It’s in the blood!
In conversation, we use the metaphor of ‘blood’ to mean inheritance (the Bible does too). For instance, we talk of ‘bloodlines’ in dog breeding, being of the ‘same blood’, etc. Actually, in reproduction, no blood is passed along at all. Reproduction is basically the transmission of a message, a program, carried on the DNA in egg and sperm. The information from parents is used to make all the physical components of a developing child. This includes our blood, which is constructed ‘from scratch’, from raw materials, as it were, following the ‘blueprint’ inherited from our parents.