In the discussion, 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?

Verified step by step guidance

1. Understand the endosymbiotic theory: This theory proposes that mitochondria and chloroplasts originated from free-living prokaryotic organisms that were engulfed by ancestral eukaryotic cells, forming a symbiotic relationship.
2. Examine the structural evidence: Mitochondria and chloroplasts have double membranes, which is consistent with the engulfing process described in the theory. Their inner membrane resembles that of prokaryotes, while the outer membrane resembles the host cell's membrane.
3. Analyze genetic evidence: Both mitochondria and chloroplasts contain their own circular DNA, similar to bacterial genomes, and they replicate independently of the host cell's nucleus. This supports their prokaryotic origin.
4. Consider ribosomal evidence: The ribosomes found in mitochondria and chloroplasts are similar in size and structure to bacterial ribosomes, rather than eukaryotic ribosomes, further supporting the theory.
5. Review biochemical and functional evidence: Mitochondria and chloroplasts perform processes (e.g., oxidative phosphorylation and photosynthesis) that are similar to those carried out by certain prokaryotes, indicating a shared evolutionary history.

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, and how they replicate independently of the cell's nuclear DNA, supporting the idea of a symbiotic relationship that led to the evolution of complex cells.

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 genetic information exclusively from the mother, which can significantly influence traits and phenotypes in the progeny.

Maternal Effect

The maternal effect is a phenomenon where the genotype of the mother directly influences the phenotype of her offspring, regardless of the offspring's own genotype. This effect is particularly relevant in the context of extranuclear inheritance, as maternal genotypes can determine the characteristics of organelles passed to the offspring, thereby affecting traits such as metabolism, growth, and development.