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Mendel's Law

Published by: Nuru

Published Date: 06 Jul 2021

Mendel's Law in Class 10 Science

Mendel's Law

There are three Mendel's Law, they are Law of Dominance, Law of Segregation of Gametes or Law of Purity of Gametes, and Law of Independent Assortment.

  1. Law of Dominance
  2. Law of Segregation of Gametes or Law of Purity of Gametes
  3. Law of Independent Assortment

1. Law of Dominance

It states that "When the cross is made between two parents with one pair of pure contrasting characters, the hybrid is obtained. Hybrid shows the character of one of the parents phenotypically while the character of another parent remains hidden in the hybrid."

Example: When tall and dwarf pea plants are crossed in first-generation all plants are tall.

2. Law of Segregation of Gametes or Law of Purity of Gametes

It states that " Hybrid obtained as a result of a cross between two parents with one pair of pure contrasting characters contain the factor called gene for both contrasting characters. They remain together for a long time in a hybrid and segregate during gamete formation so that 50% gamete receives the gene for dominant character and remaining 50% gamete receives the gene for the recessive character."

Example: When hybrid tall pea are self-pollinated then both pure tall and dwarf are produced in F2 generation it is because of segregation of gamete.

3. Law of Independent Assortment

It states that " When two parents differ from each other in two or more pairs of contrasting characters or factors then the inheritance of one pair of factors is independent to that of other pair of factors."

Example: When the cross is made between tall red and dwarf white then tall red, tall white, dwarf red, and dwarf white are produced.

Sex-linked Disease

Certain hereditary characters found in human beings also depend on sex. Due to this, certain diseases are seen only in males and while others are seen only in females. Such diseases are called sex-linked diseases.

Example: Baldness can be seen only in males and breast cancer can be seen only in females.

Nucleic Acid

They are macromolecules that are hereditary determinants of living organisms. There are two types are:

  1. Deoxyribonucleic acid (DNA)
  2. Ribonucleic acid (RNA)

1. Deoxyribonucleic acid (DNA)

Gene is formed by a type of chemical substance deoxyribonucleic acid (DNA). It is double-stranded in structure. It is composed of a nitrogen base, phosphate, and sugar (deoxyribose).

The nitrogen bases of DNA are of four types, they are:

i. Adenine

ii. Thymine

iii. Guanine

iv. Cytosine

Adenine pairs up with thymine and guanine with cytosine. The difference in the sequence of nitrogen bases may bring about variation in the different organisms and even among the organism of the same species.

Functions of DNA

It transmits parental characters to their offspring.

2. Ribonucleic acid (RNA)

It is present in the cytoplasm or nucleolus or chromosome of a cell. It is single-stranded in structure. It is composed of ribose sugar.

The nitrogen bases of RNA are:

i. Adenine

ii. Guanine

iii. Cytosine

iv. Uracil

Functions of RNA

It takes part in protein synthesis.

Variation

The dissimilarities between parents and their offspring are called variations.

1. Hereditary Variation

The variation of organisms due to hereditary character is called hereditary variation. This type of variation is inherited from one generation to another generation through genes.

2. Environment Variation

The variation brought in the organism due to environmental factors like food, light, temperature, humidity, etc. is called an environmental variation.

3. Continuous Variation

The change in the characteristics of the offspring that occur slowly and gradually is known as continuous variation.

4. Dis-Continuous Variation (Mutation)

The change in the characteristics of the offspring suddenly due to the change in the organism is called a mutation.

The mutation causing factors are Ultraviolet rays, X-rays, Gamma rays, and different chemicals.

Example: A newly born baby without limbs, having an extra finger in hand, one-horned sheep, four-legged chicken, etc.

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