Under which circumstances would someone require a blood transfusion?

you'd need a blood transfusion if you have anemia, sickle cell disease, a bleeding disorder like hemophilia or cancer

pregnancy happens more and more

small, big, or no change could occur in the phenotype. it could cause something as simple as a cats ears to curl backwards or something as frighting as death. it could also occur in the protien-coding area and have an effect on that but no effect on the amino acids. what has to occur is a changing in the hox gene or the control gene.