Final Answer:
The missing genes in present-day mitochondria were transferred to the nuclear genome over evolutionary time through a process known as endosymbiotic gene transfer.
Step-by-step explanation:
Mitochondria are believed to have originated from free-living bacteria that formed a symbiotic relationship with early eukaryotic cells. During this evolutionary process, many mitochondrial genes essential for survival gradually migrated to the host cell's nuclear genome.
This phenomenon is known as endosymbiotic gene transfer. The transfer of genes from the mitochondrial genome to the nuclear genome conferred several advantages, such as enhanced control over gene expression and protection of essential genetic information.
The endosymbiotic theory proposes that a primitive host cell engulfed a free-living bacterium, giving rise to the ancestral mitochondrion. Over time, as the symbiotic relationship evolved, the host cell and the engulfed bacterium became mutually dependent.
To streamline cellular functions and optimize energy production, the host cell selectively retained certain mitochondrial genes while transferring others to its nuclear DNA. This transfer allowed the host cell to regulate mitochondrial functions more effectively and coordinate cellular activities.
As a result, present-day mitochondria have a significantly reduced genome, containing only a fraction of the genes found in their bacterial ancestors. The majority of mitochondrial proteins are now synthesized in the cell's cytoplasm and imported into the mitochondria.
This intricate process highlights the dynamic interplay between the host cell's nuclear genome and the remnants of the ancestral mitochondrial genome, shaping the modern-day structure and function of mitochondria.