important points of heredity and evolution
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Answer:
The study of heredity and variation is known as genetics. Heredity is defined as transmission of characteristics from parents to offspring’s. The differences in characters of parents and offspring’s is known as variation.
There are two types of variation- somatic variation and gametic variation.
Somatic variation occurs in the somatic cell of the body. They are not inherited or transmitted in the next generation. So, they are also known as acquired traits.
Gametic variation occurs in the germ cells of the body. They are inherited in the next generation. So, they are known as inherited traits. (NTSE)
Importance of variations
It is the basis of the heredity.
It is the basis of the evolution also.
It increases the chances of the survival of the organism according to the changing environment.
Causes of variation
The most common causes of variations are mutation, recombination and random mating. Recombination or crossing over is one of the important reason for variation. It is a exchange of chromosome segment at the time of gamete formation.
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The study of heredity and variation is known as genetics. Heredity is defined as transmission of characteristics from parents to offspring’s. The differences in characters of parents and offspring’s is known as variation.
There are two types of variation- somatic variation and gametic variation.
Somatic variation occurs in the somatic cell of the body. They are not inherited or transmitted in the next generation. So, they are also known as acquired traits.
Gametic variation occurs in the germ cells of the body. They are inherited in the next generation. So, they are known as inherited traits. (NTSE)
Importance of variations
It is the basis of the heredity.
It is the basis of the evolution also.
It increases the chances of the survival of the organism according to the changing environment.
Causes of variation
The most common causes of variations are mutation, recombination and random mating. Recombination or crossing over is one of the important reason for variation. It is a exchange of chromosome segment at the time of gamete formation.
Mendel and his contribution in Genetics
G.J. Mendel started his work on Pisum sativum (garden pea). He was known as Father of genetics. He had chosen seven pair of contrasting character-
The reason of choosing garden pea for experiment was-
Short life cycle
Large number of seeds produced
Self-pollination
Mendel Laws
Law of Dominance: If the two alleles at a locus differ, then one, the dominant allele, determines the organism’s appearance; the other, the recessive allele, has no noticeable effect on the organism’s appearance.
Law of Segregation: The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes.
Law of Independent Assortment: Each pair of alleles segregates independently of other pairs of alleles during gamete formation
Monohybrid Cross
When one pair of contrasting characters was taken to cross two pea plants, it is known as monohybrid cross.
dyhybrid cross
When two pairs of contrasting characters are taken to cross two plants, it is known as dihybrid cross.
Sex Determination
Sex determination is used to defined the sex of the offspring’s. Environment and genetic factors determine the sex of the offspring’s. Environment factor includes temperature such as gender in turtles are determined according to the temperature.
Types of Sex Determination
Different types of sex determination are- XX-XY type (humans), XX-XO type (insects), ZW-ZZ type (chicken) and ZO-ZZ type (moths and butterflies).
Genetic factors include the presence of sex chromosomes. For example, in humans, presence of two X chromosomes leads to female offspring whereas presence of one X and one Y chromosome forms male offspring’s.
In human beings there are 23 pairs of chromosomes. Out of these 22 pair of chromosomes are known as autosomes whereas 23rd pair of chromosomes are known as sex chromosomes or allosomes. Sex of the offspring’s is determined by the chromosome inherited from the father.
Evolution
The sequence of gradual changes that takes place in an organism over a million of years and leads to the formation of new species is known as evolution.
J.B. Lamarck was the first scientist who gave the theory on evolution. He gave the theory of inheritance of acquired characters. Later on, Charles Darwin came and gave the theory of natural selection or Darwinism. According to his theory, evolution occurs through natural selection.
1. Theory of Lamarckism
This theory is also known as “Theory of inheritance of acquired characters”. Lamarckism is based on the following postulates-
Living organism tends to increase in size.
New needs lead to the formation of new organs.
Continued use of a particular organ makes it more developed and disuse of an organ leads to its degeneration.
New characters are acquired by individuals during their lifetime
2. Theory of Darwin
Darwin theory was also known as “Theory of Natural selection”.
Postulates of Darwin theory
Speciation (formation of species) - Useful variations from generation to generation gives rise to the formation of new species.
Struggle of the existence Due to multiplication of organisms and limited food and space, there exists competition among the organisms.
Survival of the fittest or Natural selection Nature selects those characteristics or organisms that are useful and are best adapted to the prevailing conditions. “For example: Industrial melanism observed in peppered moth in Britain”
Speciation
Origin of new species from already existing species is known as speciation. Speciation can take place through-
Gene flow can lead to speciation. It is a transfer of genetic variation from one population to another
Random change in allele frequency known as genetic drift can also leads to speciation.
Natural selection is another reason through which speciation can take place
Geographical barriers such as mountains, rivers can also lead to speciation. This is known as geographical isolation.