Much change is due to random genetic drift rather than positive selection.

许多生物变化源于基因的随机漂变而非主动选择.

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The MHC restriction of T cell is determined in positive selection.

阳性选择决定了成熟T细胞的MHC限制性,阴性选择使机体获得自身免疫耐受.

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Besides HA sequence, positive selection can also be found on NA sequence.

除HA外, NA序列在进化中也存在正向选择位点,对于该序列的进化规律值得进一步研究.

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