Question

6. While you are snorkeling you discover an octopus with very long tentacles and an octopus

with very short tentacles. One is male and the other is female. After a while, they have a whole

bunch of baby octopi who grow up to have intermediate length tentacles. Your friend, who

failed genetics, tells you that this is proof that Mendel was wrong and blending inheritance is

correct. What type of cross should you do now to test your friend’s hypothesis? What are some

other possible explanations for the intermediate length octopi and how would you distinguish

between these hypotheses?

Answer 1

To prove my friend's hypothesis, we can consider that the octopus with long tentacles is homozygous dominant for tentacle length(LL) and the octopus for short tentacles is homozygous recessive (ll). When this cross happens all the offsprings are heterozygous (Ll) and hence their sizes are intermediate from the two parents. Therefore, it can be proved that the blending of phenotypic characters happens during inheritance which contradicts Mendel's Laws.

Another explanation for intermediate length octopi is polygenic inheritance. This kind of inheritance involves two or more genes like in the case of human skin colour. Here, two or more non-epistatic genes interact additively to influence one phenotypic trait.

These two types of inheritance patterns can be distinguished as: in polygenic inheritance, two or more genes contribute to a trait and have equal influence while the alleles for the genes have an additive effect on the phenotype. On the other hand, in incomplete dominance, the phenotype is a mixture of the phenotypes inherited from the parent alleles and only one gene is involved.

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