Basic Ball Python Genetics

Remember back in high school biology when you were studying genetics using pea plants to determine what colors their flowers could be? Did your eyes glaze over? Did you ever think that you would use any type of genetics in your life? Well, now is your opportunity to return to those days and brush the cobwebs out of your mind. Genetics is not the easiest subject, but it is essential to understand the basics as you pursue your quest to produce unique ball pythons.

Before taking a look at the many different color and pattern mutations that are available in the ball python market today, it is important to have a basic understanding of genetics. This knowledge is essential when planning your breeding projects, and will help protect you from sellers who are trying to take advantage of people who do not understand how the various color and pattern mutations, also known as morphs, are produced.

Some of the basic genetic terms are listed here. DNA: Deoxyribonucleic acid. This is the molecule that forms the genetic code.

Chromosome: Most cells in living organisms have a nucleus. Much of the nucleus is made up of paired chromosomes; the number of pairs is constant within a species. Each chromosome is a single, long strand of DNA in a protein matrix.

Gene: The units of DNA that are transmitted from one generation to the next in the sperm and egg cells. Each gene codes for a specific protein. Each protein functions in a specific step in the biochemical pathway that determines an individual's phenotype. There are numerous genes on each chromosome.

Allele: One of two or more alternate forms that a gene may take. A changed, or mutant, allele at one locus can block or divert a biochemical pathway to produce a phenotype that is different from the normal.

Locus (plural = loci): The location on a chromosome where a specific gene resides. Think of it as a street address.

Genotype: The genetic makeup of a plant or animal. The identity of an allele or alleles that a single individual has at one or more specified loci.

Phenotype: The physical characteristics (such as eye color or scale color, but also including physical traits not easily observed, such as innate disease immunity) of the animal as dictated by the genes it has inherited and the influences of its environment.

Heterozygous: Having two different alleles at a given locus. Breeders often shorten this term to "het."

Homozygous: Having two identical alleles at a given locus.

Wild type: The phenotype most commonly seen in wild-caught individuals, usually considered the normal appearance. The allele at each locus that produces the wild-type phenotype.

Recessive: A mutant allele that changes the phenotype only when it occurs in the homozygous form. When heterozygous, the individual looks normal.

Codominant: A mutant allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual does not look like a homozygous individual, and neither does it look like a normal one.

Dominant: An allele that changes the phenotype when either homozygous or heterozygous. A heterozygous individual looks like a homozygous individual.

Double heterozygous: Heterozygous at two gene loci.

Triple heterozygous: Heterozygous at three gene loci.

Punnett square: A learning tool for determining the possible outcomes of a given cross between individuals. It was developed by R.C. Punnett, an early British geneticist.

Symbols

Some of the names used to describe various color and pattern mutations are rather long. For example, the name "lavender albino" contains 14 letters. Using the entire word when filling in a Punnett square would make it enormous. Abbreviations or symbols are used instead of the entire name when describing the mutation. Mendel originated some of the rules used for symbolizing today. The rules are as follows:

1. The symbol is a unique, one- to four-letter abbreviation of the mutant name. For example, a could be used for albino. As a is already taken, ax could be used for axanthic.

2. All characters in a recessive mutant's symbol are lower case. Again, a is for albino, a reces­sive mutation.

3. All characters in a dominant or codominant mutant's symbol are lower case, except for the first letter, which is upper case. For example, Pa could stand for pastel, a codominant mutant in the ball python.

4. The symbol of the locus is the same as the symbol for the first mutant gene found at that locus. For example, a stands for both the albino mutant gene and the albino's locus. Pa stands for both the pastel mutant gene and the pastel's locus.

5. The symbol of the wild-type or normal allele at each locus is the locus symbol followed by a plus sign as a superscript. For example, the wild-type allele at the a locus would be a+. The wild-type allele at the Pa locus would be Pa+. If usage is clear, the wild-type allele can be symbolized by a plus sign alone.

6. As genes come in pairs—one from the father and one from the mother—there are two alleles in a genotype. The two symbols may be separated by two slash marks (//), partic­ularly in complicated genotypes. While useful, the slash marks are optional. For example, an albino individual could be symbolized as either a//a or aa. A heterozygous pastel could be either Pa//Pa+ or PaPa+.

7. The more dominant allele goes on the left side of the genotype, and the more recessive allele goes on the right side of the genotype. For example, a heterozygous albino would be a+a 8.

8. Always remember to clearly label all the symbols used in your Punnett squares.