| ORIGINAL BOOK REVIEW by Dr. Rainer R. Erhardt "Well, there is help on the horizon and anyone seriously interested in color genetics should take a look at Linda Rubin's book: COCKATIEL GENETICS MADE EASY! Though this book is primarily directed to breeders of cockatiel mutations, there is enough information in this little volume to teach anyone the secrets of dealing with recessive, sex-linked, and dominant mutations..." ACBM, Vol. 65, No.12 CLICK TO READ THE REST OF THE REVIEW! 112 pages, 15 chapters, glossary & more! |
Copyright 2006 Linda S. Rubin
| Multiple Bird Households by Linda S. Rubin |
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| The Genetics of Bald Spots in Lutinos and a Discussion of Selective Breeding Copyright © 2005 LINDA S. RUBIN CF Genetics Consultant/Panel Judge All Rights Reserved www.CockatielsPlusParrots.com Selected Q&A's "From My Mailbox" Q. Some Lutino cockatiels show a bald spot. Can one tell something about genetic interrelation? Is baldness dominant or recessive? Best regards, Joanna A. Your question is most astute and provides an opportunity to discuss genetics away from the context of color mutations. Genetic modes of inheritance not only influence color mutations but they also control all the genetic traits found in a cockatiel, or the cockatiel genome. Consider this short overview. Genes determine all of a cockatiel’s hereditary characteristics and are carried on its chromosomes. Chromosomes are found in the cell nucleus and are composed of a set of threadlike structures made up of DNA and a protein. The point to remember is that chromosomes always travel in pairs. This is why we always chart our color expectations in each parent as pairs whenever we attempt to predict the color of future offspring based on the parents’ genes. For example, sex chromosomes are written as XX and XY, representing the cock and the hen, respectively. We then add any sex-linked color mutation genes that we know each parent carries on their “X” sex chromosomes (unfortunately, the hen’s Y sex-chromosome is too small to carry color genes). Similarly, the autosomes - the remaining chromosomes that exclude each parent’s pair of sex-linked chromosomes - are also written in pairs. For example, an (autosomal recessive) Whiteface mutation and an (autosomal co-dominant) Dominant Yellowcheek mutation pairing would be written as: ww and YY, respectively. Consider, however, that we are not merely confined to just color mutations because any trait that is able to be inherited can be substituted in our charting, once we discover it’s working mode of inheritance – whether it be sex-linked recessive, autosomal recessive, co- dominant, etc. (Albeit, this is a very simplistic explanation because many genes do, in fact, work in conjunction together). However, simply stated, chromosomes carry genes for both good and bad traits, genetic strengths and weaknesses, and yes, show attributes and show faults. In short, genes come in both desirable and undesirable traits including deadly lethal factors – whether visible to our eye or hidden below the surface. Although the trait for baldness in cockatiels does not quite qualify as a true lethal factor, it is considered to be a very undesirable trait. Nearly any undesirable trait can be bred out of cockatiel breeding stock when using a responsible, planned genetic program such as selective breeding that spans several generations. You are indeed correct in that the undesirable genetic trait of baldness is inherited, although it is unproven under which mode of inheritance it operates. However, most faults that disappear and tend to resurface during subsequent generations are assumed to be recessive. Like many faults, the inherited gene for baldness may remain in a line as an autosomal recessive until it matches up with another cockatiel that is either carrying or expressing the identical trait for baldness. The resulting progeny of pairing even “split” partners would include a percentage of young that show the bald spot visually, as well as a percentage of young that carry the trait for baldness as heterozygotes (splits). What we do know is that, over time, through carefully planned, selective breeding programs it is possible to completely eradicate undesirable traits such as baldness; however, this does not imply that it is easy. This principle applies to any trait you may wish to eliminate, be it poor parenting skills, inherited tendencies to feather pluck, undesirable personality, poor parenting skills (e.g., lack of interest to incubate eggs full term and/or feed out young through weaning), show faults, mutation faults including baldness, or any other undesirable trait to be eliminated. This method has been used successfully by livestock breeders for countless generations and when strictly adhered to will work for any breeding stud. The skill lies with the aviculturist and the program that he or she chooses to employ. By selective breeding and rigorously culling (selling as pets) any offspring that show the slightest tendency for baldness, you will take control of your breeding program. Now, chicks are “selected for” desirable traits (e.g., well-feathered heads lacking any outward sign of a bald spot). This may actually prove to be a long process because a breeder cannot expect to produce offspring in the first generation, all of which lack a bald spot, when produced from at least one bald parent or from adults that may carry a recessive gene for baldness in hidden form. It may take several generations, at minimum, to selectively breed out the bald spot by pairing these adults to more desirable partners; in other words, by repairing balding birds to other cockatiels that do not carry the same fault visually or in previous generations. There are some short cuts to take to eradicate the bald spot and care must be taken not to outcross or breed back any birds that may reintroduce the trait for baldness back into the line. For further comments about bald spots, please refer to my article Breeding Lutinos and Whiteface Lutinos. To learn more about selective breeding to eradicate show faults, see: Rewarding Genes on the Show bench and “Linebreeding and Inbreeding Practices,” which explains these concepts in greater detail. |
| The Genetics of Bald Spots in Lutinos & a Discussion of Selective Breeding Copyright © 2005 Linda S. Rubin All Rights Reserved |