4.2 Alleles


Alleles
Sometimes nature produces two three or even more variants (versions) of the same gene. These variants are called alleles. I will try to explain by a diagram..




We already know that in the DNA two copies of genes are present which may be the same or different. We therefore have two places where the blue or one of its variants may be present. We discussed the possibilities in the budgerigars of the two genes being bl/bl, bl+/bl or bl+/bl+. Things are a little more complicated as more than one type of the blue gene exists. These are called the Blue white face (same as simple blue), blue Yellow face type I, blue yellow face type II and the blue Golden face. All these genes are called alleles of the blue locus. The important thing to understand in this figure is that all these genes can only fit on the DNA in the place represented by the circle. Since there are only two circles on the DNA diagram, only two genes from the list of alleles given on the right can be present in any given bird. There is an order of dominance amongst these genes. The blue white face (bl) being the most recessive or the least dominant and the normal (bl+) or the green being the most dominant. If the two copies are the same, the bird will be a visual of that gene. For example if both copies are blue whiteface then the bird is a visual whiteface blue, if both are blue golden face then the bird is a visual blue golden face. If however the genes are different the bird will be a visual of the gene appearing higher in this list and a split to the other. As an example consider that a bird has a blue Golden face gene and another blue yellow face I gene. The bird will then be a visual blue golden face and split to blue yellow face as blue golden face is higher on the list.

To summarize alleles are different versions of the same gene. Only a maximum of two versions may be present in any given bird. 

Homework
-------------
Which of the following budgerigars is genetically not possible.
1) A Yellowface type I split to whiteface
2) A Yellowface type II split to golden face
3) A Whiteface blue split to golden face
4) A normal split to yellowface II

Comments

Post a Comment

Popular posts from this blog

Record Keeping for Bird Keepers

Image
Bird keeping can be more rewarding with record keeping. Record keeping for bird keepers is maintaining information about each bird, each pair, each clutch & each egg. Furthermore it's about recording your actions related to bird set up, diet, medication etc and the results they produce. Getting Started A few things that you need to get started The first thing you need is the ability to uniquely identify each bird. You must be able to identify every bird listed in your records. If you have only a few birds and their physical appearance makes it straight forward to identify them then you need not worry about this. However, if you have dozens of birds that closely resemble each other you may need a way to positively identify each bird. This process is made easy through the use of leg bands or microchips. A leg band assigns a unique number to a bird which can be used to identify that bird. Microchips may also be embedded in larger species which can be read by an electroni
Read more

Getting Started with Breeding Ringnecks

Image
First of all you need to pick the right cage. Ringnecks require a minimum cage size of 24in x 24in x 48in. The front of the cage should be 24x24 with feeding stations. The depth should be 48inches with the nest box installed outside at the back of the cage. There should be a perch about 1.5-2in in diameter 6-8in from the back wall and just below the opening to the nest box. The logic behind such a setup is that the nest box should be farthest from human approach during feeding times. Birds feels secure in such an environment and are more likely to breed. The illustration below shows this setup. The mesh used for the cage should be rectangular weld mesh and not expanded metal mesh as shown in the picture. The nest box should be filled with white pine shavings 3in deep. The cage should be protected from direct wind and prolonged exposure to sun. While sunlight is great for birds, a shaded area in the cage should always be available to them. Once you have the setup in place, you
Read more

Breeding Alexandrine Mutations: The Lutino

Introduction The Alexandrine is a beautiful bird similar in appearance to the Indian Ringneck. The characteristics that distinguish an alexandrine from an Indian Ringneck include red-brown shoulder patches, a wider neck ring and larger size. While the Indian Ringneck is available in several color mutations the Alexandrine is generally available only in the normal green. It is possible to produce Alexandrine  colour  mutations by hybridizing the Alexandrine with the Indian Ringneck. Such a program however requires a long term commitment, space and responsible breeding practices to be successful and to preserve the purity of both species. In this article a breeding program is outlined that breeds a sex-linked mutation such as Lutino into the Alexandrines. To start the breeding program you need a good normal Alexandrine and a Lutino Ringneck. There are two options at the start of the program. 1) A Lutino Ringneck cock paired to a normal Alexandrine hen 2) Normal Alexandrine c
Read more