This second video (playing below) shows both the surface contraction
wave and gravitational rotation. The wave is best viewed on a fast computer with
a fast internet connection. Note the wave crosses the cell from left to right (where did the sperm enter?) and then around 9-10 min, the cell rotates
(gravitational rotation).
Insemination was at time zero. A second wave is starting as the video ends at about 15 min after insemination. I captured one image every 20 sec and the replay is at 10 frames per sec. The zygote is about 1.25mm across.
Don't confuse this gravitational rotation (that occurs within 15 min of
fertilization) with cortical rotation (occurs about an hour after
fertilization). In cortical rotation, the only external event that can be
seen is the appearance of the grey crescent (impossible to see clearly with
Xenopus eggs, but can be seen with other amphibian species). David Gard at
the University of Utah also a web site with pictures of gravitational rotation
(see his "DB cinema").
What causes the gravitational rotation?
What would happen if this were conducted on the Space shuttle (it has been...)?
Does the embryo develop normally without gravitational rotation? This leads to:
what is one possible purpose of the gravitational wave?
How fast is the surface wave in this second video of a different cell? Is the
rate of travel of the wave similar in both videos? (two different cells were
used)
when does the gravitational rotation begin (min after fertilization) and how
fast is the gravitational rotation (how would you measure it? distance? angle?
per time).
Is this rate of gravitational rotation similar to that shown in the video of the
group of cells (see home page)?
Is the Xenopus wave faster or slower than the calcium wave in sea
urchins? Find the calcium wave in sea urchins at .....
What is the relationship between the surface wave and the calcium wave?
What is the relationship between where the sperm enters, which way the wave
moves and the way the zygote rotates?