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Chapter 20

BIOA01H3 Chapter 20: Notes

Biological Sciences
Course Code
Mark Fitzpatrick

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Chapter 20: Genes and Development
Gene expression in the development off organisms is hierarchical pattern. This means that one gene’s
activation triggers another’s in a chain reaction.
Regionalization and Specialization in Evo-Devo
Apart from genes only being hierarchical, they must also have the correct pattern and type of cells in
different parts of the embryo. There are 3 classes of genes that are responsible for pattern formation.
They include:
Maternal-effect genes
Segmentation genes
Segment Polarity genes
Homoeotic genes
Maternal-Effect Genes
The Drosophila Fly
The embryonic development of the Drosophila fly is important for hierarchical control development.
Unlike mammals, the fly doesn’t have a zygote uses cell division. Instead, a concentration of nuclei
found in the center of the egg form a preliminary developmental structure (found in animals where it is
called a blastocyst) called a cellular blastoderm.
Hierarchical still
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