Inheritance,inheritance definition biology.

INHERITANCE

 Gene is the fundamental unit of heredity.

Define the following?

 Genetics:

     It is the branch of biology in which we study the transmission of characters from parent to offspring.

Heredity:

     The characters which are transferred from parent to offspring is called heredity.

Variation:

      The differences in individuals of the same species is called variation.

Gene:

      It is a chemical substance present on chromosome. It Consists of two Alleles. Gene controls specific characters.

Allele:

     Alternate form of gene in a gene pair is called Allele.

Homozygous:

      An individual is said to be homozygous if two members of the gene pair controlling a given character are identical, e.g. XX.

Heterozygous:

     An individual is Said to be heterozygous if two member of a gene pair controlling a given character are different.

Genotype:

     The genetic make up of an organism. Phenotype: The physical-appearance of the organisms Called phenotype.

Example:

     Eye color, Dominant character: The characters appeared in F1 generation and again reappear in F2 generation.

Recessive character:

     The characters disappeared in F1 generation.

Hybrid:

     Offspring produced by cross of parents possessing contrasting characters (opposite character) is called hybrid.

Chromosome:

   Meaning:

     Chromo mean color and soma mean body. So chromosomes is the name given to the structure as they readily absorb dyes and become colored.

Definition:

     Chromosome are thread like structure that appears inside the nucleus of cell only at the time of cell division.

Discovery:

     Chromosome were discovered by Waldeyer in 1876.

Numbering:

     Each species of plants and animals have certain number of chromosome Which is constant through out its somatic cells of the body. e.g. Human has 46, Potato has 8 and Drosophila (fruit fly) has 8 chromosomes.

 Composition:

● In prokaryotic cells chromosome consist of DNA and are not enclosed in a nuclear membrane.

³● In eukaryotic cell the chromosomes are found in the nucleus and are composed of chromatin materials which are chemically DNA and proteins.

Structure:

Chromatin materials:

    Chromosomes are composed of chromatin materials’ main component of chromatin materials are DNA and histone protein.

Nucleosome:

     Nucleosome is the unit of chromatin materials. Each nucleosome contains DNA and histone protein. Nucleosome is about 1 nm in diameter. Histone protein forms core of nucleosome.

Composition of nucleosome:

     Each nucleosome consist of 8 molecule of various types of histone proteins forming a octamer, around which two turns of about 200 nucleotides (unite of DNA) of double helical DNA is Wrapped to form a super helix.

     Nucleosomes are linked together like beads on a string. Two turn of DNA are sealed on the nucleosome by another type of histone protein called H1. Histones are positively charged due to basic amino acid (arginine, lysine), so histones are attracted by negatively charged phosphate groups of DNA.

Gene and Allele

Gene:

    A gene is the fundamental unit of heredity which present on chromosome. Gene is the segments of nucleic acids which consist of a specific sequence of bases and number of nucleotides that code for protein synthesis. The position of a gene on chromosome is called locus.

Allele:

   The alternate form of gene is called is Allele. Alleles originate by mutation. mutations are changes in genes taking place when a gene is being replicated, even a single base pair is not present in correct order. It may alter the character of whole gene which results in production of another form of that gene.

Role of gene in protein synthesis:

Protein:

    Protein are organaic in nature. These are the most organic substances in the cell.

Amino acid:

    The building blocks of protein is called Amino acid. There are twenty 20 amino acids which combine together in a specific way and form different protein. A gene encodes instruction for building a specific protein.

Steps of protein synthesis:

     Protein synthesis is complete in two major steps. These steps are:

1. Transcription

2. Translation

1. Transcription:

        The formation of messenger RNA (mRNA) from DNA is known as transcription. 

        During transcription, the double DNA strands of a gene that codes for a protein synthesis unzip from each other. One of the two strands give rise to messenger RNA (mRNA). In messenger RNA the base thymine (T) is replaced by uracil (U).

2. Translation:

      The formation ot protein from mRNA is called translation. When messenger RNA is formed, it moves from nucleus to cytoplasm through nuclear pores and attaches to ribosomes.

      In ribosome, the mRNA codes are translated by transfer RNA (tRNA) code which in turn is transferred into a protein sequence. ln this process of protein synthesis, each set of mRNA base (codon) will pair with a complimentary tRNA base (anticodon). Each tRNA is specific for amino acid. Amino acids are linked together by peptides bonds and eventually the required protein is formed.

Codon And Anticodon

CODON:

      A group of three bases (triple) in mRNA which specify an amino acid is called Codon.

Example:

     AUG is a codon for amino acid methionin.

 ANTICODON:

      The tRNA bears three bases which pair with complimentary bases in mRNA during protein synthesis. They are called anticodon.

inheritance, 

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