According to science, there is a certain order and process in how we came into existence. Knowing the concept of Heredity and Evolution in Class 10 is crucial. It is for this reason that we are going to understand how heredity and evolution play a role in the life of human beings.
What is Heredity
The transmission of characters or traits from parents to their offspring (children) is termed as heredity.
Genetics is the study of heredity and other variations.
Those organisms that are identical copies of one another are termed as clones. They are exact carbon copies of each other.
Differences or variations occur in sexually reproducing characters. These discrepancies usually happen due to:
- Recombination of genes
- Crossing over
Important Related Facts
- Gregor Mendel was the first scientist who studied the inheritance of traits and he observed his results with a pea plant.
- The paired chromosomes are diploid while single, unpaired ones are haploid.
- The genetic materials that are present in all living organisms are DNA (Deoxyribose Nucleic Acid) and RNA (Ribose Nucleic Acid).
- Genotype is the composition of genes that are present inside an organism. Phenotype is the physical traits, those that are visible on the outside.
What forms the basis of heredity?
Mendel stated that heredity was controlled by particles. He termed these particles as germinal units or factors.
The Laws of Inheritance and Mendel’s work
Mendel stated the following Laws of Inheritance based on his observations:
- Law of Dominance
- Law of Segregation
- Law of Independent Assortment
He performed his experiments on the famous garden pea plant (Pisum sativum) and used quite a variety of characters such as:
- Tall/short plants
- Round/wrinkled seeds
- White/violet flowers
When two parents are crossed together to produce their progeny or offspring, this progeny belongs to the F1 generation, or also termed as the first filial generation. When this generation is crossed among themselves to produce the second generation of offspring, these plants are termed as the F2 or the second filial generation.
What happens during a monohybrid cross?
Monohybrid plants are these plants that have only one phenotype, that is, they may either tall or short, just to give an example.
Taking the above example into consideration, when all pea plants were bred with short pea plants, in the F1 generation, only tall plants were observed.
Now, if the F1 generation was crossed with each other, not all the plants are tall. Only three-quarters of the plants were tall while the remaining one-quarter was short.
What does this prove?
This proves that both the tall and short character was inherited in the F1 generation, but only the tallness phenotype was expressed due to it being the dominant gene.
What happens in a Dihybrid cross?
A dihybrid plant has two sets of contrasting characters; let us take an example of a plant with wrinkled and green seeds and a plant with rounded yellow seeds.
So in a dihybrid cross, the above example was crossed, which is, a plant with wrinkled green seeds was crossed with a plant with rounded yellow seeds.
In the F1 generation, only plants with rounded yellow seeds were observed.
On crossing the F1 generation with each other, certain other new combinations were observed. The resulting diagram explains the new combinations.
Image Credits: Google Images
The above observations were made based on calculations by the Punnett Square, which is easily understood in the diagram below.
Image Credits: Eweb Furman Edu
What is Evolution?
The series of slow and gradual changes which occur in primitive organisms over a long period of time (perhaps a million years) in which new species are formed.
Evidence of Evolution
- Homologous organs:
- Homology refers to those characteristics inherited by two organisms from a common ancestor
- Organs such as wings of a bat, wings of birds, flippers of seals, forelimb of a horse, and human arm have a universal fundamental anatomy that was present in their last common ancestors; as a result, their forelimbs are homologous organs.
- Man uses his hands to grab and perform tasks, whales use their flippers for swimming, bats and birds use their wings for flight and horses use their forelimbs for running.
- Analogous organs:
- Analogy refers to how two different organisms perform a similar function due to the evolution process and not common ancestry.
- An easy to understand example would be the wings of insects, bats, and birds that evolved autonomously in each family separately after diverging from an ancestor without wings. The wings of insects start off from the inner or outer surface of the insect’s body. Feathers of birds originate from their forelimbs, and the wings of bats start off from both the forelimb and the membranous skin of the abdomen.
Different theories of Evolution
- The scientist, Jean Baptiste Lamarck was the first to state the theory of evolution.
- But, it was Charles Darwin’s theory of evolution which became famous all around the globe. He explained his statement in his book titled ‘The Origin of Species’. This principle, proposed by him is commonly known as the Theory of Natural Selection by Charles Darwin.
- The main characteristics of his theory are:
- Limited space and food
- Struggles for existence
- Natural selection or more common, the survival of the fittest organisms
- Classification of evolution:
- Convergent evolution
- Divergent evolution
- Parallel evolution
- Stages of evolution:
Evolution is not a quick process, rather it takes place, little by little, very gradually over a long period of time, over several generations. An example is the evolution of feathers in birds due to the advantage of survival.
- Human evolution: although there were several races of human beings in the earlier times, they’ve all belonged to the species Homo sapiens.
When new species develop from the existing ones, it is termed as speciation.
Three major factors contribute to this phenomenon:
- Genetic drifting
- Geographical isolation
The dead remains of plant and animal organisms that lived in the remote past are termed as fossils. They are useful in determining the date and era in which the organism used to live in.
So, from Mendel’s pea plant to Darwin’s theory of evolution, this was a comprehensive study of heredity and evolution.
Do check out our article on A List of Short Humorous Stories for Class 10 here.