List of Figures

Plate 1.

Plate 2.

Plate 3.

Figure 1-1. Diagram of a longitudinal section of a hair. The four main hair types drawn to scale.

Figure 1-2. The early stages in the development of the hair follicle and hair.

Figure 2-1. Schematic representation of phenotypic variability of coat-color patterns among A^vy/a^m and a^m/a^m mice in Wolff's VYm stock.

Figure 2-2. Melanin granules in a melanocyte from the hair follicle of a yellow mouse (C57BL/6— A^y).

Figure 2-3. Eumelanosomes and phaeomelanosomes occurring within the same hair bulb melanocytes of a 3-day-old agouti mouse.

Figure 2-4. Metabolic pathway of eumelanin and phaeomelanin biosynthesis.

Figure 2-5. Recessive yellow ( e/e) mouse which had been partially plucked, and 5 days later had received a series of 10 daily injections of MSH; lethal yellow ( A^y) mouse similarly treated; A^y mouse which had been plucked but which received medium rather than MSH; A^y mouse similarly treated but which received MSH only on days 8 and 9 after plucking.

Figure 2-6. Histological section of the dorsal skin from an A^y mouse that had received a single innoculation of MSH 8 days after plucking.

Figure 3-1. A typical brown ( a/a;b/b) melanin granule at maturity. (b) Mature black melanin granules in both longitudinal section and cross-section.

Figure 3-2. Adult light ( a/a;B^lt/B^lt) and dark ( a/a;B^lt/b) mice.

Figure 3-3. Whole mount preparations of pigmented hairs from B^lt genotypes.

Figure 3-4. Mid-region of a light ( a/a;B^lt/B^lt) hair follicle (13th day of hair growth cycle).

Figure 3-5. Hair bulbs of a light ( a/a;B^lt/B^lt) mouse (13th day of hair growth cycle).

Figure 3-6. Hair bulb of a dark ( a/a;B^lt/b) mouse (13th day of hair growth cycle).

Figure 3-7. Hair bulb of a light ( a/a;B^lt/B^lt) mouse (10th day of hair growth cycle).

Figure 3-8. Hair bulb of a light ( a/a;B^lt/B^lt) mouse (6th day of hair growth cycle).

Figure 3-9. Whole mount preparations of light ( a/a;B^lt/B^lt) melanocytes in the epidermis of the ear pinna, sole of the foot and tail.

Figure 3-10. Hair bulbs (7th day of hair growth) from the white spotted areas of varitint-waddler ( Va/+), belted ( bt/bt), splotch ( Sp/+), and piebald ( s/s) mice.

Figure 3-11. Hair bulbs (seventh day of hair growth) from white ( Mi^wh/Mi^wh) and viable dominant spotting ( W^v/W^v) mice.

Figure 3-12. Hair bulbs from an albino mouse (7th day of hair growth) and a pink-eyed chinchilla ( A^w/A^w;c^ch/c^ch;p/p) mouse (7th day of hair growth).

Figure 3-13. Hair bulbs that developed in (a) a graft of intact somites plus neural tube taken from 10.5-day-old albino ( c/c) embryo. (b) A graft from the limb bud of a 10 to 10.5-day-old albino ( c/c) embryo. (c) A neural crest-free limb bud graft from a 10.5-day-old potentially pigmented ( a/a;b/b;d/d) embryo. (d) A graft from the limb bud of a 12.5-day-old albino ( c/c) embryo.

Figure 3-14. Melanin granules in the retina of a 15-day-old albino mouse.

Figure 3-15. Three stages in the development of the black retinal granules prepared from 20-day-old embryos.

Figure 3-16. Schematic diagram of speculative sequence of melanin formation as viewed by M.A. Lutzner and C.T. Lowrie ( 1972).

Figure 4-1. Whole mount preparations of pigmented hairs. (a) Hair from an intense black ( a/a) mouse. (b) Hair from a dilute black ( a/a;d/d) mouse. (c) Another hair from a dilute black animal but in this case showing a region containing an unusually large clump of melanin. (d) Hair from a pink-eyed leaden ( a/a;p/p;ln/ln) mouse.

Figure 4-2. (a) Hair bulb from a 5-day-old intense black ( a/a) mouse. (b) Hair bulb from an adult leaden ( a/a;ln/ln) mouse (12th day of hair growth cycle). (c) Hair follicle from a 5-day-old dilute ( a/a;b/b;d/d) mouse. (d) Hair bulb from another 5-day-old dilute ( a/a;d/d;p/p) mouse.

Figure 4-3. (a) Melanocyte from the harderian gland of a 10-day-old a/a mouse. (b) Melanocyte from the harderian gland of a 4-day-old a/a;b/b mouse. (c) Melanocyte from the harderian gland of a 4-day-old a/a;d/d mouse. (d) Three melanocytes from the harderian gland of a 6-day-old a/a;b/b;d/d mouse. (e) Nucleofugal melanocytes imbedded in the connective tissue capsule of the harderian gland of a 10-day-old a/a mouse. (f) Nucleopetal melanocytes imbedded in the connective tissue capsule of the harderian gland of a 4-day-old A^y/a;d/d mouse.

Figure 4-4. A typical nucleopetal melanocyte from the harderian gland of a leaden ( a/a;b/b;ln/ln) mouse. (b) A typical nucleofugal melanocyte from the harderian gland of a nonagouti ( a/a) mouse.

Figure 4-5. (a) Melanocytes recovered from a graft of a/a;D/D 12-day-old embryonic skin to the eye of an a/a;b/b;d/d;p/p host. (b) Nucleopetal melanocytes recovered from a graft of a/a;b/b;ln/ln 10-day-old embryonic dorsal tissue to the eye of a nonleaden albino host. (c) Melanocytes recovered from a graft of a/a;b/b;d/d 12-day-old embryonic dorsal tissue to the eye of a nondilute abino host.

Figure 4-6. Pigment granules in awl hairs of six different genotypes.

Figure 4-7. Stages in the development of a/a;p/p melanin granules.

Figure 4-8. Fresh, squash preparation of the retina and choroid from a 14-day-old nonagouti ( a/a) mouse.

Figure 6-1. (a) Cleared whole mount of a beige ( a/a;bg^slt/bg^slt) hair showing medullary and cortical pigment. (b) Cleared whole mount of a beige ruby-eye ( a/a;bg/bg;ru/ru) hair. (c) Region of a hair from a C57BL/6 ( a/a;+/+) mouse showing small, ovoid granules. (d) A similar region from a C57BL/6- bg^J/bg^J mouse showing large, irregular melanin granules.

Figure 6-2. (a) From the eye of a C57BL/6J (+/+) mouse showing that normal, small ovoid granules are present in the choroid and round and rod-shaped granules occur in the retina. (b) A similar region from the eye of a C57BL/6- bg^J/bg^J animal in which large, irregular melanin granules are present in both the choroid and retina.

Figure 6-3. Melanin granules of beige mice as viewed with the electron microscope. (a) Giant melanosome from the retina of a brown beige ( a/a;b/b;bg^J/bg^J) adult. (b) Giant granules from the choroid of a brown beige adult. (c) Mature choroidal granule from an adult beige ( a/a;bg^J/bg^J) mouse which is melanized in all areas.

Figure 7-1. Diagram of the experimental procedures involved in producing allophenic mice.

Figure 7-2. These 14 B10CBAF₁ (C/C) <--> SJL ( c/c) allophenics demonstrate the variation that can occur between animals of the same genotype.

Figure 7-3. The striped patterns which occur in these three C/C <--> c/c allophenics are the same as those which occur when the two pigmented genotypes are employed except that, on the average, half the bands are white.

Figure 7-4. Patterns realized in allophenic animals as a consequence of independently originating melanoblast and hair follicle clones.

Figure 7-5. A p^un/p^un mouse which, as a result of spontaneous somatic reversion to wild type, possess two populations of melanoblasts.

Figure 7-6. (a) A/A <--> a/a allophenic showing a typical hair-follicle clonal pattern and (b) viable yellow ( A^vy/a) single-genotype mouse displaying the same pattern.

Figure 7-7. (a) Mi^wh/Mi^wh <--> +/+ allophenic and (b) Mi^wh/+ single-genotype animal showing the same spotting pattern.

Figure 8-1. A diagrammatic representation of X-inactivation as applied to coat-color mosaicism in the mouse.

Figure 8-2. Diagrams showing dorsal and ventral sides of two typical dappled-2 females.

Figure 8-3. A young brindled ( Mo^br) male.

Figure 8-4. Brindled hairs. (a) Awl from a Mo^br/+ female (19 days), (b) awl from Mo^br male (littermate, 12 days), (c-f) other hairs from the same animal at lower magnification (all completely devoid of pigment in the segments shown).

Figure 8-5. Variation in the degree of expression of brindles ( Mo^br) in heterozygotes.

Figure 8-6. Brindled ( Mo^br/+) female, 19 days.

Figure 9-1. A diagram of the 14 primary areas proposed by Schaible (see text).

Figure 9-2. A typical piebald lethal ( s^l/s^l) mouse.

Figure 9-3. A typical piebald mouse ( a/a;s/s) of the stock employed by Mayer in his studies.

Figure 9-4. A 3-week-old lethal spotting ( ls/ls) mouse displaying spotting typical of this mutant.

Figure 9-5. Belted ( bt/bt) mouse illustrating the "belt" across the back posterior to the midline.

Figure 10-1. Mouse homozygous for viable dominant spotting ( W^v).

Figure 10-2. Dorsal and ventral views of W^f/W^f (left), W^f/+ (middle), and +/+ (right) mice.

Figure 10-3. Dorsal and ventral views of three patch ( Ph/+) mice.

Figure 10-4. Typical spotting patterns of (a) Ph/+ alone and in combination with (b) Rw/+, (c) Sl^d/+, and (d) W^x/+.

Figure 10-5. Typical a/a;Ph +/+ W^v mouse.

Figure 10-6. Typical spotting patterns of (a) Ph^e/+ alone and in combination with (b) W^v/+ and (c) Rw/+.

Figure 10-7. Dorsal and ventral views of three rump-white ( Rw/+) mice.

Figure 10-8. Typical spotting patterns of (a) rw/+ alone and in combination with (b) W^v, (c) bt/bt, (d) Sl^d/+, and (e) Sp/+.

Figure 10-9. Dorsal and ventral views of three Rw +/+ W^v mice.

Figure 11-1. Dorsal and ventral views of littermate 6-week old (a) W/+;f/f, (b) W/+;f/+, (c) +/+;f/f and (d) +/+;f/+ genotypes.

Figure 11-2. Varitint-waddler ( Va/+) heterozygote.

Figure 11-3. Dorsal and ventral views of (a) +/+, (b) Va^J/+, (c) Va/+, and (d) Va^J/Va^J mice.

Figure 12-1. [2-¹⁴C] Tyrosine incorporation in skin slices of 5-day-old mice differing at the microphthalmia locus. Means, standard errors, and the number of determinations are shown for each genotype.