2. Mendel's Laws of Inheritance

(a) In humans the mitochondrial genome encodes a low number of proteins, rRNAs, and tRNAs but imports approximately 1100 proteins encoded by the nuclear genome. Yet, with such a small proportion from the mitochondrial genome encoding proteins and RNAs, a disproportionately high number of genetic disorders due to mtDNA mutations have been identified [Bigger, B. et al. (1999)]. What inheritance pattern would you expect in a three-generation pedigree in which the grandfather expresses the initial mtDNA defect? What inheritance pattern would you expect in a three-generation pedigree in which the grandmother expresses the initial mtDNA defect? (b) Considering the description in part (a) above, how would your pedigrees change if you knew that the mutation that caused the mitochondrial defect was recessive and located in the nuclear genome, was successfully transported into mitochondria, and negated a physiologically important mitochondrial function?

The following pedigree shows a family in which several individuals exhibit symptoms of the mitochondrial disease MERRF. Two siblings (II-2 and II-5) approach you to inquire about whether their children will also be afflicted with MERRF. What do you tell them? 

What is the most likely mode of inheritance for the trait depicted in the following human pedigree? 

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person                 Condition           Percent Mitochondria with
                                                       Mutation
Proband                A and PN            >90%
Brother                  A and PN            >90%
Brother                  Asymptomatic      17%
Mother                   PN                       86%
Maternal uncle       PN                       85%
Maternal cousin     A and PN             90%
Maternal cousin     A and PN             91%
Maternal                Asymptomatic      56%
grandmother


In what way does a condition caused by mtDNA differ in expression and transmission from a mutation that causes albinism?

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person                 Condition           Percent Mitochondria with
                                                       Mutation
Proband                A and PN            >90%
Brother                  A and PN            >90%
Brother                  Asymptomatic      17%
Mother                   PN                       86%
Maternal uncle       PN                       85%
Maternal cousin     A and PN             90%
Maternal cousin     A and PN             91%
Maternal                Asymptomatic      56%
grandmother


How can some individuals in the same family show such variation in symptoms? What term, as related to organelle heredity, describes such variation?

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person                 Condition           Percent Mitochondria with
                                                       Mutation
Proband                A and PN            >90%
Brother                  A and PN            >90%
Brother                  Asymptomatic      17%
Mother                   PN                       86%
Maternal uncle       PN                       85%
Maternal cousin     A and PN             90%
Maternal cousin     A and PN             91%
Maternal                Asymptomatic      56%
grandmother


Provide an explanation for the pattern of inheritance of the disease. What term describes this pattern?

Researchers examined a family with an interesting distribution of Leigh syndrome symptoms. In this disorder, individuals may show a progressive loss of motor function (ataxia, A) with peripheral neuropathy (PN, meaning impairment of the peripheral nerves). A mitochondrial DNA (mtDNA) mutation that reduces ATPase activity was identified in various tissues of affected individuals. The accompanying table summarizes the presence of symptoms in an extended family.

Person                 Condition           Percent Mitochondria with
                                                       Mutation
Proband                A and PN            >90%
Brother                  A and PN            >90%
Brother                  Asymptomatic      17%
Mother                   PN                       86%
Maternal uncle       PN                       85%
Maternal cousin     A and PN             90%
Maternal cousin     A and PN             91%
Maternal                Asymptomatic      56%
grandmother


Develop a pedigree that summarizes the information presented in the table.

For each pedigree shown,

Determine which other pattern(s) of transmission is/are possible. For each possible mode of transmission, specify the genotypes necessary for transmission to occur. <>

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,

Give the genotype(s) possible for each member of the family, assuming the trait is autosomal recessive. 

The accompanying pedigree shows the transmission of a phenotypic character. Using B to represent a dominant allele and b to represent a recessive allele,

Give the genotype(s) possible for each member of the family, assuming the trait is autosomal dominant.