Genetics is the science of heredity which studies the transmission of anatomical, cytological and functional characteristics from parents to their offspring. In more common terms we can say that it is the science that studies the transmission of genes (mutant or not) in living beings. The first laws of genetics were identified by Mendel in 1865.
A mutation is a sudden and always hereditary change that occurs in all living things.
There are lots of mutations and composite varieties (combinations of mutations) in many species of Psittacidae including among others; the Agapornis (Lovebirds); roseicollis (peach-faced alias facepêche), fischeri (Fischer`s), personatus (masked), Neophema (Euphemas); elegans (Elegant Parakeet), pulchella (Turquoise Parakeet), splendida (Splendid Parakeet), Platycercus (Platycercus a.k.a. Rosella; eximius (omnicolor), elegans (Pennant), palliceps, Cockatiel parakeet, Budgerigar, Psittacula k. manillensis (Ring-necked parakeet -indienne), Neopsephotus bourkii (Bourkes Parakeet), Psephotus haematonotus (Red-rumped Parakeet), Forpus coelestis (Celestial Touïs), Bolborynchus lineola (Catherine’s Parakeet)…
A mutation is always transmitted hereditarily and genetically; we cannot therefore “create” a mutation or a mutant gene but we can on the other hand isolate the mutant gene following its sudden appearance (in breeding or in nature) by reproducing it according to its own mode of transmission. All mutants are either heterozygous (single-factor = sf = 1 mutant gene) or homozygous (double-factor = df = 2 mutant genes) and all mutant genes are genetically transmissible according to one of the three main known modes of transmission:
It is a mutation of genes on sex chromosomes commonly referred to as sex-linked recessive. In birds, compared to humans, the sex chromosomes are reversed: that is to say that here it is the male who has 2 complete chromosomes named XX while the female has 1 complete X chromosome and 1 incomplete Y (on which none genetic information can never be transmitted)
Here 1 heterozygous male (1 mutant gene) is non-visual for the mutation and commonly referred to as an asymptomatic carrier or mutant. 1 homozygous male (2 mutant genes) is visual for the mutation. Females, since having only 1 complete sex chromosome where genetic information is present (mutant gene (s) or not) will always be visually what is written on their complete sex chromosome (X) and therefore always heterozygous when mutant since its incomplete sex chromosome (Y) cannot contain any genetic information. On the other hand, this last chromosome (Y) is absolutely not useless since it is responsible for determining the sex of the bird which is then always female.
It is a recessive gene mutation present on autosomes or genes containing DNA. Here the two sexes (male and female) can be heterozygous (1 mutant gene = carrier = non-visual = asymptomatic) or rather homozygous (2 mutant genes = visual) since they are not mutant genes present on the sex chromosomes but of course on the autosomes with which both sexes are equally endowed.
It should be noted that the Type-Sauvage (natural color) is always dominant on the recessive mutant genes (autosomal or linked to the sex) except in the only case of 1 homozygous male linked to the sex since all his female offspring inherit the one or the other of its 2 mutant genes and then automatically visually become the mutation inscribed on their complete sex chromosome (X)
Here is an example of a cross involving a recessive-autosomal gene mutation;
Type-Sauvage X recessive-autosomal (visual therefore 2 mutant genes): 100% offspring Type-Sauvage / recessive-autosomal
or with a known mutation: Green X blue: 100% Green / blue (visually Green but asymptomatic carrier of 1 blue gene)
It is a Dominant gene mutation present on autosomes or genes containing DNA. A mutation of Dominant genes is preferably referred to as a Factor rather than a mutation which is typically recessive. Here we always observe a form of dominance over the Wild Type and this depending on whether it is a Dominant-autosomal mutation following one of the 3 distinct dominance modes;
* Dominant (Complete) where there is complete dominance over the Wild-Type. Here the heterozygous and the homozygous are absolutely IDENTICAL. Here is an example of a cross involving a Factor-Dominant:
Wild-Type X dfDominant (doublefactorDominant):
100% sfDominant (singlefactorDominant) visual mutant
or with a known Factor (mutation)
Green X dfGrey-Green
* Dominant-Incomplete where there is incomplete (partial) dominance over the Wild-Type. Here the heterozygote is visually different and ALWAYS intermediate in coloration between Type-Wild and homozygous (dfDI). Here is an example of a cross involving 1 Factor-DI (Dominant-Incomplete):
Wild-Type X dfDominant-Incomplete:
100% sfDominant-Incomplet (Always intermediate between the Wild Type (or other mutation at the base of the cross) and the dfDI)
or with 1 known factor:
Green X dfStrong (Olive):
100% sfFonçé (Vert-Fonçé) (intermediate between TS (Green) and dfDI (Olive)
* Co-Dominant where there is a cooperative phenomenon (hence Co-Dominant) observed only between mutations of a series-multiple-alleles and therefore of the same locus without direct regard to the Wild-Type. In all the loci we find a complete mutation and several incomplete mutations (partial) An example of series-allele-multiple mutations of the same locus:
The blue locus where we find a complete mutation; blue and several blue-incomplete mutations (aka parbleu de bleu-partial) such as aqua and turquoise (separate mutations and not the same!)
Here the mutants are always double-heterozygous (double-carrier or carrier of 1 mutant gene for each of the cross mutations) but always visually intermediate between the 2 cross mutations. Since intermediate, the double-heterozygous mutants then form a composite variety.
It is very important to note and ALWAYS remember that there is on the other hand in co-dominance no homozygote since it is not at the base of a single mutation but of 2 mutations which are crossed. In addition, it is also very important to note and always remember that there is NEVER a phenomenon of dominance / recessivity between the mutations of a series-alleles-multiple but ALWAYS of co-dominance between them.
Here are some examples of crosses involving the phenomenon of co-dominance between mutations of a series-alleles-multiple of the same locus;
mutation1 X mutation2:
100% variety-composite (ALWAYS intermediate between mutations 1 and 2)
or with known allied mutations:
aqua X turquoise: 100% aquaturquoise (intermediate between aqua and turquoise)
aquaturquoise X aqua: 50% aquaturquoise – 50% aqua
aquaturquoise X turquoise: 50% aquaturquoise – 50% turquoise
Stéphane alias Tintin,
Birdhouse Les Yeux de Ruby.
“You are responsible for what you tame forever”
– Antoine de Saint-Exupéry