Question

Question 4. Consider three person embryos – which are designed for couples with a female who carries mitochondrial mutations. In the process, we learned that two women can both have the same mitochondrial DNA mutation – but have radically different phenotypes.

(A) Explain/Describe how two individuals with the same mitochondrial mutation can have different phenotypes. Consider one woman with the mitochondrial mutation in part (A). She has no phenotypic abnormality, but is told she should consider the three person embryos to ensure her children don’t risk disease.

(B) Explain how it is possible her offspring are at risk if she has no phenotypic abnormality?

(C)Describe how it is possible that a mutation could result in paternal inheritance of mitochondrial DNA. To help, consider why you (probably) don’t have any mitochondria inherited from your father.

Answer 1

A) A person exhibiting same kind of mutation might not be able to express in its phenotype and this is called a variable expression of genes.. When two person carry the same mutation they might not show the same phenotype. The reason is penetrance and expressivity.

Variable expressivity can be due to:

a) modifier genes,

b) environmental factors,

c) allelic variation

d) complex genetic and environmental interactions.

A genetic modifier when expressed is able to alter the expression of another gene. They can affect phenotypes at other levels of organization by altering phenotypes at cellular organismal level.

B)   Maternal effect happens because the trait is recessive here and mutation occurs, so the female homozygous for mutation appears normal phenotypically but her offsprings shows phenotypes that are mutant and visible even if they are heterozygous for the mutation.

C) heteroplasmy is a form of inheritance of maternal DNA. It results in mutation and studies have found there is biparental inheritance of mt DNA in a person's muscle tissues.