How Rate, Timing & Spatial Arrangement Affect Developmental Genes

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  • 0:01 Developmental Genes
  • 1:18 Rate & Timing
  • 2:19 Spatial Arrangements
  • 4:04 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Your adult form is the result of your development. This important life stage is not only influential on how you develop as an individual, but also how new species arise and develop as well.

Developmental Genes

When we think of evolution, we tend to think of changes that happen to a population in the adult stages of organisms because this is the stage of life that what we see. But even seemingly insignificant evolutionary changes in developmental genes or the genes that control the rate, timing, and pattern of changes in an organism are the ones that often lead to major morphological differences between species.

Think of developmental genes like directions along a road map. One set of directions says to take I-75 north from Tampa, Florida, and make a slight left onto I-10 west. A different set of directions doesn't include this turn, so you stay on I-75 the entire way. This is a very small difference in the directions: one veers left the other stays straight. But your end destination is quite different! With the first set of directions you end up in L.A., while with the second set of directions you end up in northern Michigan!

If we go back to developmental genes, you can see how even one simple change like the one in our road map can lead to a drastically different organism somewhere down the line. And while we don't have left and right turns guiding our development, we do have other sets of instructions that tell our cells what to do and when.

Rate and Timing

Changes in the rate and timing of developmental events have a major influence on how organisms evolve differently from each other. Simply put, both when and which events occur, as well as the rate at which those events occur, influence how we end up down the line as fully developed individuals. Take for example humans and chimps. We share most of our genes with this relative, but looking at us from the outside you can see a clear difference, and one thing that leads to this is the rate at which our skulls grow.

As fetuses, our skulls are actually quite similar to those of chimps. But as we grow into adults, the chimps' jaws grow much faster than those of humans, which draws down the forehead and elongates the face. Because of genetic changes in humans, we have a much slower jaw growth, giving us an adult jaw that is much more proportional to the rest of the head. Our brains also grow much faster after birth, giving us a larger skull than chimps, whose brains grow much slower.

Spatial Arrangements

In addition to the rate and timing of genetic events, our development is also influenced by where those changes occur. In other words, where certain genes are expressed (or not expressed). Imagine if our highway was built incorrectly. Instead of an off-ramp being placed so that it leads to a city it leads to the middle of a lake. Not very useful, and it doesn't get you where you need to go!

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