Parrots and Dogs are able to generate internal heat to maintain their body temperature in a coid environment. Parrots and Dogs are Endotherms. They generate most of the heat they need internally, when it's cold outside.
Explanation:
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"An organism in which the two copies of the gene are identical — that is, have the same allele — is called homozygous for that gene. An organism which has two different alleles of the gene is called heterozygous."