Hello! Can someone help me understand the concepts of blood typing: A, B, AB, O?

Question

anonymous · Answer

I have a question about whether it is possible for Mrs. James and Mrs. Walls to be sisters because Mrs. James has the possible A blood type, and Mrs. Walls has an O blood type. And what would the blood types of their parents be, if they are sisters... HELP!

anonymous · Answer

I concluded with yes it is possible to be sisters... because an A blood type can have two A alleles or one A allele and O allele.

anonymous · Answer

absolutely right.

anonymous · Answer

but do you know how I can include a Punnet square to prove this?

anonymous · Answer

the A allele is dominant over the 0 allele. both parents need to carry A0, the chances for an offspring to carry bloodtype 0 is 25%

anonymous · Answer

ohh, i see. I think I'm getting it, thank you.