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 Heredity and Evolution

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• New indivisuals are produced by reproductive process, which are similar to parents but something differ. 
• We get more diversities by sexual reproduction. 
• Selection of variants by environmental factors forms the basis for evolutionary processes. 

Genetics: Genetics is the study of heredity and variation. 

Heredity: Transmission of characters/traits from one generation to the next generation is called heredity. 

Variations: The differences in the characters/traits between the parents and offspring are called variations.

Inherited Traits : Those special traits with basic traits which inherited from their parents are callled inherited traits. 

Example: Free and attached earlobes in human, colours of skin, colours eyes etc.

Types of variations: There are two types of variations.

(i) Somatic Variation: 

(ii) Gametic Variation: 

Differences between Somatic Variation and Gamatic Variation

Somatic Variations: 

(i) This variation comes in body cells. 

(ii) They do not inherit in the next generations. 

(iii) They are not helpful in evolution. 

(iv) These are also called aquared traits. 

(v)  Example, boring of pinna, cutting of tails in dogs.

Gametic Variations: 

(ii) This variation comes in reproductive cells. 

(ii) They inherit in the next generations. 

(iii) They are helpful in evolution. 

(iv) They are also called genetic traits. 

(v)  Example, human height, skin colour.

Accumulation of variation during reproduction : 

Variations accumulate during reproduction in the offspring. In asexual reproduction new indivisuals are quite similar and there are less variations. Because;

(i) There generated very less errors (inaccuracy) during DNA copying.

(ii) Involving of single parent. 

While if sexual reproduction is involved, even greater diversity will be generated. The reasons are as follow;

(i) large variations appear due to large errors. 

(ii) Diversity comes due to cross breeding and involving of male and female gamate. 

(iii) Separation of chromosomes.   

Mendel's Experiment And Rule for Inheritance of Traits: 

Mendel's porposed some majors rule for inheritance. He is the father of genetics. Mendel used a number of contrasting characters for garden pea. He selected peas (Pisum Sativum) plants for his experiment. This is why that :

(i) Peas plants are annual plants

(ii) These complete their life cycle in one season and give fruits and flowers.

(iii) There are variety of species of peas plants and all traits are macroscopically visible. 

(iv) Normally allows self-fertilisation but cross-fertilisation can also be
carried out.

Examples: round and wrinkle seed, tall and short, while flower and purple and yellow seed and green seed plants. 

Mendel used seven alternative (contrasting) characters of pea plants for his experiment which as follow:

Rules for inheritance of traits: 

(i) The rule for inheritance in human being is based on this that the parents transfer equal amount of genetic materials in the offspring.

(ii) There are two options for each traits in the each offspring. 

(iii) Each trait is impressed by the DNA of parents. 

Mendel's Experiments and Hybrid Method: 

There are two kinds of hybrid mehtod :

(i) Monohybrid Cross: 

(ii) Dihybrid Cross:  

1. Monohybrid Cross : When the Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross.

Example : Plants of round and wrinkle seed, plants of tall and twarf etc. 

2. Dihybrid Cross : When the cross is taken place by taking double traits of two plants is called dihybrid cross. 

Example Round and green plants with wrinkled and yellow plants. 

 

Inherited Traits

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Dominant Traits : Those inherited traits of parents which are visible in the offspring, called dominant traits. 

Recessive Traits : Those inherited traits of parents which are hiden in the offspring are called recessive traits. 

Example: short plant (t) in Mendel's experiment.

Genotype: Gynotype is a group of genes which is responsible for a special characteristic. It is a genetic information present in cells and It is not visible directly in the indivisual.

Examples of genotypes: 

(a) The gene responsible for colour of eyes. 

(b) The gene responsible for colour of hair. 

(c) The gene responsible for height.

(d) The gene responsible for the heridetory(genetic) diseases.

How to make genotype changes. 

(a) Changing in gene and chromosome. 

(b) Recombination of gene. 

(c) Hybriding of gene.    

Phenotypes: Those visible traits which are seen in the organism and depends on genotype is called phenotype traits. 

But it can be influenced by the envirmental factors. This is the manifestation of the informations of gene. It can be found by simple observation. 

Examples: colour of eyes, colour of hair, height, voice, some diseases and some fixed behavior. 

Differences Between Inherited Traits: 

Acquired Traits: 

1. These are the traits which are developed in an individual due to special conditions
2. They cannot be transferred to the progeny(offspring).
3. They are helpful in evolution
eg. Low weight of starving beetles.

Inherited Traits: 

1. These are the traits which are passed from one generation to the next.
2. They get transferred to the progeny(offspring).
3. They are helpful in evolution.
eg. Colour of eyes and hair

Monohybrid cross in Mendel's Experiment : 

In this experiment Mendel's had taken two pea plants of single character of tall and short plant as parent plants. All plants are tall as tall as parent. Mendelian experiments test this by getting both the parental plants and these F1 tall plants to reproduce by self-pollination. The second-generation, or F2, progeny of the F1 tall plants are not all tall. Instead, one quarter of them are short. This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. 

Ratio of characters in Mendelian experiment: 

There are following ratios of characters of plants grown in F₂ generation on the basis of genotype and phenotype in Mendel's monohybrid cross test.

Phenotype : Tt Tt Tt tt (3 : 1) 

3 tall and 1 short plant

Genotype: Tt Tt Tt tt (1: 2 : 1) 

Genetically 1 tall (TT) : 2 tall (Tt) : 1 short (tt)  

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1. Homologous Organs: Those organs in the various organisms which have same structure and origin and different functions are called homologous organs. 

Example : Fore limb of frogs, feather of birds, Fore limb of horse are same originated but have difference functions. 

2. Analogous Organs: Those organs of various organisms which have same function and but have different in oriigin are called analogous organs. 

Example : wings of butterfly and wings of birds have same functions but differ in origin.

3. Fossils: The preservative traces of dead organnisms are called fossils. 

Example: If a dead insect gets caught in hot mud, for example, it will
not decompose quickly, and the mud will eventually harden and retain
the impression of the body parts of the insect. 

Some Examples of obtain fossils: 

(1) Fossil - tree trunk

(2) Fossil - invertebrate (Ammonite)

(3) Fossil - invertibrate (Trilobite)

(4) Fossil - fish (Knightia)

(5) Fossil - dinosaur skull (Rajasaurus)

Fossils also provide evidence  

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