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Basis of Genetic Inheritance

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A summary of all the constituents of genetic inheritance & the trinity of Molecular Genetics.

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Physical and Chemical Basis of Heredity

Physical Basis: Gregor Johann Mendel introduced in the year 1866 that

particles termed as germinal units or factors controlled heredity. These were existed in both the somatic cells and also the germinal cells. Although he was not capable to really see these particles, he did elucidate the pattern of inheritance of genetic characters. It was the gamete that carried such factors to the next generation and therefore gametes form the physical basis of the heredity.

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Physical and Chemical Basis of Heredity

Chemical Basis:Now it is recognized that genes control heredity

and these are exact segments of chromosomes and therefore are particulate bodies.

The genes travel from one generation to the other carrying the traits and as gene is comprisedof DNA and protein, the DNA portion functions as the chemical basis of the heredity.

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Experiments of Gregor Mendel & subsequent work led to a clear understanding genetics.

Chromosomal theory of inheritance : Inherited traits are controlled by the genes

that reside in the chromosome, which are faithfully transmitted through gametes to future generation

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What does Genetics mean?

“It is the branch of biology concerned with hereidty & variation.”

Involves the study of cells, individual, their offsprings and the populations within which populations live.

Geneticists investigate all forms of inherited variations as well as the molecular basis underlying such characteristics.

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What is the center of heredity in a cell?

In eukaryotes nucleus contains the genetic information in the form of genes on chromosomes.

In prokaryotes such as bacteria the genetic materialexists in an unenclosed but recognizable area of the cell called nuclear region.In viruses the genetic material is ensheathed in a protein coat, together constituting the viral head or capsid.

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What is a gene?

“Functional unit of heredity residing at a specific point along a chromosome”.Conceptually it is an informational storageunit capable of undergoing replication, expression & mutation.Is a very complex element.Biochemically, a gene is a lengthof DNA that specifies a product or action.

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What is a chromosome?

In virus & bacteria, which have a single chromosome, it is most simply thought of as a long, usually circular DNA molecule organized into genes.

Most eukaryotes have many chromosomes, that are composed of linear DNA molecule intimately associated with proteins.

Eukaryotic chromosomes contain many nongenic regions.

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What & how can chromosomes be visualized?

If chromosomes are released from viral head or bacterial cell they can be visualized under electron microscope.

In eukaryotes chromosomes are most easily visualized under light microscope when they are undergoing mitosis or meiosis.

As in division process the chromosome is tightly coiled & condensed.

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How many chromosomes does an organism have?

Although there are exceptions but, numbers of most eukaryotic species have a specific number of chromosomes called the diploid number (2n) in each somatic cell.

Example: Humans have a diploid number of 46 chromosomes, which are found to

occur in pairs each member of which shares a nearly identical appearance when visible during cell division. Called Homologus chromosomes, the members of each pair are identical in their length & in the location of centomere, the point of spindle fiber attachment during division.

They also contain the same sequence of gene sites, or loci, and pair with one another during gamete formation.

The number of different types of chromosomes in any diploid species is equal to half the diploid number and is called the haploid number (n).

Yeast are haploid during most of their life cycle & contain only one set of chromosomes.

Many plant species are sometimes characterized by more than two sets of chromosomes and are said to be polyploid.

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What is accomplished during the process of mitosis & meiosis?

Mitosis is the process by which the genetic material of eukaryotic cells is duplicated & distributed during cell division.

Meiosis is the process whereby cell division produces gametes in animals & spores in most plants, which serves as basis for transmission of genetic information between generations.

Mitosis occur in somatic tissue & yields two progeny cells with an amount of genetic material identical to that of progenitor cell, meiosis creates cells with precisely one half of the genetic material.

Each gamete receives one member of each homologous pair of chromosomes & is haploid.

This reduction in chromosome number is essential if the offspring arising from two gametes are to maintain a constant number of chromosomes characteristic of their parents and other members of species.

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Nucleic acids & Proteins serve as the molecular basis of genetics?

Trinity Of Molecular Genetics: Includes DNA, RNA & proteins DNA serves as the genetic material in all living organisms as well as

in most viruses. DNA is organized into genes & store genetic information. As part of the chromosomes, the information contained in genes can

be transmitted faithfully by parents through gametes to their offsprings.

Genetic information in DNA in most cases is first transferred to a closely related nucleic acid, RNA.

In eukaryotic organisms, RNA most often carries the genetic information out of the nucleus, where chromosome reside, in the cytoplasm of the cell.

Information in RNA is translated into proteins(end product of most all genes).

DNA makes RNA, which makes protein.

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Tamarin, R.H.2009. PRINCIPLES OF GENETICS(with cd). Tata McGraw Hill Publishing Co, New Delhi, India.

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