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Introduction:
A zygote is a single-celled eukaryotic cell that is formed as the result of fertilization between two gametes. It undergoes mitosis to form an embryo that further develops into a multi-celled eukaryotic organism. The division of cells in the early embryonic stage is known as cleavage.
Answer to Problem 1TYK
Correct answer:
The major contributors to the cleavage development of zygotes are the egg nucleus and the yolk.
Explanation of Solution
Justification/explanation for the correct answer:
Option (d) states that the egg nucleus and the yolk are the major contributors to the cleavage patterns. The cleavage of the embryo occurs depending upon the amount of egg yolk present in the blastula (embryo after cleavage division is known as blastula). These cleavages can be holoblastic (total cleavage) or meroblastic cleavage (partial cleavage) that depends upon the amount of yolk present in the egg and the positioning of the nucleus in the egg. Hence, option (d) is correct.
The explanation for the incorrect answer:
Option (a) is given as sperm and egg cytoplasm. The cytoplasm is not the major contributing factor to the cleavage as the cleavage is mainly classified on the basis of the amount of yolk that is present in the egg. So, it is an incorrect option.
Option (b) is given as sperm and egg chromosomes. The chromosomes have nothing to do with the cleavage patterns. The chromosomes of the sperm and the egg consist of the genetic makeup of the embryo. So, it is an incorrect option.
Option (c) is given as ribosomes and mitochondria. These have an important role in the translation (expression of genetic material or formation of proteins) process and not in the cleavage divisions. So, it is an incorrect option.
Option (e) is given as pigments. Pigments can only be present after the genetic material expresses itself. The yolk and the egg nucleus contribute to the cleavage patterns of a zygote. So, it is an incorrect option.
Hence, options (a), (b), (c), and (e) are incorrect.
Therefore, it can be concluded that the cleavage patterns help in the organization and the development of different regions of the embryo or the blastula and turn it into a specialized region for the functioning of an organism. This depends on the amount of yolk present and the positioning of the nucleus in an egg and are thus, classified accordingly.
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Chapter 50 Solutions
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