Is a persons DNA likely to be more similar to the DNA of his biological parents or to the DNA of one of his first cousins

Thats a good question but tbh i think it would be closer to that of his bilogical parents because half of are dna comes from our father and the other half from our mother so i would say the bilogical parents not the first cousin

It is more likely to be similar to his/her parents because the get half of their genetic code from their mom and half from their dad.