In this chapter, we focused on extranuclear inheritance and how traits can be determined by genetic information contained in mitochondria and chloroplasts, and we discussed how expression of maternal genotypes can affect the phenotype of an organism. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions?

What observations support the endosymbiotic theory?

Key Concepts

Endosymbiotic Theory

The endosymbiotic theory posits that certain organelles, specifically mitochondria and chloroplasts, originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells. This theory explains how these organelles have their own DNA, which is similar to bacterial DNA, supporting the idea that they were once independent entities. The theory is crucial for understanding the evolution of eukaryotic cells and the role of these organelles in cellular function.

Extranuclear Inheritance

Extranuclear inheritance refers to the transmission of genetic material that occurs outside the nucleus, primarily through organelles like mitochondria and chloroplasts. This type of inheritance is typically maternal, meaning that offspring inherit these organelles and their associated genes from the mother. Understanding this concept is essential for analyzing how traits can be influenced by maternal genotypes and how they differ from Mendelian inheritance patterns.

Phenotype and Maternal Genotypes

The phenotype of an organism is the observable physical or biochemical characteristics determined by its genotype and environmental influences. Maternal genotypes can significantly affect the phenotype of offspring, especially in cases of extranuclear inheritance, where traits linked to mitochondrial or chloroplast DNA are passed down. This relationship highlights the importance of maternal contributions to the genetic makeup and traits of the next generation.