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In a diploid cell there are usually two alleles of any one gene (one from each parent).
Within a population there may be many different alleles of a gene; each has a unique nucleotide sequence.
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.
The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land.analogous structures: Structures in different species that look alike or perform similar functions (e.g., the wings of butterflies and the wings of birds) that have evolved convergently but do not develop from similar groups of embryological tissues, and that have not evolved from similar structures known to be shared by common ancestors. Note: The recent discovery of deep genetic homologies has brought new interest, new information, and discussion to the classical concepts of analogous and homologous structures.anatomy: (1) The structure of an organism or one of its parts. ancestral homology: Homology that evolved before the common ancestor of a set of species, and which is present in other species outside that set of species. anthropoid: A member of the group of primates made up of monkeys, apes, and humans.antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.
aperture: Of a camera, the adjustable opening through which light passes to reach the film.
allometry: The relation between the size of an organism and the size of any of its parts.