Copyright is owned by the Author of the thesis. Permission is given for
a copy to be downloaded by an individual for the purpose of research and
private study only. The thesis may not be reproduced elsewhere without
the permission of the Author.
GENETIC STUDI~"S OF A DARKENING OF TITE DORSAL
COAT IN AGOUTI MICE.
A Thesis presented to the University of New Zealand in partial fulfilment of the
requirements for the de2ree of Master of A.;ricul tural
Science.
D. A. L VANS
M.A. C. 1962
ACtNOWL:-..00.EMENTS
The candidate wishes to record his indebted:ne~-s to Dr.
F. Cockrem (Sheep Husbandry Department) whose continued. iuidance and interest made this study possible.
He also wishes to ackncwledae the advice and assistance ot
Professor A.L. Rae of the Sheep Husbandry Department in which this study was carried out.
Special thanks are also extended to
: .1r. T.s.
Chana (She€pHusbandry Department) for assistance with statistical problems, and
Mr. B. Reynolds (Veterinary Science Department) for advice on histol°"ical techniques.
Finall.r, tha .ks are due to Mias .Vi..G. Campbell (Librarian; am her staff for assistance in obtainini references.
TABLE OF CONTENTS
IN J.RODUCTION
Illi'VIEW OF LITERATURE I. The Hair
(A) Development and Growth {B) Time Relations
II. The Piament {A) Biology (B) Biochemistry
1. Melanin Synthesis 2. The Me lanocyte
3. Melanin Synthesis in Relation to
1 1 1 5 4
4 6 6 7
the Hair Cycle 7
4. Yellow Pigment III. Baclc,iround Genes
(A) Aaouti Alleles
1. Description of Alleles 2. Physioloiy of Alleles (B) Dominant White
IV. Umbroua Genes
I. Introduction l l . MatiniB
lll.Reaulta IV. DiscusaiOJI
I. Experimental Tecb.niquea (A) Available Techniqaa {B) ProcedQre Adopted
10 10 10 15 16 19 22 22 23 24
27 30 30 :50 M
Paae
n.
Genetic Results based on Visual Seareiationa 48(A) Introduction 48
(B) The Ma tings and Visual Reaul ts 49
1. Homozyaoua Aaoutia 49
2. Heterozyaoua Aioutia 54 5. Homozyaous & Heteroznous Aioutis 60 4. The "Vt ry Dark" ~enotype 64
(c) Conclusions 66
III. Results based on Objective Measurements of
the Dark Phenotype 68
(A) Introduction 68
(B) Statistical Analyses 69
(c) The Dark Gene in Relation to Le!lith of
the Yellow Agouti Band 69
1. The Dominant \'ihi tes (Mi"b/+) ot
Matings Mi.1-5 69
(i) Method of Analysis 69
(ii) Results 71
( iii) Discussion 74
(iv) Conclusions 75
2. ICa tine Mi. T 77
(1) .Methods of Analysis
.,.,
(ii) Reaults and Diaoussio 81
(iii) Conclusions 85
~ Katina U.1 8"I
(1) Methods of Analy-sia 8?
(ii) Results and Discassian 8"I
4. The Effects of the Dark Genotypes on the lenath of Yellow ~lament
(i)
Introduction(ii) Results and Discussion ( iii) Conclusions
5. Pleiotropic Studies of the Dark Gene (i) Introduction
(ii) Methods of Analysis (iii) Results and Discussion (iT) Conclusions
DISCUSSION AND CONC, ,USIONS
BIBLIOOHAIBY
Paie
92 92
92 95
96 96 96 98 113
115 121
LIST OP F I ~
FACINj PII~
F1,aure 1. The pathway of melanin synthesis
6
2. The melanocyte cell ~
3. The yellow-black p~ment "switch"
,o
4. A typical aaouti ziizna hair
II
5. The ancestry of the first dark mice
,1.2..
6. The oriiin of the "dark" line
23
'1. The samplina position
.15
a .
Relationships between the variables C, Y, Ic, ( 0-1), B & 1..'/8
9. S~iested pleiotropy of the dark ~ene
//If
(i)
INTRODUCTION
It is the candidate's contention that an understandirli
ot
themechanisms of iene action and interaction at the physiol()iical level, is a necessary basis for a fuller undc rstandirli of the principles and problems of animal breedi~. On this point, Rae (1958) states ••• "pop- ulation aenetics deals essentially with i enes and final phenotypes, but has little to say about the vast developmental i&P between the two".
However,opportunities for physioloiical studies of simple Mendelian traits in farm livestock are few and far between, while the expense of such
stooies is normally prohibitive.
Consequently, physiological ienetic studies are normally carried out on small animals, especially the mouse. Gruneburi (1952) has
revie~ed the use that has been made of this mammal for ienetic studies of all types.
The steadily increasllli number of reported mutants affectin.; hair 2rowth and piamentation in the mouse provide excellent experimental
material for studies on ~ene action, while theirpleiotropic effects provide material for studies on the physiolou and development of hair irowtb. As Chase (1954) has pointed out, in the one hair follicle can be seen all aspects ofcal l development, arowth, division, and death at ditterent st&ies of the hair cycle. The hair i taelf provides a permanent record al0:qi its lenatb of the chanaes that have occurred in the hair follicle durina tbe period of hair arowth (Ruasell, E.s. 1946).
Tb studies to be described concem attempts to inveatiaate yet another ot tbeae mouse hair mutants.
