Which link to Scandinavia is this? Native American genetic ancestry is strongly northeast Asian. Lot of research on this that all points to northeast Asia. For instance. There is a possible connection with the Pacific as well, but probably (pending future research) of more minor relevance to the genetics of modern Native Americans.

What may be resolved by further genetic testing (though still an open question) is how many separate migrations or population movements of people crossed into northern North America from Asia. Linguistic evidence possibly indicates three migrations, but genetic evidence could corroborate this. There were probably at least two migrations, but there are possibly more.

Seeing as how this is a genetics/evolution question, and the timescales you're going to be getting arguably stretch into prehistory, you might want to consider posting this to /r/askscience instead.

However, had a molecular evolution class last year that might provide some insight. I'll admit that I'm neither a historian, nor an evolutionary bio person, but I'll try my best to clarify anything that comes up.

Using mtDNA, Cann, Stoneking & Wilson (paywalled unfortunately), showed the outgroup of all human haplotypes is subsaharan African. That is to say, humans were there first, and everywhere else has significantly reduced diversity due to compounded founder effects (Ingman et al 2000 has a good figure showing this). There was a study done in 2002 that showed that "Within-population differences among individuals account for 93 to 95% of genetic variation; differences among major groups constitute only 3 to 5%". That is to say, the differences within a haplogroup are significantly larger than those between haplogroups.

Related to the subsaharan African-outgroup point, examining gene flow between humans and Neanderthal shows that basically all early Europeans/Asians intermingled with Neanderthals much more heavily than early Africans did (really interesting source here).

Finally (and probably the most unheard of thing in this post); neanderthals weren't the only non-human hominids that homo sapiens has mixed with. So in the Altai mountains (wedge of modern Russia between Kazakhstan and Mongolia), we found these bits of skeleton from a new species of hominid called "Denisovans". Turns out the humans with the closest relation to this group (by a large margin) are Melanesians (that is, Papua New Guinea, Vanuatu, Solomon Islands, and Fiji). And, because we know that the bones were 30-48 ky old, it's safe to say that roughly that long ago, the ancestors of Melanesians were in central Asia. Source (thankfully full freetext) here.

Genetics here: Two things for me: Neanderthals/human mixing & no Italian heritage in British Populations.

First I would say that the intermixing of Neanderthals and modern humans was surprising. For populations outside of Africa there is a 2% to 3% of each person's genome for has a Neanderthal origin. A few years ago the genome of Neanderthals was sequenced scientists then compared the Neanderthal genome to modern humans showing strong evidence of interbreeding of the populations. http://www.sci-news.com/othersciences/anthropology/science-neanderthal-genes-modern-human-dna-01734.html https://www.newscientist.com/article/dn26435-thoroughly-modern-humans-interbred-with-neanderthals/

Secondly doing mapping of British populations researchers that migration waves matched the sub-regional populations of modern Britain. However they found no DNA evidence of mixing of Italians aka the Romans from when they colonized England. In the Romanized regions there was migrations of Gauls but not Romans into south east England. http://www.sci-news.com/genetics/science-study-genetic-structure-british-population-02616.html

I'm actually reading a great book on this topic right now, it might be of interest to you. It's called Deep Ancestry: Inside the Genographic Project by Spencer Wells.