Does a genotype have to display a phenotype?

I am no genetic expert, but I believe this can happen. For example, two humans can have brown eyes. This would be their phenotype. One person could have an allele for brown eyes and an allele for blue eyes, but because the allele for brown eyes is dominant, this is the phenotype. the other person could have two alleles for brown eyes so obviously this is the phenotype that would be expressed. They have the same phenotype and different genotypes.

god I so knew this a year ago…

Thats a very good answer, but it’s not exactly what I’m looking for.

If there’s 2 birds and they look identical from the outside. Their beaks, feet, feathers and everything that can be observed from outside is the same. A test is done on both birds and it is discovered that they are different species. Is this possible?

It’s possible, but extremely unlikely. Think about the way in which DNA becomes a trait:

1. DNA is a sequence of nucleotides (AAATTCCGATCG . . . )

2. These get turned into RNA (UUUAAGGCUAGC . . . )

3. In this RNA, each group of three nucleotides codes for a particular amino acid. But if you do a little math, you will notice that in the first position, you can have any of four nucleotides (A, U, C, or G). In the second position, you can have any of four nucleotides again. And in the third position, you can have any of the three nucleotides again! So that means you have:

4×4 x 4 = 64 possible combinations of nucleotides. But we only have 20 amino acids!!!! What this means is that different combinations of nucleotides can give you the same amino acid!!!!! (This is called “degeneracy.”) So, for instance, tyrosine can be built by RNA that goes “UAU” or “UAC.”

So we have gotten as far as going from DNA to RNA to amino acids.

4. The amino acids form proteins…

5. ...and the proteins twist and coil together in just the right way to give you….pretty much everything in your whole body.

SO! If you have the right degenerate amino acids, you could have a different DNA sequence coding for the same amino acids, which could give you the same proteins, which could give you the same trait. But consider that not all amino acids are degenerate, so you can’t just run around substituting left and right.

The likelihood of this working out in nature to strikes me as vanishingly small. But you could probably build it in a lab just for kicks, if you had about a thousand years of free time.

Did that make sense, and was that at all what you were thinking of, or did I just go off on a ridiculous tangent?

That makes a lot of sense. Thanks for helping me understand this. I spent all day thinking about this because I overheard a stupid conversation waiting in line for coffee about a racist subject that I won’t mention.