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They have moist scaleless skin which is used to supplement the lungs in gas exchange.
The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water.
amino acid sequence: A series of amino acids, the building blocks of proteins, usually coded for by DNA.
Exceptions are those coded for by the RNA of certain viruses, such as HIV.
In a diploid cell there are usually two alleles of any one gene (one from each parent).