2. You\'re a beta fish breeder and have noticed that you have a few fish that di

Question

2. You're a beta fish breeder and have noticed that you have a few fish that display a totally novel ruby red coloring pattern. This ruby red color has since become is very popular in your Etsy store, but you are STRUGGLING to develop a purebreeding strain. Like, every time two ruby red betas are crossed, you end up with a fair number of ruby reds, but still a significant number of betas featuring the standard-type coloration. In your most recent ruby red x ruby red mating attempt, you ended up with 57 ruby red betas and 28 standard betas. All other such matings gave similar phenotypic offspring ratios. Explain what's going on here. (s4 sentences)

Explanation / Answer

1. The color variation in the betta fish is due to the four types of cells, located in layers within the skin. (iridiscent (top) layer, black layer, red layer, yellow (bottom) layer. The red layer contains red cells (erythrophores) which may contain either of these traits, which determine the amount of red in betta fish:

- Normal Red (whole body and fins colored Red, R gene controls the distribution and amount of red; RR betta has more red distribution that rr betta which has reduced red distribution)

- The extended red gene or Er mutant gene is dominant over the normal red color and is so called because the normal red pigment is increased in intensity and distribution.

- Reduced Red (Main body is dark blue or green colour, and only fins are red; no genes have been identified)

- Non-Red (Total absence of red, double recessive nrnr shows no color pigment)
- Variegated Fins (The butterfly effect)

2. The red-loss trait in betta fish will lead to loss of red color in young fishes as they mature. The red loss trait is determined by a distinct gene L, which is variable in expression and dominant over all the red genes, except for Er or extended red.

3. 1st possibility: Since the ruby red X ruby red mating leads to 57 ruby red and 28 standard offsprings. Let us consider, the ruby red parental genotype is Rnr.

male

female

So the genotypic ratio of the offsprings is RR:Rnr: nrnr =1:2:1

So ideally in the total 85 offsprings formed, the ruby red: standard ratio would have been 64: 21. The actual ratio therefore turned out to be close to the predicted one, i.e. 57: 28. So each time a ruby red mating was done, an Rnr parental genotypes were chosen.

4. Second possibility: Suppose the ruby red genotype is ErR in parents, which also has the dominat red loss allele L.

male

female

So all the fishes will turn out to be red when young because despite the genotypic ratio ErEr: ErR: RR = 1:2:1, the phenotypic ratio is ruby red: standard= 4:0

But again the red loss gene is present in every genotype shown above, but will get expressed only in the fishes with RR genotype as L is not dominant over Er. So again the phenotypic ratio is modified to 3:1, i.e. , 64: 21. And as mentioned we get a close phenotypic ratio of 57: 28 ruby red to standard betta fish ratio.

male

female

R nr R RR Rnr nr Rnr nrnr

Related Questions

Navigate

• Browse (All)
• Browse 2
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.