The phrase "it can be either" is correct and usable in written English.
You can use it when referring to two (or more) possibilities, as in: "The price of the item can be either $10 or $20."
In this notation, 0 means the corresponding gene is inactive, 1 means its active and X means it can be either one.
Later he went a little further, saying: "It's not about whether it's private or public – in that sense you're right, it can be either.
It can be either wirelessly connected to the Heat Link and your boiler, or wired if you have an existing fixed thermostat.
It can be either a side or stern trawler with an insulated hold where the fish are stored "wet," or fresh, after sorting.
Although 65% of the group's store space is now overseas, the domestic chain still generates the lion's share of group profits and Clarke wants to focus on markets where it can be either the market leader or in second place.
It can be either 'base- or tip-growth model' [20].
It can be either an organization or an individual.
By design, it can be either warm-cored or cold-cored.
It can be either a means or an end in politics.
It can be either a continuation pattern or a reversal pattern.
It can be either enhancement mode or depletion mode and the off-state current shows an even-odd oscillation.
