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Monohybrid Inheritance

This is the basic of Mandelian Genetics. Bettas, like most other organisms, are diploid, i.e. they have 2 sets of chromosomes per cell. During the production of gametes (sperm and ova), the cells divide via meiosis and end up with only one set of chromosomes each, i.e. they become haploid cells.

Therefore, let's just start with an easy one - take into consideration just one monohybrid factor. For example, a double-tail fish would have 2 sets of the double-tail allele, dt (It's written in small letters to show that it is a recessive allele). As a result, the gametes from a double-tail betta would have one dt allele per cell. In this example, let's just breed a dt dt (double tail) to a dt dt:

Parental phenotype	Double-tail		x		Double-tail
Parental genotype	dt dt		x		dt dt
Parents' gametes	dt	dt		dt		dt
F1 genotype	dt dt		dt dt	dt dt	dt dt
F1 phenotype	All double-tails (dt dt)

•  The "x" denotes "crossed with".

• Note that the term "F1" can only be used to represent the "first filial generation", and if 2 of these F1 fish were to be crossed their offspring will be called F2.

• To get the F1 genotype from the parents' gametes, just do a permutation of all possible combinations of the gametes. For example, if the father's gametes are A and B, and the mother's gametes are C and D, then possible combinations would be AC, AD, BC and BD. The only possible combinations are those where the father's gametes fuse with those of the mother's, so AB and CD are not possible.

• An easier method to do it is to use a Punnett Square, as shown below:

OK, it doesn't look exactly like a square but you get the idea. =)

Now that you've got the hang of it (I hope!), let's work on another example.

Father: Double-tail (dt dt)
Mother: Single-tail (DT DT)

So here you get all of your F1 offspring having the DT dt genotype (it's conventional to write the dominant allele in front of the recessive allele when both are present together), so all of them will turn out to be single-tail fish with double-tail geno, or simply single-tails that are heterozygous for double-tail.

Now let's try crossing 2 of these F1 generation and see what we get:

Tah-dah! Your F2 generation will show 75% single-tails and 25% double-tailed fish. 25% of the spawn will be homozygous for single-tail (DT DT) while the other 50% will be single-tailed but heterozygous for double-tail, just like their parents.

OK, now that you're familiar with the classical 3:1 ratio of the F1 x F1, let's get on to the part where modification of the classical 3:1 ratio. There are several reason for this, including :

1. Incomplete Dominance (F2 ratio is 1:2:1)

2. Codominance (F2 ratio is 1:2:1)

3. Lethal genes

4. Multiple alleles

5. Linked Genes

I'm muuuucch too lazy to go through all of them, so let's just get to those important for bettas instead, haha!

1. Incomplete Dominance

This phenomenon is most popularly characterised by the blue colouration in bettas. The blues family comprise of 3 main blue colours: royal blue, turquoise and steel blue. Let "Bl" represent the dominant allele coding for the blue colour, and "bl" represent the recessive allele coding for blue colouration.

For a start, Bl Bl gives turquoise fish, bl bl gives steel blue fish and the heterozygote Bl bl gives royal blue.

So, we're done! Let's try this cross:

Father: Turquoise (Bl Bl)
Mother: Steel blue (bl bl)

So all the F1 fish will be Royal blues! (Bl bl)

Now to make sure you're done with this lets get the F1 x F1 done:

F1 father: Royal Blue (Bl bl)
F1 mother: Royal Blue (Bl bl)

So in the F2 spawn you get 25% turquoise (Bl Bl), 50% royal blues (Bl bl) and 25% steel blues (bl bl). OK, so we're done!

2. Codominance

Codominance occurs when a pair of alleles results in the production of 2 distinct and detectable gene products. Therefore, in heterozygotes, gene products of both alleles are expressed, and the phenotype has the characteristics of both parents.

An easy example would be a cross of a blue fish with a red one. The resulting offspring will have both blue and red colours, since these 2 alleles express themselves as strongly as one another. The genetic diagram would have to involve dihybrid inheritance, so I'll just leave it as it is here and maybe go into it in the "Dihybrid Inheritance" section. OK, fine excuse for being lazy, heheh.

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OK, too tired to go on now, maybe I'll update this page again soon .... tune in again, yeah?

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