Mendelism / by R.C. Punnett.

  • Punnett, Reginald Crundall, 1875-1967.
Date:
1911
Catalogue details

Licence: In copyright

Credit: Mendelism / by R.C. Punnett. Source: Wellcome Collection.

    183/210 (page 153)
    occasional appearance of a sport in a supposedly pure strain is often due to the reappearance of a recessive character. Thus even in the most highly pedigreed strains of polled cattle such as the Aber- deen-Angus, occasional individuals with horns appear. The polled character is dominant to the horned, and the occasional reappearance of the horned animal is due to the fact that some of the polled herd are heterozygous in this character. When two such indi- viduals are mated, the chances are i in 4 that the offspring will be horned. Though the heterozygous individuals may be indistinguishable in appearance from the pure dominant, they can be readily separated by the breeding test. For when crossed by the recessive, in this case horned animals, the pure dominant gives only polled beasts, while the hetero- zygous individual gives equal numbers of polled and horned ones. In this particular instance it would probably be impracticable to test all the cows by crossing with a horned bull. For in each case it would be necessary to have several polled calves from each before they could with reasonable certainty be regarded as pure dominants. But to ensure that no horned calves should come, it is enough to use a bull which is pure for that character. This can easily be tested by crossing him with a dozen or so horned cows. If he gets no horned calves out of these he may be regarded as a pure dominant and thenceforward put to his own cows, whether horned or polled, with the certainty that all his calves will be polled. Or, again, suppose that a breeder has a chestnut mare and wishes to make certain of a bay foal from