Download 1. What is epigenesis?

Study Questions:
1. What is epigenesis?
Study Questions:
1. What is epigenesis?
Epigenesis is the creation of structures that did not exist before. In embryology, it is more
appropriately called “epigenetics”, which is the formation of structures based on the
genetic plan encoded in the DNA. So, from a single fertilized egg that doesn’t have a
nervous, circulatory, or digestive system (obviously), cells divide and specialize and form
these systems in a multicellular animal.
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
In a descriptive sense, they appear similar. Over evolutionary time within a group, we see
the appearance of organisms with new structures that ancestors did not have – like
amphibians with feet evolving from fish that lack feet, and birds with wings evolving from
reptiles without wings. Embryologically, we see similar patterns, where complex
structures are produced from simpler stages that lack these structures: so human embryos
lack limbs early in development, and then grow limbs later in development.
Developmentally, we understand that these changes are due to the turning on of
particular genes. The evolution of these structures in the first place is probably tied to the
formation and activation of these genes, as well.
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
In both cases, functional units are replicated. This allows for modification of one unit
without compromising the original function of the other unit. This allows for both
ADDITION of function, to do something new, and SPECIALIZATIONof function, to allocate
specific function to particular units to increase efficiency.
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
4. What are homeotic genes, and what type of protein do they code for?
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
4. What are homeotic genes, and what type of protein do they code for?
Homeotic genes are genes that encode proteins with a specific “homeotic” sequence,
called a “homeobox”. This sequence is a DNA binding domain, which allows the protein to
bind to DNA. Homeotic genes code for homeotic proteins, that are transcription factors.
They bind to promoter regions and turn on genetic cascades involved with body
region/segment development.
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
4. What are homeotic genes, and what type of protein do they code for?
5. Explain homologous structures in terms of the regulation of developmental genes.
Study Questions:
1. What is epigenesis?
2. Explain the relationship between development and evolution.
3. How are gene duplication and segmentation similar in terms of introducing
evolutionary novelty?
4. What are homeotic genes, and what type of protein do they code for?
5. Explain homologous structures in terms of the regulation of developmental genes.
Homologous structures are build from the same body parts, but have different functions in
different environments. The forelimbs of mammals are an example. Humans, cats, bats,
and whales all have one bone in the upper ‘arm’ (humerus), two bones more distal (radius
and ulna), wrist bones, and digits. This skeletal structure occurs, regardless of whether the
forelimb is a grasping hand, a running paw, a flying wing or a swimming flipper. The
difference between these structures is only in the relative sizes of the bones. Bats have
long digit bones relative to the radius and ulna, compared to cats and humans. However,
they are obviously the same bones. These differences in relative size occurs because of
differences in the rates of growth of the bones – differences in allometry. These
differences are developmental – orchestrated by differences in the activity of
developmental genes in these different bones.