If a child inherits two recessive genes, say one for blue eyes and one for green eyes, which trait will show?
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Generally, there is no such thing as “two different recessive versions of a gene”. Recessive variants are usually a “broken”, “inactive” or “do nothing” versions. That’s why there cannot be two of them – there is only one way to do nothing. If there appears to be two recessive variants, it usually means that multiple genes are involved (as it is in your example with eye color).
There can be two dominant variants, however. If child inherits two different dominant variants, they usually interact with each other, creating kinda a mixture of both. An example is blood type gene: it has 3 variants – dominant A, dominant B and recessive 0. Those create 4 options:
* `00` gives O blood type
* `0A` or `A0` give A blood type
* `0B` or `B0` give B blood type
* `AB` or `BA` give AB blood type
Eye color is actually determined by multiple genes (as much as 15, each having their own dominant/recessive variants) – that’s why it does not follow simple rules. But, simplified: there is one gene, that determines “brown”(dom.)/”non-brown”(rec.), and all others that mix up into all other colors. The way they mix up is not trivial.
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