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Betta Genetics

Betta genetics can be very complicated or very simple depending on what we look at. Before I attempt to explain any genetics however there are a few general (very oversimplified) laws of heredity you should know (for those somewhat familiar with genetics, skip ahead of all this mumbo jumbo).

To begin with, for each characteristics every organism inherits two genes, one from their dam and one from their sire. Bettas are made up of millions of these gene pairs. An organism's genetic make-up is called it's genotype. Basically, these gene pairs are what determine an organisms physical appearance. The physical appearance of an organism is referred to as it's phenotype.

Each characteristic generally has a recessive and dominate form of a gene. When there are two different forms of a gene the forms are called alleles (i.e.: the dominant allele and the recessive allele). If an allele, in a pair of genes, is dominant, the dominant copy overrides a recessive copy. The only way a recessive gene is expressed is if there are two copies of it. An organism with two same copies of a gene (either dominant,dominant or recessive, recessive) is referred to as homozygous. When two homozygous organisms are crossed their offspring are all homozygous for that trait. An organism with two different copies of a gene (dominant, recessive) is call heterozygous. When two heterozygous organisms are crossed half of their offspring is heterozygous and half is homozygous. Confused yet? Don't worry - you will catch on!

Lets begin with a simple dominant/recessive gene - the gene that make a Betta either a single tail or a double tail. In Bettas, a single tail is dominant to a double tail.

This is a double tail Betta - notice the tail is split into two lobes. His alleles are dt,DT
This is a single tail Betta - his tail is only one lobe. His alleles could be S,S or S,DT

Photos provided by Liz-Hanh Morin

 
Relationships between genotype and phenotype
Alleles
DT + DT
S + DT
S + S
Genotype
Homozygous
Heterozygous
Homozygous
Phenotype
Double tail
Single tail
Single tail

When we cross two Bettas their offspring's phenotype depends on the alleles present in the parents' genotype. If we cross two double tail Bettas we know that they are both homozygous and therefore all of their offspring will be double tails too. We can use a table to demonstrate how this works. Middle, right hand squares represent 25% of a spawn.

 
 
DT
DT
DT
DT,DT
DT,DT
DT
DT,DT
DT,DT
Alleles 100% DT,DT
Genotypes 100% Homozygous
Phenotypes 100% Double tail

Now what happens if we cross two homozygous, single tail Bettas? All of their offspring will be homozygous single tails.

 
S
S
S
S,S
S,S
S
S,S
S,S
Alleles 100% S,S
Genotypes 100% Homozygous
Phenotypes 100% Single tail

Allrighty, now that you're an expert, let's try something a little bit trickier. Let's cross a double tail to a homozygous single tail. Come on, quit sweating! Just examine the table below. Remember, the single tail is dominant to the double tail and one single tail S will override a double tail DT.

 
S
S
DT
S,DT
S,DT
DT
S,DT
S,DT
Alleles 100% S,DT
Genotypes 100% Heterozygous
Phenotypes 100% Single tail

See now that wasn't too bad was it? Ok, now for the real quiz! What will you get if you cross a heterozygous single tail to another heterozygous single tail?

 
S
DT
S
S,S
S,DT
DT
S,DT
DT,DT
Alleles 25% S,S, 25%DT,DT, 50% S,DT
Genotypes 50% Homozygous, 50% Heterozygous
Phenotypes

 

You figure it out!

What percent are single tails and What percent are double tails?

Click here to see if you're correct.

 

 

Additional Genetics Pages

 

Ok, last question. What happens if you cross a heterozygous single tail to a double tail? What about a heterozygous single tail to a homozygous single tail? Fill out the form below and I'll tell you if you are right.

NOTICE:

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Tail Genetics Quiz

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Heterozygous Single tail x Double tail

Alleles:

Genotype:

Phenotype:




Heterozygous single tail x Homozygous single tail

Alleles:

Genotype:

Phenotype:



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