Mammals like us have single row of teeth while Sharks have many!!!!

Read on to know ..........WHY?

As we know that all the information about an individual living organism is the information contained in its genes. Gene expression is a process of converting this genetic information into proteins that make body's structures and carry out its vital processes.

Although teeth usually do not become visible until after birth, their formation starts early in development. Teeth develop from the epithelium and mesenchyme, two key tissue layers within the mammalian embryo. The first sign of tooth development in mammals is the thickening of the epithelium along the jaw line to form a band of cells called the dental lamina. Researchers confirmed that it was indeed the mesenchyme that carried tooth initiation signals later in development, but how those signals were restricted to the area beneath the tooth row was unknown. Past studies had shown bone morphogenic protein 4 (BMP4) to be an important factor for the initiation of teeth, and that a protein called Msx1 amplifies the BMP4 tooth-generating signal.

A recent study published in Journal Science provides the first solid proof that the precise space where mammals can develop teeth (called the "tooth morphogenetic field") is shaped and restricted by the effect of Oddskipped related-2 (Osr2) gene on the expression of the Bmp4 gene within the mesenchymal cell layer. Osr2 gene is present in high amounts towards the tongue side of the jaw and decreases towards cheek. Since the presence of Osr2 restricts the teeth forming effect of BMP4 gene, so teeth will be formed at a place with low concentration of Osr2 (high concentration of BMP4). So Osr2 restricts Bmp4 expression to the tooth mesenchyme under the dental lamina only, due to which teeth grow only in the region of dental lamina.

These results suggest that diversity in the number of tooth rows across species may be due to evolutionary changes in the control of the BMP4/Msx1 pathway. In mammals, Osr2 suppresses this pathway to restrict teeth within a single row.

Question of the Week

Biobasics Question of the Week:

What is Adaptive Radiation?

Biobasics Solution

Adaptive radiation is a process of evolution starting from a single point diversifying rapidly into different morphological adaptations. Phenotypes adapt in response to the environment, with new and useful traits arising. There are two basic causes of adaptive radiation: Innovation and Opportunity. (Source: en.wikipedia.org)

Innovation: The evolution of a novel feature may permit a clade to diversify by making new areas of morphospace accessible. A classic example is the evolution of a fourth cusp in the mammalian tooth. This trait permits a vast increase in the range of foodstuffs which can be utilized, with species able to specialize on feeding on a range of foodstuffs.

Opportunity: Adaptive radiations often occur as a result of an organism arising in an environment with unoccupied niches, such as a newly formed lake or isolated island chain. The colonizing population may diversify rapidly to take advantage of all possible niches.

Darwin's Finches are one of the best examples of Adaptive Radiation.
Adaptive radiations commonly follow mass extinctions: an extinction, many niches are left vacant. A classic example of this is the replacement of the non-avian dinosaurs with mammals at the end of the Cretaceous, and of Brachiopods by bivalves at the Permo-Triassic boundry.

Hide and Seek: Can you spot me??

The picture shows a classical example of camouflage by a desert adder in order to hide from its predators and find a prey by burying itself in the sand. Desert adder is a venomous viper species found in Namibia and southern Angola. Here only the head and camouflaged eyes of the reptile can be seen. (Source: Incredible Creatures by The Nature Academies).

Question of the Week

Biobasics Question of the Week:

Which of the nucleic acids –DNA or RNA - is susceptible to alkaline hydrolysis? Why?

Biobasics Solution:

RNA is susceptible to alkaline hydrolysis because of the presence of 2´ hydroxyl group in Ribose sugar of RNA. In contrast, DNA has deoxyribose sugar which contains -H atom at 2´ position instead of –OH of ribose, hence rendering the DNA molecule resistant to alkaline hydrolysis. (Note that both the Nucleic acids are susceptible to acidic hydrolysis).