One of the most distinctive characteristics of living organisms is the ability to reproduce. It is just this characteristic that is the foundation of our hobby, namely the breeding of birds.

Mutations are the basis of the adaptive improvement of the genetic composition of all living creatures. The mutations, which originated in the canary community, would not stand a change to survive in the natural state. The wild type is and will stay the most successful there.
There is an important phenomenon which often is seen as a "mistake" of mother nature and that is recombination better known as crossing-over. All living organisms posses recombination systems which are targeted on bringing together independent mutations originated in different individuals.
The reason for that is that certain mutations in combination with each other might be favorable for an individual. In our case the aim is not to join certain properties as well as to combine specific colour shades in one bird. If it is known that specific factors are linked on one chromosome, or just not, thus divided on two homologe chromosomes, than you may experience some unexpected results during the breeding season. The recombination after which suddenly two sex-linked mutations arrive together on one chromosome, occurs simply by the random assortment of these chromosomes into daughter cells at the first meiotic division. However, if genes are on the same chromosome, recombination requires crossing-over of non-sister chromatids from homologous chromosomes. This occurs during the first meiotic division, when homologous chromosomes are paired.
The primary function of meiosis is the regulation of the recombination and therefore crossing-over may not be considered a "mistake" because the whole system is part of the mechanism of survival of the individual while as a secondary function crossing-over also provides a means of repairing damage to the genome. Crossing-over results in an exchange of genetic material between the maternal and paternal chromosomes. Double crossing-over does occur also and make that part of the crossovers stay undiscovered.
In long chromosomes, like the Z-chromosomes, the occurrence of more than one crossing-over never leads to a crossing-over value (COV) higher than 50, in other words, if we determine the COV of specific factors, the crossover frequency will never exceed 50%.
The percentage found shows us the relative distance between two loci (factors) and in case more than two loci are involved also their position with respect to each other on the chromosome.
The crossing-over phenomenon was first discovered and described by T.H. Morgan [5]. The relative distance between two loci is therefore expressed as centiMorgan.

When I started studying colour inheritance in canaries a few years ago, it attracted my attention that there were some matters that might be very interesting to do some research on. One of these matters was the fact that there is a colour shade in existence known as "isabel", however, it is in fact a combination of cinnamon and agate, actually a cinnamon-agate.
Yet, and I have published this already a few years ago, people sometimes write about it if it is a separate mutation, but after studying this it appears to be a mutation-combination.
The first effort to map the avian sex-chromosome was done in fowls [4,6,15] and later on in Budgerigars [9,14].
Soon it became clear that sex-linked cinnamon and ino in Budgerigars map very close together, about 3 centiMorgan representing a COV of 3% (= 1:33). After some time this value was confirmed for several other psittacine species and cinnamon-inos as well as cinnamon-pallids have been found in almost all species investigated thanks to large-scaled breeding programs.
It was already obvious to me that there was a major difference in composition of the sex-chromosomes between psittaciformes- and finch-like birds because many finch-like species have produced a sex-linked pigment diluting mutation called "pastel". Such sex-linked pastel mutation is lacking completely in psittacine species which is very remarkable.
The question arose if it would be possible to investigate the relative distance between equivalent sex-linked loci in psittacine- and finch-like birds. Cinnamon and agate (the latter is homologue to pallid in psittacine species), proved to be excellent candidates for this research project, agate is an allele of satinette (ino) in canaries just the same as pallid is an allele of ino in psittacine birds and both mutations are very popular in the canary community.
In order to obtain some answers to this question the working group named "Development and Innovation in Canaries" in which I participate, made an appeal to obtain breeding records from breeders who cross-breed cinnamon and agate canaries. Two independent breeders responded so far and I find their results spectacular to such a degree that I decided to publish them.
The first breeder used 6 different cocks born in 2000 and offspring of a normal green cock mated to a cinnamon-agate (isabel) hen. All male offspring out of this mating are split cinnamon and agate linked on one Z-chromosome.
These cocks were mated to satinette-, green- and Hartz roller hens. Normally one would expect two genetically different types of hens namely normal hens and cinnamon-agate (isabel) hens. In reality 20 hens hatched from which 6 agates, 6 cinnamons and 8 cinnamon-agates. The agates and the cinnamons are the result of crossing-overs, the cinnamon-agates were expected. That makes 12 crossing-over hens out of a total of 20 which is remarkable.
A disadvantage of this type of mating is that we cannot detect possible crossing-over cocks in the offspring. We will have to wait until the next generation to see what kind of daughters these cocks will produce. However, we will never obtain reliable results because these cocks will probably also produce a high percentage crossing-overs in their offspring.
Most interesting breeding results were send to me by a German breeder. He collected breeding results from 1990 till 2002 and used cinnamon, agate, cinnamon-agate and cinnamon-satinette hens. With such matings we are actually able to detect crossing-over cocks in the offspring making the calculation of the COV much more accurate than in the previous mentioned matings.
The cocks he used were normal/cinnamon/agate, normal/cinnamon-agate, agate/cinnamon and cinnamon/agate. The most interesting matings are shown in the next table.

[1] Cole L.J. and Kelly F.J. (1919)
    Studies on Inheritance in Pigeons, Description and Linkage
    Relations of two Sex-Linked Characters.
    Genetics 4: p.p.183-203
[2] Hutt F.B. (1960)
    New Loci in the Sex Chromosome of the Fowl
    Heredity Vol.15; p.p. 97-110
[3] Lancaster F.M. (1972)
    Some Early Records of Sex-Linked Inheritance in the Fowl
    Journal of Heredity Vol.62; p.p.223-224
[4] Mc Arthur J.W. (1932)
    Sex-Linked Genes in the Fowl.
    Genetics 18: p.p.210-220
[5] Morgan T.H. (1910)
    Sex Limited Inheritance in Drosophila
    Science 32; p.p.120-122
[6] Morgan T.H., Goodale H.D. (1912)
    Sex-Linked Inheritance in Poultry
    Ann.New York Acad.Sci.Vol.22; p.p.113-133
[7] Mueller C.D., Hutt F.B. (1941)
    Genetics of the Fowl- Sex-linked imperfect albinism
    Journal of Heredity Vol.32; p.p. 71-80
[8] Onsman I. (1993)
    The Lacewing: An Enigma in Budgerigar Breeding
    The Budgerigar Journal (March Issue) ; p.p. 9-12
[9] Onsman I.
    www.euronet.nl/users/hnl/sexchrom.htm
[10]Owen A.R.G. (1950)
    The Theory of Genetical Recombination.
    Advances in Genetics 3: p.p.117-157
[11]Silversides F.G., Crawford R.D. (1990)
    Genetic Aspects of a New Mutation (Sal-s) to Sex-Linked Imperfect Albinism
    in Chickens
    Genetic Selection Evol. Vol.22 ; p.p.447-455
[12]Steele D.G. (1931)
    Studies on Inheritance in Pigeons. IX. The Chocolate-Brown Plumage Color
    Genetics Vol.16 ; p.p.532-546
[13]Sturtevant A.H. (1913)
    The Linear Arrangement of Six Sex-linked Factors in Drosophila, as Shown by
    Their Mode of Association
    Journal of Exp. Zoology 14 ; p.p.43-59
[14]Taylor T.G. and Warner C.
    Genetics for Budgerigar Breeders.
    London/Illife books Ltd (1961), (1986)
[15]Warren D.C. (1927)
    Sex-Linked Characters of Poultry.
    Genetics 13: p.p.421-433