Mr Lilipup has worked this out after too much Postman Pat!
My 2 year old has become obsessed with Postman Pat. I have been a reluctant observer of the programme, but I have noticed something of great interest. I do not believe Postman Pat has been limiting his deliveries to mail sacks....
Pat is a ginger, redhead, etc. The ginger hair colour is a recessive gene* and in genetics genes are described as two components denoted by letters. A capital letter denotes a dominant gene, and a lower case letter denotes a recessive gene. In any mix (ie dominant and recessive) the dominant gene is expressed. (There are other types, co-dominant etc...not relevant in this case).
Thus, the ginger gene would be GG, Gg, or gg. But the ginger gene would only be expressed in the "pure recessive" combination, ie gg.
As we all know, genes are passed on by mating. One gene letters pair is combined with another gene letter pair (one from each) to give a new gene letter pair (each letter known as an allele, but let's forget that!).
Thus GG plus gg could give only GG or Gg (both dominant); GG plus Gg could give GG or Gg (both dominant), Gg plus Gg could give GG, Gg (both dominant) or gg (recessive) and so on. In the case of gingers, only the gg result would be expressed as ginger hair because this is a recessive gene. This can only arise through the first generation mating of a mixed ginger (Gg) with another mixed ginger (Gg) or two gingers (gg plus gg) and can never arise through the first generation mating of a dominant ginger (GG) with either a mixed ginger (Gg) or a pure recessive ginger (gg).
As ginger is only expressed through the pure recessive gg, the only way of a guaranteed ginger child is through two gingers mating. If a ginger mates with a mixed non-ginger, then the chances are 50-50 that the child will be ginger (one will always be G, the other either G or g). If two non-gingers mate, then
Now, I have noticed a disturbing over-representation of ginger children in the programme, certainly when compared with parents. Pat is the only pure ginger. I believe that Postman Pat is the father of both Bill Thompson (parents Dorothy and Alf are both brunette) and of Sarah Gilbertson, daughter of the doctor (blonde and unmarried). Statistically, there is a 1 in 4 chance of a ginger resulting from the union of Dorothy and Alf, as opposed to a 50-50 chance of a ginger being sired out of wedlock by Pat "on his rounds"
Pat - you randy old git!
- (on chromosome 16 - the alleles Arg151Cys, Arg160Trp, Asp294His, and Arg142His on MC1R are shown to be recessives for the red hair phenotype),