Dang, a genetics question, and I came late to the party.
I wonder if the original question's error was in the word "phenotype" or in the numbers in the ratio. In a typical Mendelian monohybrid classic dominant/recessive F1 X F1, the phenotypic ratio would be 3:1. In the same cross, the genotypic ratio would be 1:2:1.
The only time I can think of a phenotypic ratio being 1:2:1 would be for co-dominant alleles, such as the human ABO blood types. Two people with AB blood types would have a 1:2:1 ratio of offspring, respectively A:AB:B.
Polyploidy -- fun stuff. Without polyploidy, many of our food crops wouldn't exist, including domesticated wheat, which arose from an interspecies hybrid that spontaneously doubled its chromosomes from being a sterile triploid to being a fertile hexaploid. Strawberries can be octoploid, and generally it is assumed that the more pairs of chromosomes the plant has, the larger the fruit. Having an odd-number ploidy in plants (triploid, pentaploid, septaploid, etc) was assumed to cause infertility unanimously, but I know from my geekiness about roses that many triploid cultivars have been used for breeding (the
Rosa genus contains species that are diploid, tetraploid, pentaploid, hexaploid and -- sometimes -- octaploid).
Only two mammal species I know of deviate from the "normal" diploid state -- two species of viscacha rat from South America are tetraploid.
It does have chapter summaries. You're right, I should start reading them first.
