Genetic Variation – Definition, Causes and Example

Genetic Variation

 Key Concepts

• Variation
• Heredity
• Acquired and inherited traits
• Darwin’s voyage
• Variation in finches
• Causes of variation
• Variation that favor survival
• Variations in plants

Introduction

Organisms belonging to similar species have same characters, but they also have different characters that makes them look different from each other. This is called a variation of traits.  

Traits are characters or features which decide how organisms look or behave. We all look like our parents, but we are not identical to them. We share similarities as well as differences with them.  

This is due to the phenomenon of heredity. 

Explanation

Heredity is the transfer of characters from parents to offspring. At the time of reproduction, the parents pass some of their features, or inherited traits to their offspring.  Examples of inherited traits in humans include height, eye color, dimples, freckles, and the shapes and sizes of fingers and toes. As we already know, when cells divide replication of DNA takes place; during this replication, genetic information is transferred. DNA contains information in the form of genetic codes, which are known as genes. Genes are also known as the unit of heredity. These genes are responsible for the appearance of characters or traits in an organism. 

Fig. No.1: Transfer of traits from parents to offspring. 

Individuals in a population do not look exactly the same. Every individual has a unique set of traits, such as size, height, color, body weight, skin color and even the ability to find food. 

Sometimes, offsprings of the same parents also show differences among themselves. You can find that among three siblings, one may be very tall, the other may have light hair, and the third may have a rounded nose tip. Such differences in individuals from the same parents are called variations. 

Variations are created at the time of sexual reproduction. During sexual reproduction, information from two parents are mixed, as a result variation is created. Whereas in asexual reproduction only one parent is involved, as a result, the entire genetic code is copied as it is. This results in organisms that are identical to their parents. 

Genetics is the study of heredity. However, not all traits come from heredity. Traits can be either inherited or acquired. For example, zebra finches can sing from an early age without even learning or practising. This is an inherited trait. In humans, attached earlobes or the ability to roll your tongue are examples of inherited traits. 

However, the song of the young finch changes as the bird gets older. After it hears other birds singing, its own songs become more complex. The ability to sing a more complex song is an acquired trait, a trait that is influenced by experience or the external environment. 

In humans, dancing or playing a sport can be examples of acquired traits. Acquired traits are not passed on by an organism to its offspring. 

Charles Darwin, a British naturalist, boarded the H.M.S. Beagle for a journey around the world on December 27, 1831. The ship reached the Galápagos Islands in the fall of 1835. Over there, Darwin made some important observations on different species, one of which was the finch.  

Darwin’s studies of these birds helped him recognize genetic variations in nature. In the Galapagos, the 13 species of finches that he saw were all similar in size, color, and habits. Only their beaks were different in size and had shapes ranging from very thick to very fine. In spite of these differences, Darwin thought the finches might all have come from one common ancestor. 

Darwin observed that each species of finch was very well adapted to its particular environment. 

For example, the different types of beaks enabled the finches to eat particular kinds of seeds, plants or insects. Each beak type was a variation of the same species. Such differences among members of the same species enable individuals to survive better and reproduce. Differences like these are caused by changes in an organism’s genetic makeup. 

Causes of variation : 

Variations are caused when an organism’s genetic composition is affected due to internal or external factors. Some of these causes are: 

1. Mutations: A mutation is a change in an organism’s DNA. Mutations are caused at the time of cell division or could be caused by environmental agents like heat. 

2. Error during replication: Changes in the genetic code can also occur because of an error in mitosis or meiosis. These types of changes can sometimes be lethal. 

3. Recombination: During sexual reproduction, genes recombine, which can lead to a new genetic code every time an offspring is produced. 

Variations for survival : 

We have learnt that all of Darwin’s finches on the Galápagos Islands can be traced back to a single species.  

How can we explain the variations among the beaks of these birds? 

We can assume that when the original species might have arrived at the Galápagos Islands, some of the birds might have become separated and flown off to the different islands of the Galapagos.  

On each island, different type of food was available. For example, if thick-shelled seeds were a main source of food on one island, birds with thick beaks would be the ones best suited to eat them. These types of birds would be the most likely to survive and reproduce there. Since this type of beak helps the survival and successful reproduction of that bird. Later, the entire population of birds on that island would have thick beaks.  

Now, considering insects as the major food source on another island, the birds having narrow grasping beaks would be more likely to survive and reproduce there. 

Darwin’s finches demonstrate how variations can favour certain animals over others.  

The beaks of the two populations of birds would remain different as long as the two finch species did not produce offspring with each other. Variations can help a species survive.  

This means that a variation can help individuals in a species live long enough to successfully reproduce. 

The trait will then be passed on to the next generation. 

What if a variation does not favor survival?  

If a variation does not favor the survival of an organism, then the individuals are less likely to reproduce and pass on the trait.  

Variation in plants: 

Several varieties of plants are well adapted to live in particular climates. Plants that grow in dry climates have very shallow roots that grow near the surface of the soil. This helps them to capture much of the rain that falls.  

Other plants have roots that extend deep into the ground.  

In both plants and animals, variations can help species in their struggle for existence by enabling individual organisms to survive and reproduce. 

Summary

• Organisms belonging to similar species have the same characters, but they also have different characters that makes them look different from each other.
• This is called a variation of traits.
• Traits are characters or features which decide how organisms look or behave.
• Heredity is the transfer of characters from parents to offspring.
• Traits that are passed on from parents to offspring during reproduction are inherited traits.
• Traits that an organism acquires in its lifetime through experience are called acquired
  traits. These traits cannot be inherited.
• Variations are caused by changes in an organism’s genetic makeup.
• Variations that help individuals in a species to survive and successfully reproduce are
  inherited, i.e., passed on to the next generation.
• Variations that do not favor the survival of the individuals are less likely to be inherited.
• In both plants and animals, variations can help species in their struggle for existence by
  enabling individual organisms to survive and reproduce.