Heredity and Evolution class 10 notes

Heredity and Evolution :-

* The transfer of genetically based characters or traits from parents to their offspring is called heredity.

* Gregor Johann Mendel,

an Austrian Augustinian monk (1822–1884), performed the first ever scientific experimental study on heredity and is rightly called the Father of Genetics. He conducted   experiments on pea plants (Pisum sativum) and studied the inheritance of certain traits. 

* In 1944, Avery, MacLeod and McCarty proved that the chemical inherited is DNA, and it forms the chemical or molecular basis of heredity.

* Information about protein synthesis is stored in DNA, and synthesis of proteins is necessary for the body. These proteins are synthesised by DNA through RNA. This is called the Central Dogma.

* Transcription is the process of copying genetic information coded in DNA into the mRNA molecule.

* DNA itself cannot move to the site of protein synthesis to directly guide the process. Hence, it transfers its information to the single-stranded mRNA molecule.

* The transcribed RNA moves out of the nucleus to the ribosomes in the cytoplasm to direct protein synthesis.

* Dr Har Govind Khorana made an important contribution in the discovery of triplet codons for 20 amino acids.

* Translation is the process of polymerisation of amino acids to form a polypeptide chain.

* DNA acts as a repository of genetic information. The mRNA serves as a link between DNA and the polypeptide chain. As per the message on mRNA, amino acids are supplied by tRNA. Each tRNA has an anticodon having a complementary sequence to the codon on mRNA which is called translation.

* During this process, the ribosome keeps on moving from one end of mRNA to the other end by the distance of one triplet codon. This is called translocation .

* Sudden changes in the nucleotide in the gene cause a minor change called   mutation.

* Evolution

is the formation of more complex organisms from pre-existing simpler organisms over a 

period of time. It is a slow, progressive, natural and sequential development or transformation of 

animals and plants from ancestors of different forms and functions.

* Variation and heredity are the two basic factors of evolution. The selection of variants by the environmental factors forms the basis of evolutionary processes.

* Large amount of information has been collected for the last 200 years to support the theory of organic evolution. Such supporting information, which helps in accepting the theory, is called evidence. 

*

Morphological evidence of evolution reflects in the form of external features or the appearance of an organism.

* Anatomical evidence

of evolution is usually reflected in the form of structures, which appear similar in their organisation. The similarities found in different groups of organisms indicate that these organisms 

must have had a common ancestor.

* Different organisms have organs which perform similar function. These organs which have similar 

function but are different in structure and origin are called analogous organs, e.g. tail fin of a lobster 

and flukes of a whale, wings of a fly and wings of a bird and eyes of arthropods and eyes of 

vertebrates are all analogous organs. 

* Some organs are fundamentally same in structure and origin but are modified to perform different functions in different organisms. They are called homologous organs, e.g. forelimbs in humans are 

adapted for handling, while forelimbs of bat and bird are adapted for flying and those of whales and 

seals are adapted for swimming. 

* Organs that are found in reduced or rudimentary condition and do not perform any function in the 

possessor are called vestigial organs or non-functional organs, e.g. ear muscles, coccyx or reduced 

tail and plica semilunaris in man. 

* Fossils

are the preserved remains or traces of animals, plants and other organisms from the remote  past.

 The study of fossils is called Palaeontology,

which provides direct evidences in favour of organic  

evolution. It helps us to compare the past with the present so as to establish the changes that have 

occurred during evolution.

* The study of development of an organism from the stage of an embryo is called embryology.

The 

comparison of embryos states that in the course of development from the embryo to their adult form, 

animals go through stages that resemble or represent successive stages in the evolution of their 

remote ancestors. 

* According to Darwin’s theory of natural selection,

organisms produce more offspring than they 

need for their existence. They compete among themselves and fight with the environmental factors for 

their various needs in life. In the struggle for existence, those with favourable variations continue to 

exist and those with unfavourable variations die out. A new species is formed by natural selection.

* A species

is a population of organisms consisting of similar individuals that can breed together and 

produce fertile offspring.

* The process by which a new species develops from the existing species is known as speciation.

* Geographical isolation, genetic drift and natural selection are the important factors that contribute to 

speciation.

* According to Lamarck’s theory, variations that exist in an organism are transmitted to the next 

generation. These variations are called acquired characters, and Lamarck’s theory is called the theory 

of inheritance of acquired characters.

* Lamarck’s theory was rejected because acquired characters are not transmitted due to the genetic makeup of an organism. They cannot be transmitted to the offspring.

* Evolution of modern day man has been the greatest progress made in the history of evolution. Human evolution has been studied using various tools of tracing evolutionary relationships such as 

excavating, carbon-dating, studying fossils and determining DNA sequences.

* The three types of human ancestors are broadly classified as prior to ape man, ape man and early 

human.

A. Prior to Ape Man

1. Dryopithecus

* A group of apes whose fossils were found in India and has been named Sivapithecus.

* Their arms and legs were of almost equal length.

* They are supposed to be the common ancestors of ape and human.

2. Ramapithecus

* Earliest man-like fossil obtained from Africa and Asia about 10–15 million years ago.

* They could walk erect on the feet, had small canines and had a short face and small brain.

* By the molecular clock method, it was established that Ramapithecus was an ancestor to 

Orangutan.

B. Early Human

1. Homo neanderthalensis

* These early humans arose 1,00,000 years ago and flourished in Europe and Asia but became 

extinct about 25,000 years ago.

* They had a flat cranium, sloping forehead, protruding jaws, strong mandibles and no chin.

* They were intelligent, good hunters and used animal skin for clothing and buried the dead.

* They were contemporary to modern man and are considered cousins or uncles of modern man.

* They were wiped out by their more advanced cousins, the Cro-Magnon man about 25,000 years ago.

2. Homo sapiens fossilis (Cro-Magnon Man: Early Modern Man)

* Their fossils were discovered about 50,000 years ago from the caves of north-west Italy and rock 

shelter caves in France.

* The Cro-Magnon man was 1.8 metres tall with sturdy, less hair body and the cranial capacity was 

about 1650 cc.

* They had a large skull, high forehead, prominent chin and broad flat face.

* They were cave dwellers and hunters and had learnt drawing and painting pictures of 

contemporary animals.

                        modern man