Question

You are studying hyperactivity in mice. You know that this phenotype is dominant and is determined by just one gene (H) but you need to discriminate between the following alternatives: mitochondrial inheritance, maternal effect, regular nuclear inheritance. You cross female mice from a true-breeding hyperactive strain to males from a true-breeding super-chill strain. All the F_1 progeny is hyperactive. Can you at this point eliminate any of the three modes of inheritance? You cross these hyper F_1 mice to each other, What genotypes and phenotypes (hyper vs. chill) do you expect in their F_2 progeny under each of the three modes of inheritance?

Answer 1

1. In cytoplasmic inheritance gene controlling a given trait is inherited exclusively from the mother.and can be expressed in both male and female progeny.

2. In the case of maternal effect, each individual's phenotype is determined by genotype of the mother. The offspring's phenotype is determined by oocyte of the mother.

3. In the case of regular nuclear inheritance genes controlling a given trait is inherited from nucleus of both male and female parents.

4. In cross between true-breeding hyperactive female with true-breeding super chill male, all the F1 progeny are hyperactive. Because the hyperactive trait is a type of cytoplasmic inheritance.

5. If these hyperactive F1 mice to each other all other the F2 progeny would be with hyperactive trait. Because there is lack of segregation.

6. The hyperactive trait is associated with either organellar DNA (Mitochondrial DNA) or cytoplasmic. The only oocyte of mother contribute this trait and can pass it to F1 and F2 generation.

7. The resulting trait would be either mitochondrial inheritance or maternal effect.