Which of the following is common to the development of both birds and mammals? a. holoblastic cleavage b. epiblast and hypoblast c. trophoblast d. gray crescent

Verified step by step guidance

1. Identify the terms: Holoblastic cleavage refers to a type of cleavage pattern where the entire egg is evenly divided into smaller cells. Epiblast and hypoblast are layers formed during the early development in the embryo. Trophoblast is the outer layer of cells in the blastocyst which provides nutrients to the embryo and develops into a large part of the placenta. Gray crescent is an area in amphibian eggs that appears after fertilization, important for the development of the dorsal side of the embryo.
2. Understand the development in birds and mammals: Birds and mammals both develop from embryos that form layers known as the epiblast and hypoblast. These layers are crucial as they contribute to the formation of different tissues and organs in the developing embryo.
3. Analyze the options: Holoblastic cleavage is typical in birds but not in mammals, as mammals (especially placental mammals) undergo meroblastic cleavage due to the presence of a large amount of yolk. The gray crescent is specific to amphibians and is not involved in bird or mammal development.
4. Evaluate the relevance of trophoblast: While trophoblast is a critical component of mammalian development, forming part of the placenta, it is not a feature in avian development, as birds lay eggs and their embryonic development occurs outside the mother's body.
5. Conclude the correct answer: The correct answer is 'b. epiblast and hypoblast' because these layers are common to the early embryonic development in both birds and mammals.

Key Concepts

Embryonic Development

Embryonic development refers to the series of stages that an embryo undergoes from fertilization to the formation of a fully developed organism. In birds and mammals, this process includes specific cleavage patterns and the formation of germ layers, which are crucial for the differentiation of tissues and organs.

Germ Layers

Germ layers are the primary layers of cells in the early embryo that give rise to all tissues and organs. In both birds and mammals, the epiblast and hypoblast are two key layers formed during development, with the epiblast contributing to the embryo and the hypoblast playing a role in supporting structures.

Cleavage Patterns

Cleavage patterns refer to the way in which a fertilized egg divides to form an embryo. Holoblastic cleavage, which is complete division of the egg, is common in mammals, while birds exhibit a modified form due to their larger yolk. Understanding these patterns is essential for comparing developmental processes across species.