Once you are done with this lesson you should be able to: 1  Identify the Abbasids. 2  Describe the roles of the caliphs and the viziers. 3  Explain how the caliphs' focus on trade led to the Golden Age of Islam. 4  Summarize the fall of the Abbasids.
Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each personâs unique physical features. Genes are made up of DNA.Each chromosome contains many genes. A gene is the basic physical and functional unit of heredity. Genes, which are made up of DNA, act as instructions to make molecules called proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.lleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each personâs unique physical features. Genes are made up of DNA.
1 Chromosome: a long, thread-like molecule made of the chemical called DNA (deoxyribonucleic acid) that is held together with special proteins and is visible (with strong microscopes) during cell division... 2  more. 3  Gene: a region of DNA where a specific set of instructions for one trait is kept.