Recent comments in /f/askscience

Fenrisvitnir t1_j5htmhk wrote

Reply to How do we know how old viruses are? by Darth_Fatass

One method:

(1) We can measure genetic drift rate of DNA.

(2) We can find partial or whole retro viruses encoded in DNA of animals such as humans because they insert themselves during replication.

(3) We can compare the viruses of today to the encoding of the virus in the DNA, and we know the age of the DNA due to the drift rate in (1). We can also therefore determine the age of the virus at time of insertion.

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Another method:

(1) Measure the mutation rate of similar viruses.

(2) Find old instances of the viruses from known prior historic periods.

(3) Compare the RNA patterns to find the mutations.

(4) Calculate the approximate age based on the mutations.

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Many other methods exist, and generally they line up. Reading:

"Yet, over recent decades it has become apparent that viruses occasionally leave a historical record in their host's genomes in the form of endogenous viral elements (EVEs)"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5962544/

LTR sequence divergence rates:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048862/

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Alittlebitmorbid t1_j5hshu2 wrote

Reply to Can you scan a brain and diagnose a mental disorder? by friday_panda

Yes, you can, but not everything and not always. CT scans can show that certain brain areas are underdeveloped which can lead to symptoms like depression, psychopathy (not sure, what the exact term is, there is always discussion about what to call it) or others. Also the brain has a huge capability of taking over the functions of damaged areas in other areas, so just because it might look heavily damaged it does not always concur with the clinical representation of the patient. There can literally be patients with half a brain and you would not notice apart from their brain scan. Have seen such cases myself. One of them was a miracle to the neurologists because he was a skilled worker at a bank and had a healthy family life with nearly no brain.

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Any-Broccoli-3911 t1_j5howpz wrote

Reply to comment by Indemnity4 in Why cant C2 exist, if carbon is tetra valent and forms bonds with other carbon atoms ( not 4 though) ? by [deleted]

MO theory says it's a double bond while VB theory says it's a quadruple bond. It's still controversial.

https://mappingignorance.org/2013/05/22/c2-molecule-doubly-or-quadruply-bonded/

https://en.m.wikipedia.org/wiki/Quadruple_bond

In MO theory, there are 2 pi bonds from the px and py electrons.

The s electrons and the pz electrons (z is the axis along which the carbons are) can be considered to have a sigma bond and an anti-sigma bond, but having both a bond and an anti-bond is the same as having no bond.

So the total bond order is 2.

In VB theory, they have 3 regular bonds plus a weak one.

Wikipedia also says:

"Quadruple bonds between atoms of main-group elements are unknown. Molecular orbital theory shows that there are two sets of paired electrons in the sigma system (one bonding, one antibonding), and two sets of paired electrons in a degenerate π-bonding set of orbitals. This adds up to give a bond order of 2, meaning that there exists a double bond between the two carbon atoms in a dicarbon (C2) molecule. The molecular orbital diagram of diatomic carbon would show that there are two pi bonds and no sigma bonds. However, a recent paper by S. Shaik et al. has suggested that a quadruple bond exists in diatomic carbon,[7] but this is disputed.[8]"

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Indemnity4 t1_j5hlhek wrote

Reply to comment by RunagateRampant in Why cant C2 exist, if carbon is tetra valent and forms bonds with other carbon atoms ( not 4 though) ? by [deleted]

> C2 alone isn’t possible

Sure it is, in the gas phase! Diatomic carbon is represented as :C=C:. To get deeper into MO, it exists in both singlet and triple forms.

What is a little bit more complicated is quadruple bonded carbon. It does appear it can have a forth order bond to another carbon atom (tetravalent), but it is in the form of a pi-bond and two sigma-bonds.

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