It's not genetic breakdowns it's there race. Same way I'm black is same way they're mixed, or same way another person is white.
You can't tell a mixed person when you see one?!?? Where in Britain are you from?
Did you ever do science? Staitstics? General case?
Anyway that aside ...
Both of these Giggs brothers are "mixed race" but
only one would be seen as such and routinely referred to as such because Ryan "looks" white-white. Ryan being mixed is ignored because he "looks" white they just treat him as if he is whte. Not so his brother; Only when people are being specific about Ryan will they point out that he is indeed "mixed". Nevertheless he is not seen as being in the same racial camp as Mason by broader society. Like how mixed Boris Johnson is seen as being white in day-to-day lived experience.
Ryan
.
Rodri
With black looking mixed-race people in the UK it is similar.
If you have clear black features you willl be seen and treated as black in casual society. If someone wants to be specific they will point out the "mixed" part. Meanwhile mixed people who do not have clearly black features are seen and reated as non-black in day-to-day lived experience. And by the media.
Ross Barkley would not get the same treatment as Mason by crowds [unless they know his family background], playing in Europe despite being mixed because he doesn't look black and the way you look determines how you are treated. Racists in Russia don't care if you are 50% (Mason) or 70% black (John Barnes not mixed-mixed but has admixture look). They are gonna hate both. The press are gonna mistreat both.
They wouldn't get the same treatment by police ether. Or at job interviews.
Barkley
Kyle Walker and Ashley Cole don't get the same treatement despite both being technically "mixed race" because one is clearly of black extraction and the other not. So Cole gets treated like a black man, hated for dating that singer etc. Kyle vanishes into the background as just another gringo player despite what their generics really says.
Cole
Walker
The lesson is in the Brazil teams. Neymar is the border.
If you have more black features than him you get treated as black, less then you enter ambiguous - assumed non-black territory. Those that know like us see Neymar, Dani Alves and Rivaldo as being the same "mixed" but they don't get the same race-based treatment because some look more black than others. Rivaldo is more black than neymar genetically but that is not how causual society treats them.
TL;DR All mixed but Neymar would get followed around shops. Alves would get Arab terrorist treatment at borders. They wouldn't know what to do with Rivaldo.