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Genetic inheritance is the process by which genes and traits are passed from parents to their offspring. It can be thought of as nature's way of keeping historical records within organisms. This record includes traits that might no longer be visible in an organism but are still present in their genetic code. When looking at modern-day species, like baleen whales, which have genes for teeth even though they do not have teeth, we can appreciate this concept.
Baleen whales inherited tooth genes from their ancestors who once had teeth. Over time, these genes have lost their function because they are not needed for survival anymore. However, due to the nature of inheritance, they are still passed down.

• Genetic inheritance involves receiving a mixture of genes from both parents.
• Even traits or functions not apparent can exist as non-functional or vestigial genes.
• These vestigial genes act as evidence of evolutionary ancestry.

Gene function refers to the roles that specific genes play in the development and maintenance of an organism. Each gene usually holds instructions for building proteins that perform crucial functions inside cells. However, not all genes are active or necessary throughout the lifetime of an organism.
In cases like the baleen whales, the genes responsible for building teeth are known as non-functional or pseudogenes. These genes have undergone mutations that have rendered them inactive but they still exist in the genome. This happens because evolution does not immediately eliminate genes that are no longer functional.
Non-functional genes can result from:

• Gene mutations that prevent proper expression.
• The lack of evolutionary pressure to maintain the gene's function due to changes in an organism's lifestyle or diet.
• Random genetic drift which makes the loss of function acceptable.

Evolutionary biology examines the processes by which species change over time. It involves understanding how gene frequencies shift within populations and how traits are lost or gained. This field provides a lens to understand why baleen whales still carry genes for teeth. These remnants illustrate how evolution is not a perfect "editing" process.
Evolutionary biology proposes that as species adapt to new environments or lifestyles, certain traits may become less essential or useful. For baleen whales, as they adapted to a filter-feeding lifestyle that required no teeth, the pressure to maintain functional tooth-building genes disappeared. Consequently, these genes became non-functional but were not immediately removed from the genome.
Ideas central to evolutionary biology include:

• Natural selection which favors traits that improve survival and reproduction.
• Genetic drift that causes random changes in gene frequencies.
• Gene flow where genes are transferred between populations, affecting evolutionary paths.
• Vestigial structures and genes that serve as evolutionary "leftovers."