Comparative anatomy and morphology NEET



Vestigial organs: 
  • Human body- canine, tail bone (coccyx), wisdom teeth (last one pair), body hair, third eyelid (nictitating membrane)
Atavism: A tendency to revert to something ancient or ancestral.
  • Hind limbs in cetaceans (aquatic mammals).
  • Extra toes of the modern horse.
  • Reappearance of limbs in limbless vertebrates.
  • Re-evolution of sexuality from parthenogenesis in orbitid mites.
  • Teeth in chickens.
  • Dewclaws in dogs.
  • Reappearance of prothoracic wings in insects.
  • Reappearance of wings on wingless stick insects and earwigs.
  • Atavistic muscles in several birds and mammals such as the beagle and the jerboa
  • Webbed feet in adult axolotls.
  • Human tails (not pseudo-tails) and supernumerary nipples in humans (and other primates).
  • Color blindness in humans
Comparative anatomy and morphology
Homologous organs
Analogous organs
Homology indicates common ancestry.

Homology is based on divergent evolution.

For example whales, bats, Cheetah and human (all mammals) share similarities in the pattern of bones of forelimbs

Though these forelimbs perform different functions in these animals, they have similar anatomical structure –

all of them have humerus, radius, ulna, carpals, metacarpals and phalanges in their forelimbs.

Hence, in these animals, the same structure developed along different directions due to adaptations to different needs.

This is divergent evolution and these structures are homologous.

Other examples are vertebrate hearts or brains.

In plants also, the thorn (protection) and tendrils (support) of Bougainvillea and Cucurbita represent homology
      
        Differentiate between Homologous and Analogous Organs , with ...
One can say that it is the similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function

Analogy  is based on convergent evolution

Wings of butterfly and of birds look alike. They are not anatomically similar structures though they perform similar functions.

Sweet potato (root modification) and potato (stem modification) for storage of food is another example for analogy.

Hence, analogous structures are a result of convergent evolution - different structures evolving for the same function and hence having similarity.

Other examples of analogy are the eye of the octopus (invaginations of the body surface) and of mammals (outgrowths of the brain)

sting of scorpion (last abdominal segment) and honey bee (ovipositor)

tendrils of passiflora (stem modification) and pisum sativum (leaf)



The flippers of Penguins (Bird) and Dolphins (mammal).


      Convergent Evolution of Wings | Convergent evolution, Childrens ...
      

Comments

Post a Comment

Popular posts from this blog

6.10 DNA FINGERPRINTING

Image
  6.10 DNA FINGERPRINTING   DNA fingerprinting is a very quick way to compare the DNA sequences of any two individuals. DNA fingerprinting involves identifying differences in some specific regions in DNA sequence called as repetitive DNA, because in these sequences, a small stretch of DNA (TANDEM REPEATS) is repeated many times.  Satellite DNA Repetitive DNA are separated from bulk genomic DNA as different peaks during density gradient centrifugation.  The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Depending on base composition (A : T rich or G:C rich), length of segment, and number of repetitive units, the satellite DNA is classified into many categories, such as micro-satellites, mini-satellites etc.                                 POLYMORPHISM  &  POLYMORPHIC DNA  Polymorphism is a variation at genetic...
Read more

DIGESTION AND ABSORPTION

Image
DIGESTION AND ABSORPTION Food is one of the basic requirements of all living organisms.  The major components of our food are carbohydrates, proteins and fats.  Vitamins and minerals are also required in small quantities.  Food provides energy and organic materials for growth and repair of tissues.  The water we take in, plays an important role in metabolic processes and also prevents dehydration of the body.  Biomacromolecules in food cannot be utilised by our body in their original form. They have to be broken down and converted into simple substances in the digestive system.  This process of conversion of complex food substances to simple absorbable forms is called digestion and is carried out by our digestive system by mechanical and biochemical methods.  General organisation of the human digestive system is shown in Figure 16.1. 16.1 DIGESTIVE SYSTEM  The human digestive system consists of the alimentary canal and the a...
Read more

Regulation of Breathing

Image
  Regulation of Breathing The regulation of breathing is based in the body's acid/base balance. The Central Chemoreceptors (CCR), primarily responsible for the breathing stimulation, are affected by the PaCO 2.  The responsiveness of the peripheral receptors is tied to the level of pH and PaCO 2 . Together these provide the ultimate in servo-control - sensors provide feedback that increase or decrease breathing. Medullary Respiratory Center The rhythmic cycle of breathing originates in the medulla. Higher brain centers (voluntary control), systemic receptors, and reflexes modify the medulla's output. However, no truly separate inspiratory and expiratory centers have been identified. The medulla does contain several widely dispersed groups of respiratory-related neurons that form dorsal and ventral respiratory groups. Fig-Schematic illustration of the respiratory components of the lower brainstem (pons and medulla oblongata). PNC = pneumotaxic center; APC = apneustic center; DR...
Read more