Episode 147 – Genetics

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Our understanding of evolution would be incomplete without knowledge of what, deep down, determines the traits of an organism and, crucially, how those traits are passed from parent to offspring. This episode, we discuss the foundational field of Genetics.

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Studying DNA

Genetics is, broadly speaking, the study of genes. And genes are, generally speaking, sections of DNA that code for specific features within a cell.

The basics: DNA is a type of molecule found in the cells of living organisms. The interaction between DNA and other molecules inside the cell leads to the production of proteins that perform the tasks needed within a cell. DNA is packaged into complexes called chromosomes, and a section of DNA that can be linked to a certain function within the cell is called a gene. The entire collection of DNA inside an organism’s cell is called a genome. Genomes can look quite different from one organism to another, and even from cell to cell within an organism.

A simple diagram showing how DNA is packaged into chromosomes (in eukaryotes) and is made up of genes. Image by Thomas Splettstoesser, CC BY-SA 4.0

Throughout the history of genetic science, one of the biggest questions driving research has been: how do organism’s inherit traits from their parents? It’s pretty common knowledge that offspring share features with their parents, but exactly what produces those traits and how offspring inherit them was a big puzzle for a long time. The answer turned out to be (in part) DNA. And since the inheritance of traits is a key part of the evolution of life over time, genetics has become one of the central pillars of the modern study of evolution.

You might recognize this diagram, a Punnett Square, from biology class! The study of how genetic traits give rise to outward features of organisms was a major focus of early figures like Gregor Mendel, and remains an important part of genetics research today.
Image by Madeleine Price Ball

Genetic evolution

Genomes are very complex, and so are the ways they change over time. From one generation to the next, there are many ways organisms’ DNA can build up changes, including mutations caused by outside effects; errors that occur while cells split and duplicate their DNA; the “shuffling” of DNA during cellular reproduction; and even a process called lateral gene transfer, where unrelated organisms swap genes (this is most common in bacteria). All of these processes contribute variation to DNA, making every individual organism’s genome distinct from every other, and that variation allows for evolution over time.

All this change leaves evidence behind in genomes, which scientists can use to decipher evolutionary history. By comparing genomes (typically specific parts of genomes) between organisms, we can interpret which species are more closely or distantly related, just like we do with anatomical features. We also examine rates and patterns of genetic change to better understand the unique evolutionary history of each lineage of life. And if we combine genetic data with fossil data (and sometimes ancient DNA), we can even make estimates about when certain major evolutionary events happened in the distant past using a technique called a molecular clock.

This is an example of an evolutionary tree generated with genetic data.
By statistically comparing genetic structures between numerous species, we can make a hypothesis about how those species are related. That hypothesis takes the form of a phylogenetic tree like this one. Image from Lu et al. 2022

Featured image from Zephyris, CC BY-SA 3.0

Learn more

Essentials of Genetics

From Mendel to epigenetics: History of genetics

Comparative Genomics

The Molecular Clock and Estimating Species Divergence

If you enjoyed this topic and want more like it, check out these related episodes:

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