Genetical studies on growth and form in the fowl. 2. The complexity of changes in skeletal proportions produced by selection.

Abstract

Comparisons of skeletal dimensions are made between adult females of four lines of fowl, selected respectively for relatively long and short shanks (HI and LI) and for high and low body wieght (HW and LW) at 10 weeks of age. It is shown that elongation of the leg in HI compared with LI is greatest in the tarsometatarsus, least in the femur. HW and LW are intermediate in this respect. There is no comparable proximo-distal gradient of elongation in the wing. HI differs from LI in a manner comparable to ectomorphy in humans: limb bones are all longer in HI but relatively (and in most instances absolutely) thicker in LI. HW is again intermediate in this respect. The nasal region of the skull is disproportionately elongated in HI compared with LI. In certain bones HI and LI differ widely in cross-sectional shape of the shaft: LI is flatter than HI in the tarsometatarsus, less flat in the coracoid and scapula. HW resembles in each case the line with the less flattened cross-section.