Print

10.8Problems

 

 

The embryo of triploblastic organisms consists of three basic structures. Name these structures and the organs and tissues that develop from them.

 

 

Using fruit flies and frogs as examples, explain how the anteroposterior axis of animals is determined in the early stages of development.

 

Explain the concept of induction using examples.

 

 

Using the ABC model, explain how double flowers are formed. Also outline which organs in a normal flower form which organs in these cases.

 

 

The embryo of triploblastic organisms consists of three basic structures. Name these structures and the organs and tissues that develop from them.

The embryo of triploblastic organisms consists of three basic structures: the ectoderm, the mesoderm and the endoderm. The cells in these germ layers that are roughly formed during the early stages of development are eventually differentiated into the following tissues and organs:
Ectodermal origin: epidermis and central nervous system (skin, brain, etc.)
Endodermal origin: digestive organs and respiratory organs (liver, pancreas, stomach, intestines, lungs, etc.)
Mesodermal origin: muscle tissues and connective tissues (skeletal muscles, heart, blood, kidneys, etc.)

 

 

Using fruit flies and frogs as examples, explain how the anteroposterior axis of animals is determined in the early stages of development.

The mechanism behind the determination of the direction (axis) of animals during the early stages of development varies by species. In fruit flies, the anteroposterior axis is determined prior to the initiation of development by the action of maternal factors - nanos and bicoids - unevenly stored in the unfertilized egg. In frogs, the unfertilized egg already has an axis that connects the animal pole with the vegetal pole; upon fertilization, the maternal factors stored near the vegetal pole of the ovum move approximately 60 - 90 degrees in a particular direction with the surface part of the ovum, thereby determining the dorsoventral axis. The side opposite the sperm entry point becomes the future dorsal side. As cleavage proceeds, and when gastrulation occurs (in which the cells located on the dorsal side move inward), the fore-invaginated part becomes the anterior side and the rear-invaginated part becomes the posterior side, thus determining the anteroposterior axis.

 

Explain the concept of induction using examples.

Induction is a phenomenon that determines the destiny of adjacent cells and tissues through its action on them. As an example, in neural induction, the ectoderm undergoes induction caused by secretory substances mainly supplied by the mesoderm in the inside and tail parts of the embryo, creating a neural tube that later becomes the brain and the spinal cord.

 

 

Using the ABC model, explain how double flowers are formed. Also outline which organs in a normal flower form which organs in these cases.

Taking the simplest form of double flower as an example, if the expression of gene group C is lost, both the first and second whirls become petals (Column Fig. 10-4E). In this case, stamens and carpels become petals and calyxes, respectively. In the case of flowers in which calyxes appear as petals, even if the expression of gene groups B and C is lost and only gene group A is expressed in all whirls, the flowers appear as double flowers.

Top of Page

next

prev