Question

Maternal effect 2 m/+ x oʻmit mit x oʻmim O m/m x Oʻmit m/m * ©*+/+ • m/m A m/m Am/+ m/+ • m/+ • +/+ • m/m • m/+ All offspring show the wild-type phenotype All offspring show the mutant phenotype Genetic crosses involving a maternal effect recessive mutation, m. The maternal genotype determines the phenotype of the offspring.

Please explain the concept and how it does not follow Mendelian Inheritance

Answer 1

Maternal effect is a type of non mendelian inheritance because the phenotype of the progeny is dependent upon the genotype of the mother.

In mendelian inheritance, the phenotype of the progeny is dependent upon the genotype of the progeny which is further determined using the genotypes of the mother and father.

But in this case only mother is responsible for the phenotype seen in the progeny.

If you look at the given example carefully, then in the first column all the progenies are showing wild-type phenotype. This is because every progeny has received one allele from the mother and one allele from the father. And because the wild-type allele was dominant over the mutant allele, all the progeny were wild-type in phenotype.

If maternal effect was not there, and this example simply shows mendelian inheritance, then also all the progenies would be having wild type phenotype. So we cannot differentiate between mendelian inheritance and maternal effect using only wild-type phenotype. Therefore the image is also showing another example of mutant phenotype.

In the second column, you can see that the mother is mutant and the father is wild type. If this was a mendelian inheritance, then all the progenies would have wild-type phenotype. But because only mother is responsible for the phenotype of the progeny, and the mother is mutant in this case, therefore the progenies will also be mutant.

So, in case of maternal inheritance, only and only the genotype of mother is responsible for determining the phenotype of the progeny. No matter what is the genotype of the progeny, because the progeny is receiving 1 allele from the mother and one allele from the father also. So you do not have to look at the genotype of the father or genotype of the progeny. Only look at the genotype of the mother. If the genotype of the mother is wild type, then the progeny will also look wild-type or if the genotype mutant, then the progeny will also be mutant.

I hope you understood.

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