Question

You study eye formation using Mexican cave-dwelling blind fish. You know that blindness is a trait controlled by multiple genes and inherited in a recessive manner. A blind fish from a true-breeding line in one cave was crossed to a blind fish from a true-breeding line in anothercave. If the mutation that causes blindness is in two different genes in the two fish, you should see:

Answer 1

Answer:

The whole progeny will be not-blinded. All the individuals in the F1 will be able to see.          

Explanation:  

Multiple genes can affect the same trait. Two blind fishes can produce not-blinded offspring because parents have mutations in two different genes. This is a case of complementation. When parents have a mutation in the same gene, this process is known as non-complementation, and in these cases, their progeny will exhibit the mutated trait.

We know that blindness is a trait controlled by multiple genes and inherited in a recessive manner. So we need at least two genes to have not-blinded eyes, and in the exposed example the mutation that causes blindness is in fact in two different genes.

So let´s say that genes B and E are two genes involved in eye formation and that their respective recessive alleles will express blindness. Then:

Cross: A blind fish from a true-breeding line in B gene crossed to a blind fish from a true-breeding line in E gene.

Parental) BB ee   x   bb EE

Gametes) Be   Be   Be   Be

                 bE   bE   bE  bE

Punnet square)    Be      Be      Be      Be

                   bE   BbEe  BbEe  BbEe  BbEe

                   bE   BbEe  BbEe  BbEe  BbEe

                   bE   BbEe  BbEe  BbEe  BbEe

                   bE   BbEe  BbEe  BbEe  BbEe

F1) 100 %  BbEe, heterozygote for both genes. None of the F1 individuals are blind.                

Answer 2

If the mutation that causes blindness is in two different genes in the two fish, it is expected that NONE of the offspring are blind.

• In diploid organisms, an individual receives two different gene forms or alleles for each gene locus, one from the mother and the other allele from the father.

• An individual is homo-zygous when it receives the same allele from both parents, whereas an individual is heterozygous when it receives different alleles from both parents.

• In cases of complete dominance, an allele is said to be recessive when it is completely masked by the dominant allele in heterozygous individuals.

• In this case, the blindness trait is controlled by multiple genes which are inherited in a recessive pattern, thereby a cross between a blind fish from a true-breeding line will produce double heterozygous (not blind) individuals.

In conclusion, if the mutation that causes blindness is in two different genes in the two fish, it is expected that NONE of the offspring are blind.

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