Effect of change in yolk amount and distribution on pattern of cleavage

Yolk is a nutrient-rich substance present in the egg that provides nourishment to the developing embryo. The amount and distribution of yolk in the egg can have a significant effect on the pattern of cleavage, which refers to the series of cell divisions that occur after fertilization.

As the yolk content increases, the egg becomes more massive and the distribution of the yolk becomes uneven. This can result in a change in the pattern of cleavage, as the blastomeres (cells formed by cleavage) are influenced by the distribution of the yolk.

The following are the effects of change in the amount of yolk and its distribution on the pattern of cleavage:

1. Holoblastic vs. meroblastic cleavage

Holoblastic cleavage occurs in eggs that have little yolk, resulting in the formation of blastomeres that are roughly equal in size. Meroblastic cleavage occurs in eggs that have a large amount of yolk, resulting in the formation of a blastodisc (a disk-shaped structure) that develops into the embryo while the yolk remains relatively intact.

2. Radial vs. spiral cleavage

Radial cleavage occurs in eggs that have little yolk and results in the formation of blastomeres that are arranged in a radial pattern. Spiral cleavage occurs in eggs that have a moderate amount of yolk and results in the formation of blastomeres that spiral around the embryo.

3. Asynchronous vs. synchronous cleavage

Asynchronous cleavage occurs in eggs that have a large amount of yolk and results in an uneven distribution of blastomeres, with some cells dividing faster than others. Synchronous cleavage occurs in eggs that have little yolk and results in the formation of blastomeres that divide at the same rate.

Conclusion

In summary, a change in the amount of yolk and its distribution in the egg can have a significant effect on the pattern of cleavage. This can result in differences in the number of blastomeres produced, fertilization, and the formation of the zygote. Therefore, the pattern of cleavage is an important developmental process that is influenced by the amount and distribution of yolk in the egg.