. B6 BB B6 B6 b + b Appearance. All Andalusian ( = Fi) Black (25%) 1 Andalusian (50%) White (25%) (=F2). proportions in which the different sorts occur. In subsequent generations the F2 whites will breed true like the original pure white strain, the blacks breed true like the original black, and the Andalusians will give the same results as their Fi Andalusian parents. Another character in which breeds of fowls may difier is the shape and size of the comb. If two breeds, one with the ordinary high comb (so-called single comb), the other with a rose comb (a low comb with httle warts on it), are
. B6 BB B6 B6 b + b Appearance. All Andalusian ( = Fi) Black (25%) 1 Andalusian (50%) White (25%) (=F2). proportions in which the different sorts occur. In subsequent generations the F2 whites will breed true like the original pure white strain, the blacks breed true like the original black, and the Andalusians will give the same results as their Fi Andalusian parents. Another character in which breeds of fowls may difier is the shape and size of the comb. If two breeds, one with the ordinary high comb (so-called single comb), the other with a rose comb (a low comb with httle warts on it), are crossed, we shall get results precisely similar to those found in the Andalusian fowl. The second, or F2, generation will consist of 25 per cent, of birds which will breed true to single- comb shape, 25 per cent, which will breed true to rose-comb shape, and 50 per cent, which will contain one factor for each of the two comb-shapes, and there- fore will not breed true. The question immediately arises, What will happen if a white bird with a single comb is crossed with a black bird with a rose comb ? Will the white colour and single-comb shape stick together, or shall we be able to separate and recombine them ? The answer given by experiment is that recombination is possible. In the F2 generation, we shall get two new pure- breeding types—white birds with rose combs, and black birds with single combs—as well as t}'pes like the original parents, and types that do not breed true. Similar results have been obtained by the hundreds of thousands of crosses which have been made during the last twenty years with Mendel's principle in mind, and we can assert, wdthout any fear of contradiction, that for the majority of characters which go to make up any species or race of animal or plant, and to mark it off from other species, the fundamental laws laid down by Mendel hold good. To be brief, we may say, first, that all the characters of a species are controlled in their development b
Size: 2618px × 1909px
Photo credit: © The Bookworm Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookleafnumber269, booksponsoruniversityofto, booksubjectscience
