A change in the amount of yolk and its distribution in the egg will affect:

Explanation

Note: Cleavage is a series of cell divisions by which a single fertilized egg cell is transformed into a multicellular body, the blastula. Characteristically no growth occurs during cleavage, the shape of the embryo is unchanged except for the formation of central cavity (the blastocoel), and the ratio of nuclear material (DNA) to cytoplasm increases. The mode of cleavage is determined by the amount of yolk and its distribution. On this basis cleavage may be holoblastic and meroblastic. The correct option is: a) Pattern of cleavage. Explanation of each option: a) Pattern of cleavage: Cleavage is the rapid series of cell divisions that occur in the zygote (fertilized egg) after fertilization. The amount of yolk and its distribution in the egg can significantly influence the pattern of cleavage. In eggs with a moderate or even distribution of yolk, the cleavage is typically holoblastic, meaning the entire egg is divided into smaller blastomeres during each cell division. Examples of animals with eggs showing holoblastic cleavage include sea urchins and frogs. In contrast, eggs with a large amount of yolk that is concentrated at one end (telolecithal eggs) may undergo meroblastic cleavage. In meroblastic cleavage, only a portion of the egg with little yolk (the animal pole) undergoes division, while the yolk-rich portion (the vegetal pole) does not divide. Birds and reptiles are examples of animals with eggs showing meroblastic cleavage. b) Number of blastomeres produced: The number of blastomeres produced during cleavage is not directly affected by the amount of yolk or its distribution in the egg. Instead, the number of blastomeres is determined by the number of cell divisions that occur during cleavage. In both holoblastic and meroblastic cleavage, the number of blastomeres increases as cleavage progresses. c) Fertilization: The process of fertilization itself is not affected by the amount of yolk in the egg. Fertilization involves the fusion of sperm and egg to form a zygote, regardless of the yolk content. d) Formation of zygote: The formation of the zygote occurs through fertilization, which is the fusion of the sperm and egg nuclei. The presence or distribution of yolk in the egg does not affect the formation of the zygote during fertilization. In summary, the correct option is (a) Pattern of cleavage. A change in the amount of yolk and its distribution in the egg can significantly influence the pattern of cleavage, resulting in either holoblastic or meroblastic cleavage, which determines how the zygote divides and develops into an embryo.