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Synthesis of stocks and phenotypic effects of dwarf and bantam sex-linked major genes in egg-type chickens
Randolfo William Silvestre Custódio
Departamento de Genética, Escola Superior de Agricultura "Luiz de Queiroz", Universidade de São Paulo, Caixa Postal 83, 13418-900 Piracicaba, SP, Brasil. R.W.S.C. is the recipient of a CNPq fellowship.
ABSTRACT
The present study describes the production f stocks segregating dwarf (dw), bantam (dwB) and normal (dw+) alleles, as well as the characters, shank length, adult body weight, age at sexual maturity and egg production. Heterozygous K dw+/k dwB sires were mated to normal (dw+) dams to produce stock D6.a, and mated to dwB females to produce stock D6.b. Stock D4.a came from mating Fl heterozygous dwB dw sires to dwarf Leghorns. In a third series f matings, 7/8 Sebright and 1 /8 dw-Leghorn dw dw sires were crossed to three groups f dams f different genotypes. The progeny f the normal (dw+), dwarf (dw), and bantam (dwB) dams were designated as stocks D4.b, D4.c and D4.d, respectively. The dw+ dams were White Leghorn strain cross females. The difference between the rate f laying f normal (69.7%) and their bantam sisters (68.6%) was not statistically significant when the average 32-week body weight f the dw+ sisters was 1,897 g. However, when the 32-week body weight f the normal daughters from the same sires and smaller dams was around 1,646 g, the difference between the rate f laying f the normal (78.1%) and their bantam sisters (75.9%) was significant (P < 0.05). The dwB gene may have a similar but smaller effect on the rate f egg laying than its dwarf allele. The difference between sexual maturity f normal and bantam daughters f either the largest or the smallest dams was not statistically significant, even though the smallest dwB pullets were in average 2.9 days older at first egg. The use f shank length combined with adult body weight allowed a precise discrimination between bantams and dwarfs.
Keywords: phenotypic effects; dwarf; bantam; chickens.
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