G. Hatching/birth 2. Fill in the following table with what you know about each o

Question

G. Hatching/birth 2. Fill in the following table with what you know about each of the species we studied Species Starfish Frog Chick Human Relative amount of yolk Relative size of the egs Time to Hatching/Birth Fertilization Internal or External? Presence of free-living larval stage? 3. How does the quantity of yolk found in an egg at the time of fertilization alter cleavage patterns? Taken from: Dr.Pacricia Cassin and Dr. Catherine Kelly, Embryologs" in From Cel to Plane. D. Betty Borowsky, editor 122508CLEAVAGE 4 6-22

Explanation / Answer

b. Since yolk when present occupies large space within the egg and limits the mitotic division to a smaller part of egg. As such, the rate and pattern of cleavage is impacted. Yolk is itself no living and does not divide. The cleavage is therefore of two types :1:holoblastic:when yolk is absent, the zygote divides completely into two blastomers, 2:meroblastic :when yolk is present in bulk, the cleavage is limited to a small area near animal pole called blastodisc.

Species starfish frog chick human Relative amount of yolk microlecithal macrolecithal megalecithal alecithal Relative size of egg tiny small large microscopic Time to hatching 1 day 6-21days 21days 9 months Fertilization external external internal internal Larva yes yes no no

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