1) Autosome = a chromosome that is not a sex chromosome. For example, in humans there are 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females or XY in males).
NUMBER OF CHROMOSOMES
2) Aneuploidy = a chromosome abnormality where there is an abnormal number (extra or missing chromosome(s) / +1, +2...etc or -1,-2...etc chromosomes) of chromosomes, due to nondisjunction in mitosis/meiosis I/meiosis II. Eg. Monosomy = presence of only one chromosome (instead of the typical two in humans) from a homologous pair.
3) Polysomy = when a diploid organism has at least one or more chromosome(s) than the normal (diploid) number, due to nondisjunction. Eg. Trisomy = 3 copies instead of 2 copies of a particular chromosome (eg. Trisomy 21 in down syndrome).
NUMBER OF SETS OF CHROMOSOMES
4) Polyploid = cells with more than two paired homologous sets of chromosomes (diploid, 2n). For example, triploid (3n/ cells with 3 times the haploid number of chromosomes/ 3 sets of chromosomes) and tetraploid (4n/ cells with 4 times the haploid number of chromosomes/ 4 sets of chromosomes).
Hope that this is less confusing for you guys now. Since I've already covered most of the terminologies of your SDL on nondisjunction here, i expect all of you to be able to answer most of my questions next week during the tutorial! ;)
Hi miss teong
ReplyDeleteI have questions from the TYS.
1.If asked to outline structural differences between amino acids & nucleotides, is it acceptable to say that one has an amino group, a carboxylic acid group, a hydrogen group and an R group but the other has a pentose sugar, a nitrogenous base & a phosphate group? What other points should I include in my answer?
2.“Describe, with examples, the roles of proteins in membranes (6marks)”. I have identified: 1. serve as receptor proteins 2. allow enzyme-catalysed reactions to take place efficiently 3. connect adjacent cells in various kinds of junctions 4. cell-to-cell recognition 5. attachment to cytoskeleton & extracellular matrix. What other points should I include in my answer?
3.“Explain the need for reduction division in meiosis (6marks)”. Is it sufficient to mention the importance of maintaining stability and ensuring genetic variation?
4.“Explain how ribosomes differ from lysosomes (8marks)”. I’ve only identified the fact that lysosome has single membrane and ribosome has no membranes. What other points should I include in my answer?
5.“Cells have metabolic pathways commonly made up of sequences of enzyme catalysed reactions. Explain, with examples, the advantages of such sequences of enzyme catalysed reactions (6 marks)” I’ve no idea how to answer this question..
Pls explain these qns, thanks!
Hsin Fen
Hi Hsin Fen,
Delete1. How many marks is this question? Yes I think you can compare their respective structures as you have stated above. You can improve your answer by further elaborating: For amino acids, they have the groups mentioned above attached to a central carbon atom. You can also say that that the R groups have different properties (charged/polar/nonpolar etc). As for nucleotides, you can say that the pentose sugar can be a ribose (in RNA) or a deoxyribose (in DNA) and the nitrogenous base can be either adenine/guanine/cytosine/thymine/uracil.
2. Since the Q is worth 6 marks, i think you can pick three functions (out of the 5 that you have mentioned) to talk about, with further elaboration using EXAMPLES as required by the question. Actually, some of the examples will be learnt in the later topics on respiration/photosynthesis/cell signaling so you may not know the full picture for now. But ill give you some examples.
I think the easiest points to elaborate on is that proteins serve as (i) receptors (eg. receptor tyrosine kinase; you will learn it later), (ii) transport (eg. aquaporin water channel), and (iii) enzymes (eg. adenylate cyclase that converts ATP to cAMP).
3. Meiosis does NOT lead to genetic stability. It is MITOSIS (not meiosis) that leads to genetic stability because mitosis produces daughter cells that are genetically identical to the parent cell (refer to my blog post on 17 april on mitosis), unlike meiosis.
This Q is asking you why "reduction division" (ie. diploid --> haploid) needs to occur in meiosis. If i remember correctly, this was mentioned in the lecture notes. For this Q, you probably need to mention (i) how haploid gametes are formed as a result of meiosis I, (ii) how fertilization occurs to RESTORE THE DIPLOID NO. OF CHROMOSOMES, and (iii) conclude that meiosis works to PREVENT THE DOUBLING of no. of chromosomes in each successive generation.
Let me post this comment first as im afraid its too long.
4. Actually there are many more possible areas of comparison. For your benefit in the long run, I think you ought to come up with these on your own(you can write your answers down on a piece of paper and hand in for me to mark if you like). Perhaps you can also try discussing this with your friends!
Delete5. First of all, you should be able to recognise that this question is based on the topic of enzymes. I believe it is a question that has been asked a few times before. Let me rephrase it to help you understand better: why do you think some enzymatic reactions occur in a series of steps rather than in just one step? For a 6mark question, I think you have to mention three points, than elaborate each point using EXAMPLES.
I'll open this question up to everyone to contribute. :)
hi.... can u explain what are plasmid vectors? for bio olympiad... thx:)
ReplyDeleteHi Thaheera,
DeleteThis topic will be covered in a later Biology topic. But I can explain this briefly.
Bacteria such as E.coli has two types of DNA, a chromosomal DNA (a large circular DNA) and an extrachromosomal DNA called the plasmid DNA (a small circular DNA that replicates independently of the chromosomal DNA). The plasmid DNA has a small number of genes, usually coding for proteins that allow it to survive under unfavourable environments (eg. allows it to survive in the presence of antibiotic in the environment).
The plasmids can be used as a VECTOR to clone a gene-of-interest, meaning that you want to produce many copies of that particular gene. Gene cloning involves several steps, of which you will learn in detail later or perhaps in olympiad). In order not to confuse you guys, I have summarised some basic steps in LAYMAN TERMS so please don't quote me:
- Obtain the gene-of-interest from the cell (eg. a cell from a bird), and then you obtain a plasmid from a bacteria (eg. e.coli).
- Insert the gene-of-interest into the plasmid DNA (forming "recombinant plasmids").
- Put the plasmid back into bacteria to allow the genes (including the gene-of-interest) to be cloned/expressed.
The reasons why plasmids are used as cloning vectors are because:
- they can be genetically engineered/made
- foreign DNA can be inserted into plasmids to form recombinant plasmids before reintroducing them back into bacteria cells
- they reproduce very fast by repeated cell divisions (binary fission) to form a clone of cells which are genetically identical (hence many copies of the gene-of-interest is produced)
Hope this helps.