Embryonic Development

In mammals, the developing embryo is connected with the placenta by umbilical cord.

An embryo is a multicellular diploid structure in its earliest stage of development, from the time of first cell division until birth. The internal cluster of cells forming the blastocyst later forms an embryo.

Conditional specification occurs when cell fate depends on interactions with neighboring cells, allowing for regulation if cells are removed. The fact that early removal has no effect, while later removal causes a defect, indicates that cells are not yet locked into a specific fate early on, which is characteristic of conditional specification.

The respiratory system, including the lungs and bronchial tree, is derived from the endoderm germ layer.

The standard stages of a frog life cycle are egg, tadpole, and adult. Larva is a term more commonly used for insects, not frogs.

Advanced anagen is the stage where the hair follicle is fully developed and reaches its maximum depth in the skin. Early anagen is the beginning of growth, while catagen and telogen are regression and resting phases.

During the catagen phase, the hair follicle shrinks and the base of the hair keratinizes to form a club hair as it detaches from the dermal papilla.

Monozygotic twins are those twins in which is zygote is fertilized by one sperm and during the cleavage, it gets divided into two separate zygotes. These type of twins are exactly identical.

Dizygotic twins may occur if two or more oocytes are released in one cycle. If each is fertilized, dizygotic twins may result. Fertility drugs are a common cause for dizygotic twins, but other factors, like family history, maternal age or weight, can also lead to dizygotic twinning. Thus, the correct answer is option D.

All epithelia are separated from their underlying tissues by an extracellular basement membrane which is fibrous in nature. The basement membrane is the fusion of two lamina namely, the basal lamina and the reticular lamina. The lamina reticularis is attached to the basal lamina with collagen anchoring fibrils and fibrillin microfibrils. The two layers together are collectively referred to as the basement membrane.

Blastula differentiate into various regions and cells (blastomeres) of a particular region form a particular part of adult body, hence these areas are called presumptive areas and at this stage if cells of a particular area removed the adult lacks a particular part from its body.

In microlecithal eggs or alecithal eggs, the cleavage results in the production of closely packed blastomeres. The stage in which solid mass of blastomeres appears is said to be morula, whereas blastula is hollow with a cavity known as blastocoel.

Hematopoiesis is the formation of blood cellular components. In developing embryo, blood formation occurs in aggregates of blood cells in the yolk sac called, blood islands. As development progresses, blood formation occurs in the spleen, lymph nodes, and liver. 

In Intra-Uterine Transfer (IUT) embryo with more than 8-blastomeres stage (morula) is used for transfer into the uterus after induced fertilisation in the laboaratory.