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7.7 Common Ancestry

2 min readjanuary 13, 2023

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit


AP Biology 🧬

358 resources
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Evolutionary Theories

Similar to using genetic code as an example for evolutionary theory, there are other examples of evidence at the molecular level. There are more structural similarities within the cells of eukaryotes that could help piece together the past. ⌛
Eukaryotes are a diverse group of organisms that include plants, animals, fungi, and protists. One of the key characteristics that sets eukaryotes apart from prokaryotes (bacteria and archaea) is the presence of membrane-bound organelles, such as the nucleus, mitochondria, and chloroplasts. These organelles are thought to have originated through the process of endosymbiosis, where one cell engulfs and incorporates another cell, leading to the evolution of a symbiotic relationship. Yum! 🍔
The presence of membrane-bound organelles in all eukaryotes is considered to be strong structural evidence for their common ancestry.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-6JrJaPtc841i.jpeg?alt=media&token=f6a1da0d-8e62-4dba-b6d6-9bd37e198afc

Source: BioNinja

Another key characteristic of eukaryotes is the presence of linear chromosomes, as opposed to circular chromosomes found in prokaryotes. Linear chromosomes are thought to have evolved as a way to increase the amount of genetic information that can be stored, which would have been beneficial for the evolution of more complex organisms. 🧬
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-jYDeWc6aUe4X.jpg?alt=media&token=861d8a5f-675b-4148-80de-692118525e79

Source: Miami.edu

Eukaryotic genes also contain introns, which are non-coding sequences that interrupt the coding sequences of the gene. Introns are transcribed along with exons, which are the coding sequences, and are then removed by a process called splicing. The presence of introns in eukaryotic genes is thought to have evolved as a way to increase the diversity of proteins that can be produced from a single gene. This is because different exons can be spliced together in different ways, leading to the production of different protein variants.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F420px-Pre-mRNA_to_mRNA_MH-3zx8TCXdXjrE.png?alt=media&token=77d0e9ae-f71e-46e2-b59c-ce4b967ccc51

Source: WikiMedia

In summary, the presence of membrane-bound organelles, linear chromosomes, and genes that contain introns are all characteristics that are unique to eukaryotes and are considered to be strong structural evidence for their common ancestry. These structures and genetic mechanisms have evolved to allow for the complexity of all eukaryotic organisms! ⭐
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-f7ruQs33EKGQ.gif?alt=media&token=2a62cdc0-596b-4272-857e-bd522aff789e

Image courtesy of Giphy.

These similarities are used as evidence to support the evolutionary theory, as it would be nearly impossible for each of these things to develop separately in each animal. It is more likely that these characteristics have continued to be present in eukaryotic cells as organisms continue to evolve.
Check out the AP Bio Unit 7 Replays or watch the 2021 Unit 7 Cram
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