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40

I'll keep this short and simple. The direction of transcription (which determines which strand is used as the template) is controlled by the promoter, which is a region of specific DNA motifs at the 5' end of a gene. RNA polymerase binds to the promoter, which orients it on the correct strand and in the correct direction, after which it can proceed to ...


35

Going through the possible answers (A) Rates tend to be very high in most populations. This is a very unclear statement. What does "high" mean? In humans, the average mutation rate per reproduction per nucleotide is of the order of $10^{-8}$ (Rahbari et al., 2016) (hence of the order of 10 - 100 mutations for the whole genome). Whether someone wants to ...


31

There is still a lot to be learned about the roles introns play in biological processes, but there are a couple of things that have been pretty well established. Introns enable alternative splicing, which enables a single gene to encode multiple proteins that perform different functions under different conditions. For example, a signal the cell receives ...


20

Human female cells contain most of the genetic information required to make a male, but they do not contain a critical component: The Y chromosome. This is a relatively small chromosome. Wikipedia claims we have identified around 200 genes on it to date, compared to estimates of 20,000 - 25,000 genes overall in the human genome. Importantly for your ...


20

Summary: The idea that primary sexual determination defaults to female was proposed several decades ago and is primarily based on the observation that, in the absence of Sry, ovarian development takes hold. However, more recent models suggest that both ovary and testis development require complex genetic regulation and neither can really be said to occur by ...


16

A cistron is a gene - here's how the word came about: It's 1955. The proposed double helical structure of DNA has been published and the race is on to understand the implications of this for genetics. Geneticists have been working with genes for decades, but they don't know what genes are. Sanger has sequenced the two polypeptides of insulin, so the idea of ...


16

To add to canadianer's answer, in fact genes can be found on both strands of the DNA in most eukaryotic cells, in the sense that the sense and anti-sense strands are not always the same strand. The direction is therefore completely determined by the promoter. Furthermore, there are bidirectional promoters.


13

Different genes will serve different purposes. For example, if you want to perform colocalization studies, then fluorescent genes like eGFP and DS-Red (or any variation of those, namely Emerald, mCherry, etc) will be quite useful, since you can use different filters on your microscope for the various fluorophores. For morphological assessments, perhaps a ...


13

GMO foods have a huge potential to make food cheaper to produce and more nutritious. The most common GMO foods have at least one gene added to them - an enzyme that makes the plant resistant to RoundUp - an herbicide made by the same company (Monsanto). this makes the farmers able to grow their crops with much less intensive labor to keep the plants ...


13

Hanahan and Weinberg's "Hallmarks of Cancer" articles should answer your question. Their original, highly cited (14k+ citations), [Six] Hallmarks of Cancer article list these six common attributes of all cancers: Sustaining proliferative signaling Evading growth suppressors Activating invasion and metastasis Enabling replicative immortality Inducing ...


12

Short answer All mutagens are potential carcinogens unless the mutagen is highly specific to a site. As noted in the question, carcinogens need not be mutagenic. HPV causes oncogenic transformation of a cell because of certain proteins that it expresses. HPV is considered a carcinogen by the IARC. Some retroviruses are oncogenic: they might carry an ...


12

Understanding the statistics we use when talking about recombination rate is an important question that is unfortunately too often dismissed in an intro course to evolutionary biology or population genetics and that is misunderstood by many. Short answer A recombination rate and a genetic distance (in centiMorgan) are two different things. While the ...


11

A good question (if a little mixed up on transcription vs. translation!) AUG is not always the start codon, but whatever the codon is it will always code for Methionine (or fMet, but still a variation on Met), even if the codon codes for a different amino acid otherwise. A separate transfer RNA (tRNAi, the initiator tRNA) is used for the arrangement of ...


11

This question can't be answered with a simple yes/no, but I would say that the analogy of DNA being the "code" used by cells is a reasonable one, if taken with a number of other considerations. DNA function When Watson and Crick first described the structure of DNA (being a double-stranded sequence of the nucleotides Adenine, Cytosine, Guanine and Thymine)...


10

This question is closely related, and the fascinating link posted by @JohnSmith is a good read. In short, with a four-base system, and a codon size of 1, you get four possible amino acids. Silly system. A codon size of 2 gives 16. Not too shabby, but not a lot of room for growth, and not enough for those 20 amino acids. Codons of size 3 gives 64 - ...


10

Welcome to Biology.SE. if I take an X-chromosome from two random humans would I count exactly 155,270,560 base pairs in both cases No, you would probably not find the exact same number of base pairs because mutations do no only change one nucleotide to another (what we call a substitution) but sometimes add or delete few (or sometimes many) nucleotides. ...


10

According to this powerpoint from the SIU School of Medicine: Right handed supercoiling = negative supercoiling (underwinding) Left handed supercoiling = positive supercoiling And from this Boston University webpage: If DNA is in the form of a circular molecule, or if the ends are rigidly held so that it forms a loop, then overtwisting or ...


10

Yes there are reports of RNA directly inhibiting transcription. RNA induced transcriptional silencing (RITS) is a well known pathway in Schizosaccharomyces pombe (fission yeast). Initial heterochromatinization is dependent on the RNA (as a DNA identfication module) that guides other functional proteins to the target (Also see Djupedal et al., 2009). piRNA ...


9

Perhaps you can draw inspiration from classic paper on lambda cloning: Maniatis T, Hardison RC, Lacy E, Lauer J, O’Connell C, Quon D, Sim GK, Efstratiadis A. 1978. The isolation of structural genes from libraries of eucaryotic DNA. Cell 15: 687–701. Try selecting tissues from the animal which you think is "enriched" (i.e. highly expressed) for the specific ...


9

You should check out Howald C, et al[1]. This is one of the many recent papers tied to the ENCODE data. They've used RT-PCR to amplify exon-exon junctions and then sequenced the results. Supplemental table 2 shows 3076 validated exon-exon junctions in putative processed transcripts which, in the main body of the paper may be sub-classified as: Non-coding,...


9

This answer also involves some speculations as the question is about a good theoretical framework for a science fiction. You can find in this post about how sperm can be used to produce embryonic stem cells. It would still require an oocyte for doing that. The question now is- Can you produce oocytes from a male? You may fuse two X bearing haploid ...


9

The pattern we see in B. subtilis is quite common in prokaryotes. The origin of replication is shown at the top of the genome diagram. DNA replication proceeds bidirectionally from this point. In the B. subtilis diagram, most genes are located along the leading strand in each direction. Even in E. coli, by the way, important genes, including all rRNAs, tend ...


9

Yes, these sequences exist and they are called "silencers" (surprising, right?). There are different mechanisms by which this silencing of genes can happen. In the "classical" way the silencer is bound by a transcription factor which either passively suppress the gene by hindering the binding of specific transcription factors or by actively preventing the ...


9

Yes, nucleosomes are completely unwound. Histone chaperones such as FACT (for H2A/H2B) and ASF1, CAF-1, HIRA, Nucleophosmin etc (for H3/H4), associate with RNA Pol II and handle the displaced nucleosomes. As you surmised, the histone octamer complex is disassembled, into the H3/H4 tetramer and two H2A/H2B dimers. Right behind the elongating Pol II, the ...


9

The current hypothesis is that RNA came first, DNA and proteins came later. So the reason that four bases are used might be related to the initial RNA world, and then DNA just reused the already existing RNA bases in a slightly modified form. In the RNA world, all functions had to be performed by RNA. Having more bases available than two would likely be ...


9

The straight forward answer is: we don't know. We don't have any direct evidence for what happened at that time nor any completely developed and coherent theories for how it worked. The widely believed hypothesis is the "RNA World" hypothesis. RNA, unlike DNA, is capable of spontaneously folding to form catalytic molecules and thus avoids the needs for ...


9

First the MAJOR groove. This can be considered by forgetting that the two DNA strands are separate and thinking of them as merged together like a rope or an electric cable in my diagram below. The cable is wrapped around an axis, which can be thought of as an imaginary rod. One could wrap the cable tightly round the axis so it was always in contact with ...


8

There are two mechanisms of transcriptional termination in prokaryotes. The one shown here is "rho-dependent" because it involves rho, a DNA-RNA helicase that loads on and unwinds the RNA from the DNA, terminating the elongation by the polymerase. Check out [1] which shows a model for how rho multimers move through the RNA. The other mechanism involves ...


8

My attempt to find an answer has suggested that no-one knows how the DNA gets into the nucleus. This fairly recent paper reports attempts to track the pathway of DNA entry and transfer to the nucleus. Le Bihan et al. (2010) Probing the in vitro mechanism of action of cationic lipid/DNA lipoplexes at a nanometric scale. Nucl. Acids Res. 39:1595-1609 The ...


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