A mutation in Arabidopsis immutans results in the necrosis (death) of tissues in a mosaic configuration. Examination of the mitochondrial DNA detects deletions of various regions of the mitochondrial genome in the tissues that are necrotic. When immutans plants are crossed with wild-type plants, the  are wild type, and the  are wild type and immutans in a 3:1 ratio. Explain the inheritance of the immutans mutation and a possible origin of the mitochondrial DNA deletions.

Verified step by step guidance

1. span>1. Understand the phenotype: The immutans mutation in Arabidopsis results in necrotic tissues in a mosaic pattern, indicating a possible issue with cellular respiration or energy production, often linked to mitochondrial function.
2. span>2. Analyze the genetic cross: When immutans plants are crossed with wild-type plants, the offspring show a 3:1 ratio of wild type to immutans phenotype. This suggests a Mendelian inheritance pattern, likely involving a single nuclear gene with a dominant wild-type allele.
3. span>3. Consider mitochondrial DNA: The presence of deletions in mitochondrial DNA in necrotic tissues suggests that these deletions may contribute to the immutans phenotype. Mitochondrial DNA is inherited maternally, but the phenotype is not strictly maternal, indicating nuclear control.
4. span>4. Hypothesize the mutation's effect: The immutans mutation could be in a nuclear gene that encodes a protein essential for mitochondrial function, leading to mitochondrial DNA instability or damage in certain cells, causing the mosaic pattern.
5. span>5. Propose a mechanism: The nuclear gene mutation might impair a protein involved in mitochondrial DNA replication or repair, leading to deletions in mitochondrial DNA and resulting in the observed necrotic phenotype in a subset of cells.

Key Concepts

Mitochondrial Inheritance

Mitochondrial inheritance refers to the transmission of genetic material found in mitochondria, which is typically inherited maternally. In plants, mutations in mitochondrial DNA can lead to phenotypic changes, such as tissue necrosis. Understanding this concept is crucial for analyzing how the immutans mutation affects the offspring and how mitochondrial deletions may arise.

Genetic Mutations

Genetic mutations are alterations in the DNA sequence that can lead to changes in phenotype. In the case of the immutans mutation, it results in a specific phenotype characterized by necrotic tissues. Recognizing the types of mutations, such as deletions, and their effects on gene function is essential for explaining the observed inheritance patterns and phenotypic ratios.

Mendelian Ratios

Mendelian ratios describe the expected proportions of different phenotypes in the offspring of a genetic cross, based on Mendel's laws of inheritance. The 3:1 ratio observed in the immutans cross suggests a single gene with two alleles, where one is dominant (wild type) and the other is recessive (immutans). This concept helps in understanding how the immutans mutation segregates in the offspring and the implications for mitochondrial DNA deletions.