Question: I paired a Yellow Lacewing together with a Grey Green hen and got an Albino. I have checked this bird out every week for the last two months but have not found a cinnamon spot or mark or tail quill anywhere. Is this answerable?
Answer : In one word Kerry, Yes, but I am afraid the answer is rather lengthy.
The variety of budgerigar known as the Lacewing has recently been proven to be a composite variety of both Cinnamon and Ino: In other words the Lacewing is in fact a Cinnamon-Ino and there is no such entity as a Lacewing gene (although some breeders think so).
The Lacewing variety is produced as a result of the closeness of the Cinnamon and Ino alleles (genes) on the same chromosome: and is known as linkage, but this term should not be confused with the term "sex-linkage" (although both Cinnamon and Ino genes are in fact sex-linked!). The loci (position on the chromosome) of the alleles for Cinnamon, Ino and Opaline are all found on the X chromosome and as a result of their pattern of inheritance, these three varieties are described as sex-linked. (I have discussed a sex-linked variety in Question 2, and if you need further understanding of the phenomenon of sex-linkage, then I suggest that you read that question first.)
During the process of cell division in the formation of gametes (eggs and sperm cells) known as meiosis, the pairs of chromosome come together at points along their length known as chiasmata, and at these points of "crossing-over", the chromosomes exchange DNA material so that the gametes contain lengths of DNA from both parents. Chiasmata, can occur at many different points along the length of the chromosomes, and if two different alleles are close to each other along the length of the chromosome, then the incidence of crossing-over occurring between the loci of the two alleles will be much less than if the loci of the same alleles were at some distance to each other on the chromosome.
If one studies the effects of two different genes together, most genes behave as though they operate totally independently of each other. However, in the budgerigar, there are three pairs of genes which show the close relationship of the pairs of genes to each other:
In the case of the Lacewing, until the Cinnamon and Ino alleles are located on the same chromosome, then the Cinnamon and Ino genes will operate absolutely independently of each other. However, once the "cross-over" has taken place, the Cinnamon and Ino genes appear to act as a single Lacewing gene, because chiasmata only occur between the two alleles, infrequently -see Diagram 1.
When the Cinnamon and Ino genes are on the same X chromosome, this is referred to as Type I Cinnamon-Ino (Lacewing), whereas, when the Cinnamon and Ino genes are on different X chromosomes, this is referred to as Type II Cinnamon-Ino (non-Lacewing). The occurrence of chiasmata between the Cinnamon and Ino genes acts as a two-way process (although in reality it is just a single process) whereby, crossing-over links the Cinnamon and Ino alleles to produce the Lacewing phenomenon, and also the same frequency of chiasmata occurring between the Cinnamon and Ino alleles on a "lacewing chromosome" will produce the "reverse cross-over" or unlinking, of the two genes so that the Cinnamon and Ino genes are again located on two separateX chromosomes and therefore act independently of each other: -see Diagram 2.
During the crossing -over phase of meiosis, both chromosomes in each pair of autosomes (non-sex chromosomes) are of equal length, both before crossing over and after the process, whereas, in the case of the sex chromosomes, only a pair of X chromosomes (which are always of the same length) can actually complete the crossing-over, so this can only occur in the cock during spermatogenesis, because only the cock has a pair of X chromosomes. In the case of the hen, the sex chromosome pair consist one X chromosome and one Y chromosome, and since the Y chromosome is a "dummy chromosome" (thought to contain no useful genetic information in the process of heredity), no material is exchanged between the X and Y chromosome during oogenesis (the meiotic production of egg cells). Therefore sex-linked cross-overs (and reverse cross-overs) of Cinnamon-Opalines and Cinnamon-Inos (Lacewings) is a phenomenon occurring in the male bird only. The splitting of a cross-over link from a Lacewing Type I , X chromosome cannot occur in a phenotypic Lacewing cock because both X chromosomes are the same Type I , and thus different genetic material cannot be exchanged. Therefore, the reverse cross-over can only occur in a a male bird split for Lacewing: i.e., Normal/Lacewing or Cinnamon/Lacewing or Ino/Lacewing
In the case of the autosomal cross-over linkage between the Dark and Green/Blue genes, the phenomenon will occur equally during meiosis both in spermatogenesis and oogenesis, in the testes and ovaries, respectively. The frequency of crossing-over, to produce the Lacewing phenomenon and the reverse process, to separate the linkage of Cinnamon and Ino genes, has been calculated to occur about once in every 36 offspring produced (3% occurrence), which indicates that the Cinnamon and Ino alleles are very close together.
Now, with specific regard to your question, because of the fact that multiple genes are in action here, I will examine each gene system separately. The Yellow Lacewing cock is in fact a Green series bird and when mated to a Grey-Green hen, a Blue series bird (Albino) has been produced. For this to occur, both the cock and hen must be Bb heterozygous Green/Blue. eg. Bb x Bb produces 25% BB (Green) 50% Bb (Green/Blue) 25% bb (Blue).
For the Cock to have a Lacewing phenotype, he must be homozygous for both Cinnamon and Ino (have Cinnamon and Ino genes on both X chromosomes - both Type I chromosomes) Xci Xci, and since the Grey-Green hen is a Normal XY, she carries neither Cinnamon nor Ino gene (remember, she has only one X chromosome and if any of the sex-linked genes were present, she would display that phenotype).
The Albino offspring could only inherit the Ino gene from the cock, therefore, the Albino offspring must be a hen. However, since the cock is homozygous for both Cinnamon and Ino, one would expect that any of his X chromosomes inherited by his offspring would possess both Cinnamon and Ino genes on a Type 1 chromosome, thus producing 50% Lacewing daughters and 50% Normal /Lacewing sons: eg. Xci Xci x XY produces 50% Xci X Normal /Type I Lacewing cocks 50% Xci Y Lacewing hens.
You are still waiting for some cinnamon markings, which may eventually appear (Lacewing markings develop with maturity of the bird), thus confirming that the Cinnamon gene has also been inherited, and at present, this budgerigar may be a poorly marked Lacewing. When this bird is mature enough to mate, if you wish to check the true genetic identity of this Albino (?) youngster, then mate her with a Cinnamon cock, and if she is a Lacewing, she will produce all Cinnamon offspring, and the production of Cinnamon cocks will prove that the hen possesses the Cinnamon gene: eg. Xc Xc x Xci Y (suspect hen) produces 50% Xc Xci Cinnamon / Ino cocks 50% Xc Y Cinnamon hens. Once you have test-mated the Albino (?) hen in question, and conclusively proven that she does not possess the Cinnamon gene, then there are several reasons why the production of an Albino offspring, from the mating of a Lacewing cock to a Normal hen, appears to confound genetic theory.
As I have mentioned in other answers, there is a mutational rate for every individual allele, and as the budgerigar hobby has seen over the past century, there have been at least 28 different colour mutations identified in the budgerigar: for reasons explained (final paragraph of Question 16). There are probably many, as yet unidentified, recessive gene mutations in existence in the captive budgerigar gene pool which will only appear as phenotypes with close in-breeding.
If your Yellow Lacewing cock has failed to pass on either of his two Cinnamon genes to a confirmed Albino daughter, then, for one reason or another, during meiosis, one of the Cinnamon genes has either reverse-mutated (reverted) to a Normal allele (remember Cinnamon is a mutation of a Normal "wild-type" gene) or the Cinnamon gene allele has been lost or damaged during the process of meiosis.
If you are interested in the technicalities of genetics on a cellular level, then there are plenty of genetics textbooks, which will explain such details at great length. I would be most interested to learn of the outcome of any test matings that you carry out with your Albino (?), please keep me posted.
Editors' note: I regret that Dr Pilkington is unable to answer any further questions.
Original text Copyright © 1998, Dr John Pilkington
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