An excited fluorescent molecule such as GFP or YFP can dispose of the energy from the absorbed photon in either of two ways: 

by fluorescence, emitting a photon of slightly longer wavelength (lower energy) than the exciting light, or 

by nonradiative fluorescence resonance energy transfer (FRET).

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#Unit 5. Developmental Biology

Mammalian fertilization occurs inside the oviducts  of the female

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#Unit 5. Developmental Biology

Translocation of sperm from the vagina to the oviduct involves several processes that work at different times and places:

Sperm motility

Uterine muscle contractions

Sperm rheotaxis

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#Unit 5. Developmental Biology

Sperm rheotaxis 

migrate against the direction of the flow—using

CatSper calcium channels (like sea urchin sperm) to sense calcium influx and monitor the direction of the

current

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#Unit 5. Developmental Biology

The cells of the oviduct induce the sperm to mature, and mammalian sperm complete their development in the female oviducts. This maturation is called capacitation (the gaining of capacity).

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#Unit 5. Developmental Biology

The capacities the sperm gain are those for:

recognizing the cues that will guide them to the egg

undergoing the acrosome reaction

fusing with the egg cell membrane

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#Unit 5. Developmental Biology

Sperm that are not capacitated are “held up” in the cumulus matrix and are unable to reach the egg