54 votes

How does a gene "know" what to change to?

Using your example, the gene doesn't know anything. Mutations cause some of the offspring of the red frog to turn green, some to turn blue, some to turn fluorescent yellow, and some stay red. Birds ...
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Specific mechanism behind lethality of yellow coat color in mice

Really interesting question: The lethal yellow mutation (also abbreviated Ay) affects the agouti signalling protein which plays a major role in pigmentation. Heterozygous expression of it leads to the ...
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16 votes
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What is the instructional language of DNA?

This language is called the genetic code. But before talking about this specific code, it is important to talk about how the code is read. Please note that the below answer is a simplification of the ...
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14 votes

Can a blood type O be born from AB and A parents?

The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The IA allele gives type A, IB gives type B, and i gives ...
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11 votes

How to validate the regulatory interactions inferred from gene expression data?

You can validate the interactions by knockding down (KD) or overexpressing (OE) a gene and checking the change in expression levels of the downstream nodes. You can do this in a high throughput ...
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Father with mutated mtDNA- why isn't his offspring at risk?

...would then be his offspring at risk? Why? No. Generally speaking, fathers do not pass on their mtDNA (Mitochondrial DNA). Why? Because the mitochondria present in oocytes (egg cell) is the mother'...
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Can I use multiple bicistronic RBS sequences in a synthetic biological circuit?

That’s a great question and has lot of opportunities to explore. I am not sure anyone has followed up on this original BCD work systematically. We did try cloning these elements on a medium copy ...
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Do DNA repressors exist?

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 ...
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Do any RNAs directly inhibit transcription

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 ...
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Plasmid in the nucleus and gene expression

If you transfect cells with plasmid then these plasmids need to go into the nucleus (otherwise they wouldn't be transcribed). Getting the plasmid either happens during cell division (when the nucleus ...
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8 votes

Name two reasons why it is impossible to determine a gene's nucleotide sequence from the amino acid sequence of the polypeptide

I can think of at least 3 reasons in addition to the one you gave: 1: As mentioned in the comments, RNA splicing takes place on most messenger RNA encoding proteins in eukaryotes. Sections of the ...
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7 votes
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which exact mechanism triggers the first cell differentiation after n divisions?

The first differentiation in human embryogenesis is from early blastomeres into trophoblast, which forms the outer layer of the blastocyst, and inner cell mass (ICM). It may be unsurprising then that ...
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Where to find E.coli gene expression data?

There are some databases in which you can search for E.coli gene expression data: GenExpDB: E. coli Gene Expression Database Many Microbe Microarrays Database (M3D): A resource of microbial gene ...
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Lac operon: How can lactose enter the cell in the absence of lactose permease?

Introductory textbooks will not get into the details of the lac operon. Basically, the operon is expressed constitutively at a low level that means that Beta Galactosidase and Lactose Permease are ...
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meaning of the "reads" keyword in terms of RNA-seq or next generation sequencing

In RNA sequencing, the RNA is fragmented, DNA is synthesized complementary to the RNA fragments, which is followed by a complementary strand synthesis. Fragmentation can be done after the cDNA ...
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Left-handedness and Right-handedness - Are they genetic?

Handedness has, like many traits, a non zero heritability. You now should read the post Why is a heritability coefficient not an index of how “genetic” something is? to understanding what heritability ...
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Relative abundance of transcription factors and protein kinases

Summary The abundance of protein kinases and transcription factors vary among and between these broad classes of protein. General Considerations Let us first think what might be expected for the ...
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5 votes

Is the function of adjacent genes correlated?

A group of tightly linked genes that are involved in similar molecular pathway is called a supergene. For the pleasure to formulate a slight opposition to @shigeta's answer, I will give some examples ...
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Redundancy of the genetic code

Wobble pairing is just a phenomenon and not a hard and fast rule. There are some justifications for why it should exist and that is why it is still called a hypothesis. And this statement is not true:"...
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Father with mutated mtDNA- why isn't his offspring at risk?

TL;DR: Ubiquitin. Occasional occurrence of paternal inheritance of mtDNA has been suggested in mammals including humans. Clearly, spermatozoa have mitochondria; they make the energy needed for ...
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5 votes
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Can molecular genetics make a boolean variable from a continuous variable?

Positive feedbacks can be one alternative. Positive feedbacks exhibit bistability and can therefore adopt one of the two stable states depending on the initial condition. A famous example of a ...
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How much time do the different mechanisms of gene regulation need to take effect?

People often imprecisely say that type of regulation takes place on the order of many minutes to hours, and that may be as precise as you can get given the variable kinetics of any given pathway. ...
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Is the increased/decreased enzyme activity (tyrosinase) caused by an environmental factor (UV radiation) considered to be gene expression?

Unless there's a feedback mechanism shutting off gene expression (which controls the proteins made by a cell), activation or deactivation of an enzyme is not in itself a matter of gene expression, it'...
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Why are most mutations recessive?

It is a bit ironic that you phrase your question with 'in the first place'. There is a parsimonious explanation for the effect: Dominant deleterious variants are quickly removed by purifying selection ...
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Why does the pET- expression vector contain a LacI gene additionally to the one in the genome?

According to this article, a single lacI gene copy gives rise to about 10 copies of lacI protein per cell, and we can conclude, therefore, that this is the amount required to keep a single lac operon ...
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Redundancy of the genetic code

You are correct in saying that Crick, in his Wobble Hypothesis, proposed that “the base on the third position of the codon and that on the anticodon need not be complementary”, but the “need not be” ...
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Can methylation of a promoter induce gene expression in some rare cases?

There is nothing intrinsic to DNA methylation itself that requires it to repress transcription. Simply, it affects sequence recognition by proteins. CpG methylation can prevent transcription factor ...
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What network motifs or other mechanisms can make the expression of a gene invariable to the environment?

This phenomenon of being insensitive to certain fluctuations is called robustness. The fluctuations can be of two kinds for an input-output device such as a gene that is activated by a signal: ...
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Mechanism by which $lacI^{d}$ is a dominant mutation, impairing the function of normal copies of the Lac Repressor

The lac repressor act as a tetramere molecule and requires all 4 of the subunit to be able to bind DNA to act on the operon and repress β-galactosidase expression. The "all 4" is the key here, if any ...
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4 votes

Why do some protocols require prewarming a liquid medium before inoculating?

It's because E.coli BL21(DE3) are competent cells. The competent is the key here as the cells were chemically treated so the transfection can be performed by heat-shock with high efficiency. This ...
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