to your query as soon as possible, although I strongly encourage you all to try and answer the questions first.

For a question type in **#750a56** to change to **dark magenta** For an answer type in **#17066a** to change to dark purple Or choose any colour combination you wish. Please use this page for area of study one queries. A link for area of study two is below. biol 4 faq (nsfaq) aos2


 * Q. Ok I'm not really sure what it means when it says the chromosomes "thicken" or "condense". I assumed that it meant they double, but then it says they double just before mitosis (in interphase). I was just a bit confused as to what the whole 'condensing' thing meant and what the purpose of it was. Does it maybe refer to how they get this distinct and visible shape? **

//A. This is an important point that you raise. You are absolutely right in thinking that DNA replication occurs prior to mitosis/meiosis. Hence the "thicken and condense" does not refer to chromosomes replicating. It refers to the chromosomes themselves in the way they are packaged. As each chromosome (really a pair of sister chromatids) condenses, in other words becomes more tightly packaged it shortens (think of a piece of string that is linear and then scrunched up). Because all chromosomes are doing this they start to become more separated from each other and thus visible as separate entities under the microscope.So your last sentence is spot on! VM//

IGNORE THIS QUESTION! it has to be germ cells that replicate not gametes, sorry hehe **
 * Q. hi Voj, in meiosis can gamates replicate into four diff gametes or do they need a germ cell to make a four diff gametes. I dont know if i'v said this normally hehe :)

//A. It is important that you are clear on this point, and it now seems you are. Good you are absolutetly right. Don't ever think that gametes undergo meisois because they don't! VM//




 * Q is a probe the same thing as a primer. Not so sure what probes do besides find the gene wanted and show where a particular gene is via radioactive coulor thanx :) **

//A. Good question. Terminology is always confusing. Both a probe and a primer are essentiall ythe same thing and work in the same way. They are short pieces of single-stranded DNA that can attach to complimentary sections of DNA or RNA. However, their purpose is different. They are called primers if they are used to allow for synthesis of more DNA, ie for polymerase to have a starting point,for example in PCR and in natural DNA replication. Probes are not used for this but for (as you said) being able to detect the presence of a certain nucleotide sequence, hence show up a certain gene or maybe a mutation. VM //


 * Q. when using the gel electrophoresis to test if a person is a carrier for CF, it says you need a normal perons gene sample, the patients sample and a standard sample. Is the standard so you know that each line is made up of a certain amount of bases letters, so you can compare the other 2 samples 2 that one :) **

//A. yeah, the standards are a way of verifying what length of fragment the bands represent. This is useful in checking that the experiment has proceeded correctly, in that the DNA has been cut up correctly. VM //



Edit: Oh and another thing, when we count the base-pairs of a DNA fragment, do we include the sticky-ends? **
 * <span style="COLOR: rgb(117,10,86)">Q. Hi Vojtech, the table 9.2 on the RFLPs sheet is quite confusing. I know that RFLPs are variations in DNA sequences that can be cut by restriction enzymes...so when it asks the Number of RFLPs do we just need to say the number of times the enzyme (TaqI or EcoRI) would cut that DNA sample? Also when it asks for base pair lengths, does it mean the number of base pairs on the recognition sequence?...or something else maybe [CONFUSED]. I'm just not sure what it is they actually want me to write..

//<span style="COLOR: rgb(19,22,241)">A. Ok, if you have a single piece of DNA, which is then cut once by a restriction enzyme, how many RFLP fragments will there be? TWO! So, in linear DNA number of recognition sites(cuts) is always one less than the number of pieces produced. eg 3 cuts = 4 fragments. However, if the DNA is circular (as in a plasmid) and there is one cut made, you still end up with one piece of DNA (but linear). Two cuts will result in 2 pieces of DNA. VM //

//<span style="COLOR: rgb(19,22,241)">A. The base pairs will refer to the length of the DNA fragment produced as a result of the cutting. How many letters make up one strand of the DNA fragment, do not count both sides. This should take care of your last query. Yes, include the sticky end bits but be consistent in which strand you are using to count the length of each DNA fragment. VM //


 * <span style="COLOR: rgb(117,10,86)">Q. Just wondering exactly how much we have to know about mutations? Because the textbook only mentions Point Mutations. But would you say we still need to know about block and chromosomal? **

//<span style="COLOR: rgb(19,22,241)">A. you definitely need to know about point mutations and chromosomal abberations (whihc is discussed later in the textbook), block mutations is just an extension of point mutations and I think you are a better off being familiar with them. VM //


 * <span style="COLOR: rgb(117,10,86)">Q. Vojtech in the course notes you mention that when a base substitution results in a STOP codon being formed, it is called a nonsense mutation. If a STOP codon is formed as a result of an insertion or deletion, could you still call that a nonsense mutation? Just a bit unsure about that one. **

//<span style="COLOR: rgb(19,22,241)">A. Hmm... i suppose you could call it that, although I cannot be 100% sure. the thing with insertion and deletions is that they alter all the codons after the mutation so we are talking about a major change in the polypeptide formed anyway, whereas in the substitution it is only that one codon that will be affected. i would be surprised if you were asked to recall or use these terms, like nonsense, it is more important to understand the effects. Certainly be familiar with the term "frameshift". VM //

Q. Hi VM. Can you please put all the course notes up on the wiki? Thaaaaankkkksssssssss.

//<span style="COLOR: rgb(19,22,241)">A. I have put all the course notes given so far on the intranet. if you have any issues accessing it, let me know. You need to go to "curriculum" and then 12biol class. VM // Yup got it. thanks for that :)

Q) In how much deatil do we have to know about the southern blotting technique??

//<span style="COLOR: rgb(19,22,241)">A. First of all EJ, I have left a message on your mobile, I am unable to respond to you message via wiki email from school (which is where I am), so check it. I have answered this question in the SAC section, if you are refering to how much you need to know for the SAC. Seeing as I haven't covered this in class, you needn't worry about. VM //


 * <span style="COLOR: rgb(101,10,86)">Q. Just wondering, let's say we get a question where we're told (for example) that two mice were crossed several times and they produced 15 black offspring and 5 white offpsring. If we're asked to prove which characteristic is dominant, how exactly would go about doing so? Should we mention the 3:1 ratio, and that both parents are heterozygous? I'm just sort of confused as to what I should specifically mention in order to do this. **

// A. Does it say what colour the intial mice were? I would need to see the question to be more sure of what sort of answer is expected. If you are told that mice could be black or white and that it is to do with one gene with two alleles, then you can use the 3:1 ratio as an expected ratio for a cross between two heterozygous individuals. This would also mean the two parents were black. There is no way you could get the results if the two parents were white or even if one was black and one was white. VM //


 * Well it doesn't say what colour the initial mice were. Just that possible phenotypes are Black or White. So to state the dominant phenotype can we say something "a 3 (black) to 1 (ratio) indicates both parents were heterozygous and had the black phenotype, meaning the black phenotype is dominant". Can I say that? **

// A. Yeah, i think that you are ok in your conclusion based on the info given. VM //


 * Q im sort of confused about mono and dihybrid crosses. Whats the difference, i know that monohybrids are one characteriistic controled by one gene on a homolohgous pair and a dihybrid are two genes controled by two homologous pairs. Isnt dihybrid the same as monohybrid but with two genes?? **

// A. Your last comment is pretty much it. Dihybrid involves looking at two genes each with two different alleles, unlike monohybrid which involves only one gene. But you have to be careful about saying dihybrid is to do with two homologous pairs because if the two genes are linked then it will involve only one homologous pair. STRICTLY SPEAKING though, dihybrid crosses are where you have two F1 individuals (heterozygous) and are looking at two traits. Eg AaBb x AaBb. A monohybrid cross would be Aa x Aa. It is better to look at this section in this way. There is single gene inheritance and two gene inheritance. It is very unlikely that you will have to define the terms monohybrid and dihybrid anyway. What is important is that you understand what happens when two genes (traits) are being looked at or if there is only just one. VM //

Hello vm. I hope your having a nice holiday away from your favourite class and arent missing us too much. 1. In 'dihybrid cross' worksheet, they used the words 'oocyte' and 'spermatocyte'. Havent come across this before, and wasnt sure what it is and if we need to know it.

// A. These are terms that would be worthwhile to be fmailiar with. Although, I don't think not knowing them should have prevented you from answering the questions. A tip for you. A word ending in "cyte" refers to a cell. Spermatocytes are cells that undergo meiosis to eventually produce sperm. Similarly, oocytes undergo meiosis to eventually produce egg cells. I said to you that germ cells undergo meiosis to prodcue gametes. These are the two names given to these germ cells. VM //

2. In the 'inheritance patterns' sheet question 5b asks why more females than males would be affected by sex linked dominant trait (on x chromosome). Is it okay to say, because females have 2 X chromosomes nad males only have 1, thus females have double the chance of inheriting the infected gene?

// A. Yeah that's on the right track but I would also include the fact that females can therefore get an affected X-chromsome from either parent whereas males can only get it from one of their parents (mother) as father will always pass on a Y chromosome to a son. VM //

3. 'crossing over problems' question 4. Explain the genetic significance of crossing over. I really didnt know how to answer this?

// A. Crossing over increases the genetic variation in the offspring because without it linked genes would always be inherited together. So crossing over in effect means that even though many genes occur on a particular chromsome, gametes can have a variety of combinations as if the genes were on separate chromosomes. Genetic variation is important when we look at the cocnepts of natural selection and evolution in area of study two. VM //

4. if we're asked for the phenotype, can we just say for example 'black' or do we need to say 'homozgous black' or 'heterozygous black'?

// A. Hmmm... this really depends on what infromation you are given and the wording of the question. Phenotype is the observable characteristic due to the combination of genes/alleles. So black should be a good enough answer. VM //

5. Im a bit confused with the worksheet "patterns of inheritance", Q2,3,4,5!! Can we please go over it in class.

// A. Are you refering to the "test your understanding" sheet? If so I will put answers up in the "solutions" section hopefully later on sunday. Otherwise we can go over stuff in period zero on tuesday. VM // // PS these are important questions that you have raised, so well done! VM. //Thanksssss vm. see you on tuesday.

Q. when a queston asks 'explain why more females than males will be affected' when dealing with sex linked dominant traits, whats the answer?

// A. I suggest you look at the answer given above to Q2. I think it may be the same question that you are asking. :-) VM //