Understanding the ages of related fossil species aids scientists in reconstructing an organism's evolutionary history. Relative dating arranges geologic events in chronological order without requiring each event to be assigned a specific numerical age.
Since Mary has a Type A blood, she is either AA or AO while John is either BB or BO. Since both John's parents are Type AB, he can only have the either A or B as an allele and not O so he is BB. Since John can only give the B allele, all of his children must have the B allele in their blood types. So the adopted one is the child with type A blood.
Answer: crossing over
during the process of fertilization, a sperm and egg join together to create a zygote. since a sperm had half the number of chromosomes and an egg has half the number of chromosomes, when they join together the zygote had a complete diploid set of chromosomes. the assortment of chromosomes and crossing over promotes genetic variation during the process of reproduction
