The pedigree in the following figure shows a family in which...

The pedigree in the following figure shows a family in which a rare inherited disease called Leber hereditary optic atrophy is segregating. This condition causes blindness in adulthood. Studies have recently shown that the mutant gene causing Leber hereditary optic atrophy is located in the mitochondrial genome. (GRAPH CANT COPY) a. What other modes of inheritance (e.g., autosomal dominant, $\mathrm{X}$-linked recessive) are consistent with the inheritance of this rare disease? How could you provide evidence that this disease is not inherited using these modes? b. Assuming 11-5 is normal, what proportion of the offspring of II-4 and II-5 are expected to inherit Leber's hereditary optic atrophy? c. Assuming that $11-2$ marries a normal male, what proportion of their sons should be affected? What proportion of their daughters should be affected?

The pedigree in the following figure shows a family in which a rare inherited disease called Leber hereditary optic atrophy is segregating. This condition causes blindness in adulthood. Studies have recently shown that the mutant gene causing Leber hereditary optic atrophy is located in the mitochondrial genome.
(GRAPH CANT COPY)
a. What other modes of inheritance (e.g., autosomal dominant, $\mathrm{X}$-linked recessive) are consistent with the inheritance of this rare disease? How could you provide evidence that this disease is not inherited using these modes?
b. Assuming 11-5 is normal, what proportion of the offspring of II-4 and II-5 are expected to inherit Leber's hereditary optic atrophy?
c. Assuming that $11-2$ marries a normal male, what proportion of their sons should be affected? What proportion of their daughters should be affected?

Key Concepts

Autosomal Dominant Inheritance

In this pattern, only one copy of a mutant allele is needed to exhibit the trait, often causing the phenotype to appear in every generation regardless of gender. The occurrence of the disease in both sexes with a person-to-person transmission pattern can suggest autosomal dominant inheritance; however, if the transmission exclusively follows maternal lines, this mode can be ruled out.

Genetic Prediction of Offspring Outcomes

This concept deals with calculating the expected proportions of affected individuals in the next generation based on the mode of inheritance. It involves understanding and applying probability and Punnett square analyses to predict the likelihood of inheriting the disease, considering factors like carrier status, sex of the offspring, and whether the condition is inherited maternally, autosomally, or via sex-linked patterns.

Mitochondrial Inheritance

This is a mode of genetic transmission where genes are passed solely from the mother via the mitochondria, rather than through the nucleus. In diseases showing mitochondrial inheritance, all offspring of an affected mother may inherit the mutation, while affected fathers do not pass the trait to their children. This concept is crucial in understanding traits that do not conform to classic Mendelian patterns and explains maternal lineage effects seen in pedigrees.

Pedigree Analysis

This involves studying family trees to decipher patterns of trait or disease transmission across generations. Pedigree analysis helps differentiate between various inheritance modes, such as autosomal dominant, autosomal recessive, X-linked, and mitochondrial inheritance. It is essential for interpreting how a disease spreads within a family and provides clues as to whether non-Mendelian mechanisms, like mitochondrial transmission, are involved.

X-linked Inheritance

This term refers to genes located on the X-chromosome and involves distinctive patterns due to differences in male and female sex chromosomes. X-linked recessive conditions typically affect males predominantly while females are carriers, whereas X-linked dominant conditions affect both sexes but often more severely in males. Assessing the sex distribution among affected individuals in a pedigree helps distinguish these patterns from mitochondrial inheritance.

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