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how does the mechanism of heredity work ?

The mechanism of heredity involves two important steps and these are:

1. Transmission of genes

Sexual reproduction, as we know, involves the fusion of cells. As a result, the amount of DNA in the zygote doubles.

In order to maintain the amount of DNA, the fusing cells should contain half the amount of DNA, so that the resulting zygote has the same amount of DNA as the parent cell. Each cell in our body has two factors or genes for each characteristic (T or t) as separate independent pieces called chromosomes. Thus each cell will have two copies of each chromosome, one each from the male and female parents. 

These chromosomes separate to form two gametes. Then, gametes from both the parents fuse to form a zygote, which develops into a new individual.

Therefore, when two gametes of the germ cells combine, the normal chromosome number is restored.

Every somatic (body) cell of the human body has 23 pairs (46) of chromosomes.

2. Mechanism of heredity at cellular level

The heredity material in the form of DNA is present inside the nucleus of a cell. The segment of DNA, which gives information for synthesis of protein inside a cell, is called the gene of that protein. These proteins control all the characteristics of an organism.

We have already studied that in both plants and animals, growth or height of the body is controlled by hormones.

Formation of short and tall plants

Thus, the height of a plant depends upon the quantity and type of a specific plant hormone. This quantity and type of hormone depends upon enzymes present to trigger the rate of production of hormones.

It is ultimately a gene that controls the amount of enzymes. If more enzymes are produced, then the plant grows taller.

If any variation or alternation in a gene occurs, then the enzyme produced is less efficient. Hence, the plant is short in height.

 

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Cellular DNA is the information source for making proteins in the cell. A section of DNA that provides information for one protein is called the gene for that protein.

Traits are coded in the form of genes, genes are sequences which would code for particular polypeptide which would eventually lead to the formation of particular proteins, proteins would then lead to the expression of particular trait. For example trait for skin colour is determined by genes which code for enzyme which make melanin (skin pigment).

DNA contain two alleles ( genes located at the homologous pair responsible for the contrasting character) these include the recessive and the dominant gene. in which the dominamt gene forms the proteins which helps the particular trait to get expressed. whereas the rcessive genes form a less effective protiens thus itscharacter or trait is not expressed.

for example if the plant contains the alele as (Tt) then T is dominant and its character tallness is shown by the plant.

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. Chromosomes are the vehicles of heredity.

2. Genes are the units of heredity.

3. Segregation of chromosomes take place during gamete formation.

4. Gametes are formed after meiosis

5. Recombination of genes take place during the formation of gametes.

6. Half of the genetic material is contributed by mother and half by father.

pg no 145

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The mechanism of heredity work in the following ways-

1.They transfer characters from parent to offsprings in the form DNA.

2. DNA is the basic unit of inheritance, during reproduction this DNA copies itself in the offspring, its similar to the main DNA , similar because there may be some errors too.

3. Moreover in Sexual reproduction the DNA of both parents work inheriting the characters of both parents.

4. It also helps in providing such offsprings which are similar to the parents. One of most important benefit is that it helps the offsprings in the current surroundings

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