The Edge of Doom Read Free Page A

hand.
    The results had arrived at his office in the afternoon, and he handed the printout to Kate as soon as he was inside the door. She had been loitering about near the front door, expecting him, unable to settle to anything or even to stay seated in one place. Banny, regarding her with an obviously troubled expression, turned her head from side to side as though watching a tennis match.
    When Reed arrived to find her at the door, he looked as troubled as the dog. “For God’s sake, Kate,” he said, taking off his coat and reaching into his briefcase, “don’t you think you’re overreacting just a bit?”
    “Of course I’m overreacting, and what’s more, I don’t know why I’m overreacting. What possible difference can it make, over half a century later, if I turn out to be the result of one sperm instead of another, or if my mother, whom I thought of as the height of conventionality, and who was, after all, born not that far from the last century, was screwing around?”
    “All right,” Reed said, “what difference is it making, or threatening to make?”
    “I haven’t a clue, so don’t ask. My questions are rhetorical. Where’s the damn report?”
    Reed handed it to her. “Let’s sit down,” he said. “The answer to my question is clear enough, though the explanation is hard-going, becoming quite complicated and esoteric.”
    Kate took the sheet of paper from Reed, and sat down to read it. She did not put her feet up. He saw her read through it and then begin again. The doctor had clearly considered Reed’s request about the man’s being a possible half brother to Kate as the substantive question. If the man were indeed the father of the woman in question, he had told Reed, there would be no doubt about it. He had further written:
    “It is possible to discern a father-daughter relationship from a half brother–half sister relationship. First, consider the X chromosomes.”
    Kate made what she hoped was an intelligent effort to consider the X chromosomes, before deciding that this was a waste of time. She read on; the doctor had decided to use himself as an example:
    “My daughter has two X chromosomes. One of them comes from me, and one comes from my wife. If my daughter were in fact my half sister and we shared the same father, as in the case you are asking about, it would not be possible for her to have the same X chromosome as me, because I inherited my X from my mother, who is unrelated to her.”
    Kate looked up. “Yes,” she said, “I think I’ve got that. More or less. This reminds me of Charles Sanger’s demonstration that Emily Brontë really knew inheritance law when she had Heathcliff inherit everything from both families.”
    “I’m glad to see you’re sounding more like yourself,” Reed said. “When you mention literature, I know sanity is not far away.”
    Kate read on: “The answer for the twenty-two other chromosomes, called autosomes, is more complicated but also definitive. Sorry about the techno-speak, but it’s the only way to be accurate. Here goes: For a given pair of alleles carried by my daughter, it is certain that one of them comes from me. If she were my half sister, there would be a 50 percent chance that the allele she inherited from our shared father is not the same allele that I inherited from him. If we consider allelic pairs from each of the twenty-two autosomes, there is only about a one in 4.2 million chance that my half sister and I would inherit the same twenty-two alleles from our father. So if you assess RFLPs at twenty-two loci, one on each autosome, and find that in all twenty-two cases the woman and man share an allele, then she is his daughter to a certainty of one in four million. Another way of looking at this is that in the father-daughter pair, the daughter has half of the father’s DNA, while in the half-sibling case, the two each have half of their father’s DNA, but not the same half.”
    “What is an RFLP?” Kate asked.
    “I