Answer:D
Explanation: The pulmonary air sacs of birds only permit a unidirectional flow of air through the lungs. Unidirectional flow means that air is inhale and exhale through one trachea alternatively. This means the bird lungs only receive largely fresh air which has a high oxygen content during inhalation and do not receive fresh during exhalation. While air flow bidirectional in mammals.
Answer:
undergo irreversible repression
Explanation:
Cellular differentiation refers to the process by which one cell and/or cell population divides and differentiates into more specialized cells. During cell fate differentiation, epigenetic marks modify chromatin structure in order to hamper the accessibility of the transcriptional machinery and transcriptional factors to different genes, which are irreversibly repressed. These epigenetic marks include DNA methylation and histone modifications (e.g., histone acetylation, histone methylation, etc). For example, it has been shown that DNA methylation and histone H3 lysine 27 tri‐methylation (H3K27me3) are epigenetic repressive marks on genomic regions that play a major role in gene expression programs during cell fate differentiation.
Explanation:
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<h3>I couldn't find anything else.</h3>
The insertion or deletion of 2 or more nucleotides would cause a frame shift mutation .