Because all organisms are made up of cells and there are different types of cells which carry different functions.
Organ System, Organ coll, tissue
The water cycle is a parameter of the hydrosphere that always remains constant. Life on Earth and its sustenance is possible because of this cycle. The continuous evaporation, condensation, and precipitation of water provides for the many processes involved in Earth's natural surroundings. Without the water cycle, life would cease to exist.
Answer:
It is possible to compare the expression of homologous genes in the brain of <em>D. melanoganster</em> and humans, because the expression levels of conserved genes may be associated with the evolution of cognitive features such as complex learning and memory.
Explanation:
Model organisms can be used to understand the patterns and processes that affect human evolution. <em>Drosophila melanogaster </em>is a model organism that has been used to study expression patterns of conserved genes in the course of evolution. This model organism has also been used to develop genetic mutant lines in order to examine the role of genes evolutionarily conserved in animals, including those involved in neurocognitive development.
In genetic research, an experiment as the above described is framed in a research field named 'Behavioral Genetics', which is a discipline that studies how evolutionarily conserved gene networks may be associated with neurocognitive tasks during brain evolution.
