A crest is created when the genes that work to produce feather growth around the neck cause A. the normal feathers to fail to grow creating a blank area that fails in with downy feathers.
B. the feathers to twist as they grow creating the fluffy crest.
C. the feathers to grow under the skin producing a lumpy ridge called a crest.
D. the feathers to grow backwards pushing upward instead of smoothly lying down.
PLEASE HELP ME

Answereather diversity is striking in many aspects. Although the development of feather has been studied for decades, genetic and genomic studies of feather diversity have begun only recently. Many questions remain to be answered by multidisciplinary approaches. In this review, we discuss three levels of feather diversity: Feather morphotypes, intraspecific variations, and interspecific variations. We summarize recent studies of feather evolution in terms of genetics, genomics, and developmental biology and provide perspectives for future research. Specifically, this review includes the following topics: 1) Diversity of feather morphotype; 2) feather diversity among different breeds of domesticated birds, including variations in pigmentation pattern, in feather length or regional identity, in feather orientation, in feather distribution, and in feather structure; and 3) diversity of feathers among avian species, including plumage color and morph differences between species and the regulatory differences in downy feather development between altricial and precocial birds. Finally, we discussed future research directions.

Keywords: feather, skin appendage, genetics, genomics, development, evolution

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Explanation:

d. temperate deciduous forest