Animal genetics / Frederick B. Hutt.

  • Hutt, Frederick Bruce, 1897-1991.
Date:
[1964]
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Animal genetics / Frederick B. Hutt. Source: Wellcome Collection.

    52/578 (page 30)
    30 ANIMAL GENETICS Karakul type of coat were caused by a single dominant gene for which that sire was heterozygous, we should expect a ratio of 6 : 6. By tests to be considered later, one finds that the observed numbers do not differ significantly from those expected, so, pending further information, we conclude that the Karakul coat is probably caused by a dominant gene. Ш—I—® - Q ^ Ò á à g a □O# X òóééóòéóòòóò ф CURLY FEMALE О NORMALFEMALE H CURLY MALE Q NORMAL MALE FIG. 2—6. Pedigree of curly coat in Ayrshires, illustrating standard methods of designating generations and individuals and of showing sexes, normal and affected animals, and their relationships. (Redrawn from F. E. Eldridge et al. in J. Heredity.) With this information from the pedigree, the breeder knows that if he wishes to retain the variant form he can get more curlies by crossing curly X normal. On the other hand, if the curly coat is con¬ sidered an undesirable defect, it is necessary to eliminate only the curlies and none of their normal siblings ( brothers and sisters ). Pedigrees Showing Recessivity. A different genetic basis is evident for two almost completely hairless calves bom one year in a small herd of Guernseys (Fig. 2-7). Although their pedigree is compara¬ tively short, there is enough of it to show how the causative gene was transmitted (Fig. 2-8). The sire (III-3) and the two mothers of the hairless calves (III-2 and IV-2) all had normal hair; the defect is therefore clearly recessive. The normal condition is domi¬ nant. As the difference between hairless calves and normal ones was extreme, without any intermediate forms, it seemed most likely that the condition was caused by a recessive gene in the homozygous state. A calf could be homozygous for hairlessness only if it had