Medaka Selective Breeding Genetics: Breeding Strategies to Control Body Color, Body Shape, and Fin Morphology
This article explains the fundamentals and applications of genetics required for medaka selective breeding, including concrete breeding strategies and strain management methods.
Key Takeaways
This article explains the fundamentals and applications of genetics required for medaka selective breeding, including concrete breeding strategies and strain management methods.
Medaka selective breeding can be advanced strategically by understanding the laws of inheritance. By switching from intuitive selection to a scientific approach, it's possible to create desired breeds more efficiently and reliably. This article systematically explains the fundamentals of medaka genetics, practical breeding strategies, and strain management methods.
Fundamentals of Medaka Genetics: Mendelian Laws in Practice
Many traits in medaka—such as body color, body shape, and fin morphology—follow Mendelian inheritance. Dominant genes express their traits with just one copy, while recessive genes only manifest when two copies are present.
Consider the blue body color (b gene) as an example. When a blue medaka (bb) is crossed with a wild-type individual (Bb), all F1 offspring are Bb and blue does not appear. However, when F1 individuals are crossed with each other, the F2 generation shows a 25% probability of bb (blue body color). In this way, fixing recessive traits requires selective breeding in the F2 generation and beyond.
Additionally, medaka employ an XY sex determination system, and some color genes are located on the X chromosome. With X-linked genes, males carry only one X chromosome (hemizygous), so recessive genes immediately manifest as phenotypes. Therefore, even with the same genotype, the phenotypic ratio differs between males and females, which must be incorporated into breeding design.
Major Traits and Inheritance Patterns: Body Color, Shape, and Iridescence
Medaka body color is determined by the quantity and distribution of four types of pigment cells: melanophores, xanthophores, leucophores, and iridophores. The major genes involved are:
- b (blue) gene: Reduces melanophores and produces blue to white body colors. Recessive, requiring two copies
- hy (himedaka) gene: Enhances yellow and orange tones. Forms the foundation of the Yougui line
- i (ivory) gene: Lacks xanthophores. The bb × ii combination produces white body color
- rr (reduced scale) gene: Alters the reflective layer of scales (iridophores), involved in the iridescent stripe of the Yamato line