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This page will go over the scientific biological aspects of Chao. Please be warned that section goes into complicated details, and is intended for advanced Chao breeders only!

Genetics of Chao is the study of Chao genes and heredity when breeding. The genetics of Chao vary across the games they appear in, and the nature of Sonic Adventure and Sonic Adventure 2 genetics still have much mystery behind them. In later release, the genetics and heredity of Chao are known to bear much similarity to the genetics of real world organisms, with many traits determined by a Chao's genes. The major areas of genetics are Appearance, Stats, and Personality.

Sonic Adventure

When breeding two Chao, whether it is done in the Garden or within the VMU has a substantial effect on the resulting child Chao. When performed in the garden, the resulting baby will be essentially like any other newly born Chao- there are no notable effects of heredity. But when breeding within the VMU, a child Chao will hatch with traits taken from both parents.

The baby will start with stats at about 10% of the parents' averaged together, and with around 50% of their averaged HP. The exact inheritance values are still unknown. Additionally, VMU breeding allows for new breeds of Chao when breeding special Chao- the specially obtained Gold, Silver, and Black Chao. Unlike the post-DC era of Chao, breeding in SA1 allows for mixing of colors, to some degree, to obtain new kinds of Chao.

When breeding a Normal Chao and a Gold, Silver, or Black Chao the resulting child has a 50/50 chance of being Normal or the special breed parent. When breeding special breed parents, either a Gold or Silver with a Black Chao, the resulting child may be Normal, either of the parents' breed, or a new mixed breed. The chance of obtaining a new breed is roughly 1/10. For example, when breeding a Gold and Black Chao the child may be Normal, Gold, Black, or a new darker-gold Chao, known as a Copper Chao. Similarly, breeding a Black and Silver Chao can produce an Onyx Chao, which appears as a darker-silver color. There are also reports that breeding a Silver and Gold Chao can produce a new breed, called a Bronze Chao, however this has yet to be documented.

The exact nature of the genome of SA1 Chao is unknown, and more tests are required to make conclusive statements. For example, it is unknown if a child Chao carries the genes of its parents- will a Normal Chao produced from breeding a Silver and Gold Chao still have Gold and/or Silver genes? It is also unknown if chao are haploid or diploid- that is, if chao have two alleles for appearance, and the interplay of Gold/Silver and Black produces the Copper/Onyx chao, or if Jewel and Color are separate genes, but the Chao only have one allele for each category. Similarly, the exact way breeding a Gold and Silver Chao can produce a Normal Chao is a mystery.

Sonic Adventure 2

Breeding Chao in Sonic Adventure 2 behaves in a similar way to SA, where VMU breeding will allow for special breeds of Chao. This game had the same Black, Silver, and Gold chao of Sonic Adventure, and the online Black Market introduced several other new breeds: Ruby, Sapphire, Amethyst, Emerald, and Moon Chao. The online Black Market is now down, which has caused much greater difficulty in obtaining these new Jewel Chao types, and testing the genetics of Sonic Adventure 2. There are rumors that the Jewel Chao could be bred to produce other new types of Jewel Chao, such as Aquamarine Chao, in addition to the Onyx and Copper Chao types from Sonic Adventure. The genetics, and even breeds, of Chao in both Dreamcast games have much remaining mystery.

Sonic Adventure DX and Sonic Adventure 2 Battle

In games after the Dreamcast era, Chao, like real organisms, have both a phenotype and genotype. The phenotype is the observable characteristics of the individual Chao, and the genotype is the full genetic information of the individual Chao, which determines phenotype and may carry unseen characteristics that could be transferred to a Chao's offspring.

The Chao genome, the total set of variable genes present within a Chao, has the major genetic categories of appearance, stat grades, and personality. Appearance genes are those for Colour, Tone, Shininess, and Jewel Coat. The stat grade genes include each stat (both visible and hidden), Swim, Fly, Run, Power, Stamina, Luck, and Intelligence. The only known personality gene is that which determines a Chao's favorite fruit. However, the details of genes which may effect personality are an area of ongoing research; there could likely be more personality related genes.

Chao are diploid organisms, meaning they carry two alleles for each gene. Alleles are the possible forms of a gene, and these alleles determine the phenotype of a Chao, based on rules of gene dominance. A Chao may have two different alleles for a given gene, making the Chao "impure" (or heterozygous) for that trait, in which case its display of the gene will be determined by the dominance of one gene or another. A Chao may also have two of the same allele, making the Chao "pure" (or homozygous) for that trait. Chao which start off in the garden, or those which are purchased from the Black Market or Tiny Chao Garden Market are pure in all genes. These Chao are easier to track the genetics of for breeding purposes than those with many impure sets of genes.

Appearance Genes

The genes for appearance are separated into Colour, Tone, Shininess, and Jewel Coat. When breeding Chao, these four genes are all independent of each other, and are often additive in appearance. However, there are occasions where the appearance of a Chao is not additive, and the resulting interplay of genes will cause unexpected appearances, such as Shiny Jewel Chao or Bright Chao.

Colour has 14 possible alleles, which are Normal, White, Red, Blue, Yellow, Pink, Purple, Sky Blue, Orange, Green, Brown, Grey, Lime Green, and Black. All colours except Normal have equal dominance. If a Chao has Red and Blue colour alleles, it will have an equal (50/50) chance of being red or blue when born. The Normal colour gene is recessive compared to all other colour genes. If a Chao has a Normal allele and a different coloured allele, the Chao will display the second colour, not the Normal colour. To have a Normal colour phenotype, a Chao must have two Normal colour alleles.

Tone has 2 possible alleles, which are Mono-tone and Two-tone. These two alleles are equally dominant, so if a Chao has a mono-tone and a two-tone allele, it will have an equal (50/50) chance of being mono-tone or two-tone.

Shininess has 2 possible alleles, shiny and non-shiny. These two alleles are equally dominant, so if a Chao has a shiny and a non-shiny allele, it will have an equal (50/50) chance of being shiny or non-shiny.

Jewel Coat has 12 possible alleles, which are Non-Jewel, Silver, Gold, Ruby, Sapphire, Amethyst, Emerald, Garnet, Aquamarine, Peridot, Topaz, and Onyx. All Jewel Coats except for Non-Jewel have equal dominance. If a Chao has a Sapphire and a Ruby allele, it will have an equal (50/50) chance of being Sapphire or Ruby. The Non-Jewel coat gene is recessive compared to all other coat genes. If a Chao has a Non-Jewel allele and any jewel coat allele, the Chao will display the jewel coat. A jewel coat will visually override all tone or colour traits. If a Chao has any jewel coat, it will not display its color or tone. All Chao purchased from the TCG Market have two Normal Colour alleles and two Two-tone alleles hidden under their Jewel Coat. When Jewel Coats are mixed with a displayed Shiny gene, rather strange Chao can result known as Shiny Jewel Chao, which vary in appearance across the games they appear in.

The results of breeding Chao, while knowing the parents' genotypes, can be predicted using a Punnett square diagram. Each diagram describes a "monohybrid cross," or the probabilities for one particular gene being carried to a child. To determine the probability of getting several desired traits across genes, multiple squares may be used, and the resulting probabilities multiplied together.

For example: breeding a Chao with Red/Normal colour genes and Two-tone/Mono-tone tone genes with a pure Two-tone Normal Chao. Since Chao have random dominance (when dealing with equally dominant alleles,) a slightly different notation from standard Punnett squares can be more helpful. Normally a Punnett square uses the same letters, a capital letter for the dominant trait and a lowercase letter for the recessive trait. For Chao it is helpful for alleles to not be represented by the same letter, and have first letter in the square be the displayed trait. Keeping in mind the rules of dominance, it would therefore follow that Normal will always be the second letter, if another is available to be the displayed trait. When two traits are equally dominant, they are alternated which allele is in the displayed "slot" of the square.

For Colour, N represents a Normal allele, and R represents a Red allele. For Tone, T represents a Two-tone allele, and M represents a Mono-tone allele.


The method of randomly choosing a phenotype from two equally dominant alleles is unique to Chao, and not present in real life organisms. Normally when two alleles do not completely express over each other, a third phenotype is produced, in two different phenomenon know as incomplete dominance and co-dominance. Incomplete dominance occurs when having only one allele will cause the organism to produce a less pronounced phenotype- Red+White will produce Pink. Co-dominance occurs when both alleles will display their traits- Red+White will produce an offspring with Red and White portions. Chao do not allow for any color mixing.

Stat Grades

Like appearance genes, stat genes have two alleles each. These alleles represent each possible grade for a stat, E, D, C, B, A, and S. These alleles are all equally dominant, and display the same equal chance determination that equally dominant appearance traits have. Each stat has its own gene set, and the displayed stats (Swim, Fly, Run, Power, and Stamina) may have genes be changed over the course of a Chao's life (or lives.) The displayed trait may be raised through Evolution, causing a permanent change to phenotype and to one allele. The non-displayed stat allele will remain constant through the Chao's life.

For example, a Chao which has B and D alleles for its swim grade, and has a phenotype of a B grade. If this Chao were to evolve into a Swim Chao, its phenotype will now be A grade, and its alleles will be A and D. The D grade allele will always be in the Chao's genotype, while the displayed allele can be raised through repeated evolutions. If the displayed and hidden grade alleles were switched in this case evolution will cause the Chao to have C and B alleles for its swim grade.


The genetics of personality features in Chao is an area of ongoing research. The only known genetic personality trait is determining a Chao's favorite fruit, in which all fruit preferences are equally dominant. Some other personality aspects of a Chao could be genetically determined. A Chao's facial expression is known to be random, not genetically determined, while personality of the Chao is unknown. This is large area of unsolved and unknown features of Chao genetics.