Tag: the paths traversed by life

Hugo de Vries after his work on Evening Primose, put forth his theory explaining the structural changes in gene structures, called mutation as the cause of variations. Only large, single step and abrupt mutation termed as saltation are capable enough to drive the process of evolution.

• Mutations are the sudden changes that takes place in the DNA sequence of an organism causing structural changes in genes. 
  
• These are the permanent changes that can be either induced or occur naturally leading to the variation in the populations. Mutations is essential for speciation since variations are the raw material for evolution.
  

De Vries gave his mutation theory on organic evolution while working on Oenothera lamarckiana. Oenothera lamarckiana is an annual plant commonly called as evening primose. De Vries in his experiment observed that original plant showed some offsprings with different phenotypes. These mutations were passed from offsprings to their progeny. However, late it was observed that the variations were due to chromosomal segregations and not due to mutations.

• For a mutation to be evolutionary successful, it must occur in Germplasm DNA since germline mutations are the only one that can be passed on to offspring, when either a mutated sperm or oocyte come together to form a zygote.
  
• After this fertilization event occurs, germ cells divide rapidly to produce all of the cells in the body, causing this mutation to be present in every somatic and germline cell in the offspring; this is also known as a constitutional mutation.
  

Concept of mutations was put forth by Hugo de Vries who worked on evening Primose. He stated that mutation causes evolution and not the minor variations that were suggested by Darwin. Mutations are sudden, random and directionless while Darwinian variations are small and directional.

• The theory of mutation given by Hugo de Vries suggested that evolution is fueled by the occurrence of the discontinuous process called mutation, that arises in the genetic material suddenly and are transmitted to the next generation. 
• These mutations serve as raw material for evolution as they may provide a selective advantage to an individual. The selective advantage would allow an individual to reproduce successfully and hence, the natural selection would lead to evolution.

• Hooke's reputation in the history of biology largely rests on his book Micrographia, published in 1665. 
• Micrographia contains some physiological descriptions of Minute Bodies made by Magnifying Glasses with Observations and Inquiries through various lenses.
  
• On the Origin of Species (or, more completely, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life), published on 24 November 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology.
• Hugo Marie de Vries was a Dutch botanist and one of the first geneticists.
• He is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term "mutation", and for developing a mutation theory of evolution.
• A swan neck flask is a particular shape of plastic or glass tube leading into a test tube or other vessel.
• The "swan neck" significantly slows down the motion of air through the tube, and particles in the air, such as bacteria, become trapped on moisture on its inner surfaces. Louis Pasteur used  Swan-necked flask experiment for supporting the idea of the germ theory of disease.
• So, the correct answer is 'A- 4, B- 3, C- 1, D- 2'.

Recaptulation theory was modified in the light of evolution as biogentic law by a German biologists - Ernst Haeckel in 1968 AD. It states that ontogeny repeats phylogeny which means that an individual during its own development (ontogeny) passes through ancestral listor (Phylogeny).