I know about the blood types, which ones are which, and I know how to fill out a Punnett Square, but how do you turn Ao and Bo and such from a genotype to a phenotype?

1 Answer
Nov 26, 2017


The idea of the "phenotype" is that it is how your genes (your genotype) makes you LOOK.

Phenotype is defined as "the observable characteristics" of an individual that result from its genes (its genotype ).


You don't "turn" the genotype into the phenotype.
You try to use logic to deduce what its genes (its genotype) must be given its phenotype (appearance) for that one trait.

The phenotype is the way the organism's genes make it appear, even if we don't know its genes (its genotype.)

For example, people whose PHENOTYPE is "blood group B" can have either one of these two different GENOTYPES:

1) BB genotype #rarr# phenotype is "blood group B"

2) BO genotype #rarr# phenotype is also "blood group B"

By testing a person's blood for their blood group, you can find out if their phenotype is group A or group B or group O.

But you can't tell just from the lab test if a person whose phenotype is for example blood group B has a genotype of BB or BO.

The genotype is the actual two alleles (genes) for a specific trait.

Sometimes just looking at the phenotype (the observable features of an individual) is enough to tell you its genotype (its two alleles (genes) for that trait.)

For example, a person whose blood group showed up in the lab as the phenotype AB would necessarily have a genotype of AB
~ One gene for A
~ The other gene for B

But you can't always know the exact genotype (the 2 specific alleles) just by looking at the phenotype (the outward appearance).

For example, a person whose phenotype (appearance) is "brown eyes" could have either one of these two different genotypes:
BB #rarr# both genes for Brown
- or -
Bb #rarr# one dominant gene for Brown masking the recessive gene for blue

On the other hand, a person whose phenotype (outward appearance) is "blue eyes" must necessarily have the genotype
(pair of alleles) which are bb.

It's obvious that a person whose phenotype is "has blue eyes" cannot have a dominant gene for Brown, because it would show up in that person's phenotype as Brown.

.... BB ............... Eyes look brown
.....Bb ................ Eyes look brown (because Brown is dominant)
.....bb .................Eyes look blue (no Brown gene could be there)