Genetics, Heredity and Evolution

GENETICS AND HEREDITY & Evolution 

 Basic Terms: 

HEREDITY: The process of transmission of characters  from  parents to their offsprings called as heredity.

Variation: The process of arising the difference among the individuals of same species is called as variation.

It is of two types:

1) Somatic variation: The variation arising externally in an organism i.e., the external visible variation of an organism are called as somatic variation.

2)Germinal variation : The internal variations which affect the genes of an organism are called as germinal variation.

EVOLUTION: The gradual change which occurs in organisms is called as evolution.

GENETICS: The branch of the biology which deals with the study of heredity and evolution is called as genetics.

Gregor Johann Mendel is known as the FATHER OF MODERN GENETICS.

GENE: Gene is a smaller part of DNA which carries all the traits of an organism. There are 23 pair of chromosomes in human beings.

Chromosomes: Chromosomes are thread- like structures present in the nucleus of the cell, which contains heredity information of the cell. The chromosome consist of two strands called as chromatids.

Karotype: The arrangement of chromosomes in the order of length and according to the position of the centromere is called as karotype.

Alleles: A pair of contrasting character is called as alleles.

Sex chromosomes: The pair of chromosomes which determine the sex of an individual is called as sex chromosomes.

Homozygous: An organism having identical alleles of genes is called as homozygous . For eg : human Female ( having XX chromosome) 

Heterozygous: An organism having different alleles of genes is called as heterozygous.  For eg : human male ( having xy chromosome) 

Genotype: The genetic makeup of an organism is called as genotype.

Phenotype: The external visible characters of an organism is called as phenotype.  It is a net result of interactions of genotype and environment in which an organism live.

Inheritance: Same as heredity

MENDEL’S MONO-HYDRID EXPERIMENT          

           

Across dealing with single character at a time is called as mono hybrid cross.

Mendel's Mono hybrid Cross

           Mendel took two pure line plants. He took a pure tall plant (TT) and pure dwarf (tt) . He cross pollinated these plants to get the plants of F1 generation.

He found that all the plants of F – 1 GENERATION WERE TALL. There was no short plant found in this generation.  

            In the next step Mendel allowed to self pollinate the plants of F-1 generation. To his surprise he found that there were both tall as well as short plants ( in the ratio of 3:1) in F-2 generation.

 This ratio is called as Mendel monohybrid ratio.

   The trait which express itself in both the generation is called as dominant trait whereas the trait which is not expressed in the f-1 generation But expressed itself in F-2 generation is called as recessive trait.

   In this way Mendel successfully explained the traits may be dominant or recessive.

Mendel’s Dihybrid Experiment

A cross  dealing with two characters at a single time is called as dihybrid cross.

                 In this cross Mendel studied two characters ( shape of seeds and colour of seeds ) simultaneously in a pea plant.

                 Mendel took two pure line plants having seeds round yellow( RRYY) and wrinkled green ( rryy) .

                    In the first step Mendel cross pollinated the pure round yellow and wrinkled green plants top get the plants  of F-1 generation.

       

                    

He found that all the plants in F- 1 generation have round and yellow seeds. And there was no plant having wrinkled and green seeds.

                       IN the next step Mendel allowed to self pollinate the plants of F-1 generation. To his surprise he found that there were four type of plants in F-2 generation. These were round yellow, round green, wrinkled yellow and wrinkled green and wrinkled green in the ratio of 9:3:3:1. This ratio is called Mendel dihybrid ratio.

 In this way Mendel successfully explain that the traits are inherited independently.

ORGANS AND THEIR TYPES

 Analogous organs: These are those organs which have different basic structural design but perform same function. For example: wings of the bats and wings of the birds have different basic structural design but perform same function. The similarity in the purpose indicates towards the same source of their origin. However the root may be different.

Analogous Organ

Homologous organs:  These are those organs which have same basic structural design but perform different function. For example:  Forelimb of birds and humans have same basic structural design but perform different functions. This similarity in design suggest that they might have originated from the same root.

Vestigial organs: These are those organs which were fully functional in our ancestors nut are reduce function or are function less in us. For example: third eyelid ( Nictating membrane), Appendix.

Nictating Membrane 

Mendel’s laws of inheritance

1.   Law of unit character:

     under process

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