The Kerry Babies boiled to the surface this week because someone decided to look at the DNA evidence . . . 34 years after the necessary tissue samples were gathered. That showed conclusively that Joanne Hayes, despite confessing to his murder in elaborate detail, was not the mother - not even a close relative - of Baby John whose body was washed up on a beach near Caherciveen. Sufficient details of the events in Kerry in 1984 can be found in The Indo. Indeed even back in 1984, the dogs in the street knew that Joanne Hayes could not have been the mother of Baby John because he was blood group A but Ms Hayes, her own dead baby and the baby's father were all blood group O. I think we can be sure that if Baby John had also been blood group O, then Joanne Hayes and/or members of her immediate family would have been convicted and imprisoned and the relevant Gardai would have been congratulated on a brisk and efficient investigation.
bizarre and unlikely events to be true. Let's look at the numbers. If you have no idea how ABO blood groups work, I refer you to my tutorial on the genetics. Today's investigation is about probability and gene frequencies which I've looted from George Dawson's famous survey of Irish blood groups from the 1950s, which I've cited before. Each of us has two copies of the ABO gene - one from The Mammy and one from The Dad. If you tally up a bunch of them as A, B or O and divide by the total number of genes counted, then you can calculate the frequency of each variety in Ireland [see chart L]. You can see that blood group B at 7% was very rare in 1955 and also in 1984 a generation later. It's a bit higher now insofar as we've welcomed people from *istan and the PRC where this variant is much more common [see map in my prev cited tutorial]. To be blood group O you must have inherited O genes from both parents. But there are two ways you can be B - either with one B gene or with two - pedantically but necessarily for the maths to work there are really 3 ways you can be B - BB, BO or OB. Similar arguments apply to those who are blood A. Finally you are group AB if you get A from The Mammy and B from The Dad = AB or the other way round BA. This is no discernable difference between the two cases except their history.
Many people get a bit confused about the gene frequency and the frequency of the blood groups. It's mostly because manifestation of a particular blood group - called the phenotype - depends on the presence of two variants of the ABO genes. You can verify from the table above that the chance of being blood group O depends on independently acquiring two copies of the O gene:
0.738 x 0.738 = 0.545So that's how close Joanne Hayes got to being convicted. All other things being equal, 54.5% of Irish people, including murdered neonates, are going to be blood group O. It's like Fortuna tossed a coin and it came down heads-for-exoneration rather than tails-for conviction. Phew!
Well, at that stage I got an attack of the datas and put together a comprehensive study of ABO blood groups as they impinge on paternity testing. Apart from the odd cock-up with wrist-bands in maternity hospitals we know who is the mother. The following tables and charts are based on the frequencies found in Ireland, the conclusions will be slightly different if you come from elsewhere in Europe and quite a bit different if you're tracking Aztecs or Han Chinese. First lets look at when a man and a women love each other very much . . . and have a child. We can calculate how many of each sort of mother-father-child triplets we can expect. The numbers in the coloured part of the table are the product of the frequencies along the table margins:
- If you are group O, neither parent can be AB
- If you are AB you cannot have a child who is group O
- If one parent is B and the other A then any sort of child could be legitimate
- If one parent is AB and the other is O then none of the children will be like their parents