Category Zoology

Why don’t identical twins have identical fingerprints?

Fingerprint formation is like the growth of capillaries and blood vessels in angiogenesis. The pattern is not strictly determined by the genetic code but by small variables in growth factor concentrations and hormones within the tissue. There are so many variables during fingerprint formation that it would be impossible for two to be alike. However it is not totally random, perhaps having more in common with a chaotic system than a random system.

It is believed that the development of a unique fingerprint ultimately results from a combination of gene-environment interactions. One of the environmental factors is the so-called intrauterine forces such as the flow of amniotic fluid around the fetus. Because identical twins are situated in different parts of the womb during development (although they are not static), each fetus encounters slightly different intrauterine forces from their sibling, and so a unique fingerprint is born.

            Your genes specify only your biochemistry and through it, your general body plan. The pattern of your fingerprints forms rather in the way that wrinkles form over cooling custard. At most you may predict, say, the fineness of the wrinkles and their general pattern. Fingerprints are just one example. Many of your features could mark you out from any clone. Your genome only controls gross characteristics such as the rates at which the skin and its underlying attachments develop and grow. Even if there is no way for genes to specify everything exactly, there is no way the genome could carry enough information for the details. If our genomes had to specify everything, we would not be here. But, while the consequences of imperfect specification are usually trivial, they may have more serious effects. A minor distortion of a blood vessel could give poor blood flow or an aneurysm, and the branching and interconnection of brain cells affect mental aptitudes. That is why, though bright parents tend to have bright children, dimmer ones may have a child genius and vice versa.

How do turtles reproduce?

The turtle lives ‘twixt’ plated decks

Which practically conceal its sex?

I think it’s clever of the turtle

In such a fix to be so fertile

            The poet Ogden Nash was right about the turtle’s external ambiguity and fertility, according to Grzimek’s Animal Encyclopedia (Van No strand Reinhold). Turtles are not only enthusiastic breeders; they also have external sexual characteristics that often make it hard for creatures other than turtles to determine which is which. The male is sometimes distinguishable by an indentation or curvature in its plastron, or lower shell, which fits over the back of the female; females have a flat or convex plastron.

To fertilize female’s eggs, the male turtle conceals a sexual organ inside the cloaca, or waste removal chamber. The male positions itself over the female and often grasps the upper shell, or carapace, with its claws, then curves its tail until the vent contacts the female’s vent; the penis emerges for often fertilization. The often dozens of eggs develop internally and are then usually laid and buried in sandy soil.

Fertilization is sometimes preceded by elaborate courtship rituals, with hours of demonstration followed by a few minutes of copulation. The female can store sperm to fertilize its eggs, sometimes years later. 

How do spiders manage without getting caught in their own web?

A thin coating of oil on the surface of the spider’s legs prevents them from sticking to their own web.

Spiders have 3 pairs of spinnerets (silk spinning apparatus) located beneath the hind tip of their abdomen. Silk, made up of proteins, secreted by the silk glands, and are made into fibres as thin as a thousandth of a millimetre. The threads we see are actually a bundle of these fibres. The proteins are water soluble when secreted, but when made into a fibre, some Physical and chemical changes take place, and so, after a while the fibre becomes tough and does not dissolve in water. In fact, it becomes stronger than a steel wire of the same thickness. Hence, the spider silk is also used to make bullet proof vests.

To construct a web, the spider first lays the radical threads. These resemble the spokes on a wheel and they radiate from the centre or hub of the web. The radial fibres are then connected by spiraling threads. There may be 10-60 turns in a web. To capture the insects, spiders scatter small glue droplets throughout. The glue droplets remain sticky by absorbing moisture from the air. They also increase the capacity of the web to resist wind forces.

While some spiders do not place glue droplets around the central area of their web so that they can wait there for the prey, a few others attach a separate ‘signal thread’ from the web’s centre to a nearby place (not on the web) where it can conveniently relax. When the insects get stuck to web, spiders sense the vibrations and leap on the prey.

To help avoid being caught in their own webs, the spiders secrete oil and coat it on their toes. One can test this by dipping a spider’s legs in ether, an organic solvent, which dissolves the oil. If the spider is returned to the web after the dip, it will be caught in its own web.

Why is the sting of a scorpion more painful than that of a snake sting? What are the chemicals in their poisons?

Scorpion’s venom acts on the nerve tips and roots whereas snake’s poison acts on dendrites and axons of the nerves. As defence and prey capture are the sole aim of these and other animals and insects, it is the purpose on hand that determines venom’s composition and type.

 Cobra venom consists of 10 different enzymes, several different types of neurotoxins, cardio-toxins, cytotoxins, dendrotoxins and fasciculins (for example, lysocephalins, lysolecithins which are phospholipids). Snakes of the elapidae family (for example cobras, kraits and mambas) have venoms that kill primarily through neuro-muscular paralysis. It contains 60-75 amino acids and target nicotinic cholinoceptors in the muscle cell membranes which are sensitive to a chemical transmitter, acetylcholine. (Acetylcholine is released from nerve endings in response to an electrical impulse in the nerves.) The amino acids in snake’s venom block the junction between the nerves and the muscle. Scorpion’s venom consists of an arsenal of toxic compounds which contain 37 amino acids called charybdotoxin.

            When a scorpion stings these acids incapacitate the nerve cells causing severe pain, by rigidly binding with sulphur bonds unlike the snake’s toxin which binds by a ligand series. Moreover snake’s venom is digestible, but scorpion’s venom is not          

Why do snakes move in a zigzag manner?

The snakes are the only vertebrates which have efficiently overcome the handicap of absence of limbs making them survive with relatively long, slender body and a cosmopolitan habitat bestowed on them by nature. This achievement was basically by adapting different modes of locomotion fulfilling the need of the environment (terrestrial, water and arboreal) in which the animals lives.

The most common mode of progression which is generally employed by all species and is characteristic to them is the ‘serpentine type of locomotion’ better named as ‘undulatory motion’ in which the animal forms a zigzag track.

The basic necessity and attribute of this motion is some form of maximum provided by any projections or depressions on the substratum like rocks, branches, twigs, dust, sand or pebbles. This roughness in real sense resists the long, slender body to move on a straight line owing to which the body assumes a position of a series of s-shaped horizontal loops or curves.

 Each loop or curve which faces some resistance in turn delivers an equal and opposite thrust against the resistance leading to the formation of a series of  lateral or horizontal waves produced by a flow of muscular  contraction and relaxation passing from head to tail, resulting in the , propulsion of the  body in the forward direction.

 This kind of a zigzag motion is undergone only when the surface is rough enough to offer maximum resistance. It is of no use when they move on a really smooth surface, where they are offered least resistance. 

 

Why does the light of firefly twinkle while that of glow-worm remains constant?

            Fireflies are not really flies and glow worms are not really worms. Fireflies are soft bodied beetles in the family of Lampyridae and glow worms are actually young fireflies (larvae).

            Although the luminescent molecule in many organisms is yet undetermined, in most organisms the light producing reaction is mediate by the action of a class of enzymes called luciferases on their substrate called luciferins.

            Some organisms do not make use of luciferases but instead use calcium activated photo proteins in their bioluminescent reaction involves the oxidative decarboxylation of luciferins in the site of special cells called photocytes present on their lower abdomen segments to attract mates. It appears that male fireflies flashing patterns are mating signals and females seem to prefer the most rapidly flashing males.

            Since glow worms do not mate, no one knows exactly why they glow. But glow worms are carnivorous and probably use the light to lure or locate its prey.

            There are over 2000 species of fireflies inhabiting the tropical and temperate regions. Fireflies of the same species recognize each other by number of flashes used the frequency of flashes and colour of the light. Fireflies’ eggs are also reported to glow.