BIOLOGY 1M03 Lecture Notes - Lecture 26: Wisdom Tooth, Kin Selection, Antimicrobial Resistance
29 Jun 2018
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Are there other closely related species for which we know more?
In situ hybridization illustrates variation in Bmp4 expression in finch embryos
corresponds with variation in beak morphology
What genes were actually involved in this natural selection event, and how
are they affected? So in thinking especially of 80s about what we knew about
the genomes, and the genetic of finches. The answer is very little.
These days we can go in my lab and sequence a genome quite quickly, those
days technology was different. We don’t even have a complete genome of
humans, let alone of finches. Not much known about finches but we have
been studying several other things that are closely related to finches, and we
knew a lot about them. For example, chickens, we eat chickens and people
had been studying chickens for a long time and we knew quite a lot of them.
They were used to model organism to study limb development and also even
head development. So we actually knew from studies fo chickens that there
was a gene called BMP4 that influenced bill shape and size in chickens. This
lead Grant and their collobartes to think BMP4 as a candidate gene, a
candidate for natural selection. So what they did was to explore patterns of
gene expression of this gene in the finches, because they knew that the same
homologous version in chickens influenced beak morphology in chickens. The
question is that, the same gene act in the same way in finches? They used a
technique called in situ hybridization, but basically what it allows you to do is
to quantify how much of a particular gene is expressed during development.
So what we see on the top are two different species in the embryonic stage,
they opened the embryo and they treated slices of this embryo with a
chemical reaction that basically makes sections darker that express BMP4 at
a high level. So the RNA for BMP4 is present in some cells, and those cells
will get dark because of the chemical reaction and the areas where BMP4 is
not expressed, it will look light. What you can see on the top is that there are
dark areas, it’s the head of the embryo, its fairly light in this species on left,
but there’s a dark patch on the right, they were able to visualize the RNA
expression using In situ hybridization and they found that the level of
expression was higher in species that tended to have a thick beak. These two
have different widths of their beaks, one on left is narrow, right is wide. The
level of expression inferred of this gene was higher in species with thick
beaks. if you didn’t do the in situ hybridization you just looked, without
chemical treatment, you wouldn’t see a dark patch.
Ectopic expression of Bmp4 also changes beak morphology in chicken
They then asked well this is correlation and causation do we really know that,
that’s the cause of the thick bill or is just a correlation. The relationship
between BMP4 expression level and thickness of beaks, so to test that they
ectopically or artificially manipulate BMP4 expression in chickens. So that’s
why this shows, these are not finches these are chickens. What they did was
this is a normal chicken, wild type and they manipulated the level of BMP4
expression at a key developmental stage and they were able to see the thick
beaks in chickens. They basically artificially up regulated the expression in
chickens and caused a developmental trajectory of the beaks, in the
find more resources at oneclass.com
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Document Summary
In situ hybridization illustrates variation in bmp4 expression in finch embryos corresponds with variation in beak morphology. So in thinking especially of 80s about what we knew about the genomes, and the genetic of finches. These days we can go in my lab and sequence a genome quite quickly, those days technology was different. We don"t even have a complete genome of humans, let alone of finches. Not much known about finches but we have been studying several other things that are closely related to finches, and we knew a lot about them. For example, chickens, we eat chickens and people had been studying chickens for a long time and we knew quite a lot of them. They were used to model organism to study limb development and also even head development. So we actually knew from studies fo chickens that there was a gene called bmp4 that influenced bill shape and size in chickens.
