4.1 Genetic Notation

Chapter 4: Multiple Mutations

So far we have discussed outcomes of pairs carrying only one mutation. Ino or blue or spangle. In this chapter we will learn how we can predict outcomes of pairings where one or both birds are carrying more than one mutation. 

4.1 Genetic Notation
We have used very simple notation to represent dominant and recessive genes. We used G to represent a green (normal) gene and B for a blue gene. This is not standard genetic notation and presents a very simplified view. We will now look at the placement of genes on the DNA to introduce the standard genetic notation.

We have defined the gene as a section of the DNA which deals with a specific feature of the bird. A change in any gene which makes it different from the normal is called a mutation. Imagine that the DNA looks something like figure 4.1 

The DNA has a long chain like structure with two copies of each gene. The different shapes shown represent different genes. Let us say that the circle represents the place where the blue gene may be located on the DNA. This place is called the locus of the blue gene. Similarly, lets us say the star represents the place where the spangle gene may be located and this location is known as the locus of the spangle gene. 

Each mutation has a standard symbol for the mutant gene. For example the blue gene is represented by the letters bl. A bird with two blue genes will be represented by bl/bl. (see http://www.euronet.nl/users/hnl/symbols.htm for a full list of standard gene symbols) 

It is very important to note here that even if the blue gene is not present in a bird, the locus of the gene is still there and is occupied by the normal gene. We represent the normal gene present at the locus of the blue gene by bl+. A bird with no blue gene is written as bl+/bl+. A bird with one blue gene and one normal gene is represented by bl+/bl. See fig 4.2


Let us now revisit the Green X Blue pairing and use standard notation to make a Punnett square.

We get 100% bl+/bl which is normal split to blue. 

Try the following pairings using standard genetic notation and give your answer as symbols with description.
A) Blue X Green Split blue
B) Green Split blue X Green Split blue


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