Some aspects of gene dosage in N- type sheep

Abstract

The dominant and recessive mimic genes N and nr produce increased birthcoat hairiness in New Zealand Romney lambs. This hairiness has been studied in lambs of different genotypes by three different methods. It has been found: (i) that in individual lambs there is a gradient in hairiness from the shoulder patch to the britch; (ii) increases in hairiness with increasing dosage of the N and nr genes conform to this gradient; (iii) with any single increase in N-gene dosage there is a differential rate of increase in hairiness on different positions. These results are explained on the hypothesis that the primary gene action is linear, but the gradient is modified by a threshold and possibly by a ceiling effect in the production of birthcoat medullation.

Birthcoat–adult fleece relationship: a study of kemp succession in a coarse wool breed of sheep

“…HH grade within animals, showed positive correlation (P < 0-01) with O x kemp (Table 8). This agrees with the interpretation of many workers (Dry, 1940;Schinckel, 1951;Stephenson, 1956) that the halo hairs may be followed by kemp or very objectionable coarse hairy fibres and that the presence of halo hairs depends upon heriditary factors. Hence, selection against halo hairs has proved very effective (Dry, 1933).…”

“…Fibre types were counted and arrays identified (Dry, 1933(Dry, , 1934. Birthcoat fibres were classified into three groups (Dry, 1933(Dry, , 1934Stephenson, 1956) on the basis of their tip curl. Pre-curly tip fibres (Pre-CT) start with a sickle-shaped tip, curly tip fibres (CT) begin with an ordinary curl and histerotrichs (Hist.)…”

“…The base is suggested as the product of a basic drive towards production of fibre coarseness and medullation; the check as an inhibiting force tending to fineness and the prevention of medullation. Dry (1933Dry ( , 1934 and Stephenson (1956) described in detail the features of the different fibre type arrays, from which the following brief summary is included: (a) plateau arrays (P), all have HH, and no SK fibres are present. There are different types of plateau arrays according to the presence of different types of SS fibres.…”

Crossing Merino and a coarse wool breed of sheep; a study of the birthcoat of lambs

“…The base is thought of as the product of a basic drive towards production of fibre coarseness and medullation; the check as an inhibiting force tending to fineness and the prevention of medullation. Dry (1933Dry ( , 1934 and Stephenson (1956) described the details of fibre types and fibre type arrays, from which the following brief summary is included:…”

“…Birthcoat fibres were divided into three groups R. A. GUIRGIS (Dry, 1933(Dry, , 1934Stephenson, 1956) on the basis of their tip curl; while pre-curly tips (Pre-CTs) begin with a sickle-shaped tip, curly tips (CTs) start with an ordinary curl, and histerotrichs with no definite shape but a straight tip. The first two groups commence their growth before birth whereas the third begins to grow about the time of birth and later.…”