The Humans Genetic DNA and RNA

The Humans Genetic DNA and RNA

The Humans Genetic DNA and RNA

Each organism has many such qualities, which are transmitted from parents to their children from generation to generation. Such properties are called hereditary characters or ancestral properties. The transmission of the basic properties of organisms from one generation to another is called Heredity. Due to transmission of basic qualities, the properties of each organism are similar to the properties of their parents. The transmission of these properties from one generation to the next is through gametes. Therefore, the transmission of heritable traits through parents from generation to generation in their offspring is called heredity.

The branch of biology under which heredity and variations are studied is called genetics. Gregor John Mendel laid the foundation for modern genetics with his scientific discoveries. That is why he is called the father of genetics.

Mendel’s Law of Inheritance Mendel’s Law of Inheritance

Gregor John Mendel (Gregor John Mendel, 1822–84) was the pastor of a monastery of Christians in a place called Brunn in the country of Austria. He founded modern genetics with his scientific discoveries. In 1866, he published the findings of his experiments on pea plants in the Annual Proceedings of the Natural History society or brunn, but this was ignored in the science world for 34 years. The findings of his experiments were recognized by scientists after his death in 1900 AD.

Mendel chose seven pea traits for his experiments, with one of the pairs having the ability to suppress the other property during the experiment. He called the first Dominant and the second Recessive property. Mendel expressed these factors with a symbol responsible for the inheritance of the properties. Among the pairs of qualities, he expressed the factor of effective symptom in English capital letters and the factor of ineffective character with small letters of English. For example, ‘T’ for tallness and ‘t’ for dwarfism.


The Humans Genetic DNA and RNA


Dominanat Characters Recessive Characters
Spherical Seeds Smooth Seeds Wrinkled Seeds
Cotyledon yellow green
Flower Color Red White
Pod shape smooth narrowed
Pod color green yellow
Flower position orbital anterior
Plant length Tall dwarf

According to Mendel, each reproductive cell has two factors to express the same quality. When both these factors are equal, this condition is called Homozygous and when they are opposite, this condition is called Heterozygous.


ТТ – Homozygous

Tt – Heterozygous

Mendel first studied the inheritance of one pair of opposite properties and then two pair of opposite properties, which are called monogamous crosses and symmetric crosses, respectively.

Monohybrid cross: When a unit is hybridized between two plants on the basis of characteristics, it is called a unicameral cross. In a narrow cross, Mendel selected two species of pea plants that had one tall (Tall) and the other dwarf in pairs of opposite traits, and if they were cross-linked, it was seen that the seeds in the first generation (F1 Generation) The plants produced by them were all tall. All these first generation plants are called F1 plants. He then cultivated the plants from the F1 generation by self pollination and found that the tall and short plants found in the second generation F2 had a phenotypic ratio of 3: 1. This type of ratio is also known as Monohybrid Ratio. Three tall plants had one pure tall, TT and two mixed or hybrid tall, Tt. A dwarf plant made from the F2 generation was a pure dwarf.

Third Generation

If we get the third generation from the plant of F2 i.e. F3, then we will see that pure tall plants (TT) always make tall plants. Similarly, pure dwarf plants (tt) always make dwarf plants, but if cross mixed tall plants (Tt × Tt) are made, then F will be 3: 1 phenotypic ratio of tall and dwarf plants like generation.

Three tall and one dwarf plants of the F2 generation had one pure tallow (TT), two mixed tallow (Tt) and one pure dwarf (tt) with a ratio of 1: 2: 1. F3 Pure tall plants are obtained only when crossed with pure tall. like-

TT × Tr → TT

F3 is obtained from pure stocky plants when crossed with pure stock. like-

tt × tt → tt

But by crossing the mixed taller (Tt) with the mixed taller (rt), only the tall and dwarf (short) plants are obtained in the ratio of 3: 1. in this-

TT – Always pure tall (Homozygous tall)

Then Tt – Heterozygous tall

tt – always pure dwarf (Homozygous dwarf)

Ratio of

Phenotypic ratio – 3: 1 (3 long and 1 dwarf)

Genotypic ratio – 1: 2: 1 (1 pure long, 2 mixed long and 1 pure dwarf)

Perforated Cross Dihybrid Cross

In this, two pairs of opposite symptoms are crossed. Mendel cross-pollinated plants produced from round and yellow seeds and green and wrinkled seeds for a bicameral cross. In this, round and yellow seeds are effective. Both plants are represented by RRYY and rryy respectively. It is clear that the gametes of the first plant will have the RY factor and the second plant gametes will have the ry factor.

When artificial cross-pollination was carried out in these two plants, all the plants derived from the seeds produced were round and yellow hybrid seeds. Here wrinkled and green color was recessive quality. Therefore, they remained hidden in the F1 generation, but the round and yellow color had effective properties, due to which they appeared. Now self-pollination was allowed in this F1 generation plants and F2 generation plants were obtained. According to the separation rule, four types of seeds were made, whose ratio was as follows – round + yellow seed = 9

Round + Green Seed = 3

Wrinkled + yellow seed = 3

Jhurindar + Green seed = 1

Round-yellow and wrinkled-yellow seeds had a ratio of 3: 1. Round-green and jhurindar-green seeds also had a ratio of 3: 1.

Mendel’s Laws Mendel’s Law

Based on the Monohybrid cross and Dihybrid cross, Mendel formulated certain hereditary rules, known as Mendel’s law of Inheritance. In these rules, the first and second is based on a single cross and the third rule is based on a bicameral cross.

Law of Dominance

Under this, Mendel made a cross in keeping with the opposite symptoms of a couple, then the symptom present in the first generation was effective. For example, when a dwarf plant was cross-fed with a tall plant of peas, only tall plants emerged in the first generation. This made the Dominance long and dwarf ineffective according to the rules.

Mendel’s Law of segregation

According to this rule, when the gametes are formed, the factors of the pair of factors (genes) are separated and only one of these factors reaches the gametes. Both factors never go together in a coupler. This law is also called the law of purity of gametes. For example, when the tall plant of peas is crossed with a dwarf plant, only the tall plants grow in the F1 generation, but again when self-pollinated in the flowers of the same generation, the F2 generation plants are of both types. Here a ratio of 3: 1 is found in tall and dwarf plants.

Law of independent assortment

According to this rule, different pairs of factors that are found in an organism are independent of each other and can be mixed freely to form new-colored organisms.

Sex determination in humans Sex Determination in Human

The total number of chromosomes in humans is 46. Each child gets one chromosome of each pair of homologous chromosomes from the mother through the egg and the other by the sperm from the father. In spermatogenesis, two types of sperm are formed by meiosis – half of which the 23rd pair contains the X-chromosome (ie 22 + X) and half of which the 23rd pair contains the Y-chromosome (ie 22 + Y). ).

In females, there are similar type of chromosomes ie (22 + X) and (22 + X). If the egg meets the sperm with the X-chromosome at the time of fertilization, the 23rd pair in the zygote will be XX and the offspring formed will be the girl. Conversely, if an egg is fertilized by a sperm with a Y-chromosome, then the 23rd pair in the zygote will be XY and the offspring formed from it will be a boy. Therefore, the chromosome of the male is responsible for determining sex in the child.


Variation is the qualities of an organism that show it to be different from its parent or other members of its own caste from the original nature of the same quality.

Causes of variation: The gene is the determinant of the hereditary properties of all organisms. Variation is transmitted from one generation to another through genes. Therefore, duplication of genes is the main reason for variation. Dividing of genes is essential for cell division and division of cells is essential for reproduction. Therefore, transmission of variation takes place from one generation to another due to reproduction. Variations are usually seen only in children born of sexual reproduction. The clearly visible variations in generation resulting from asexual reproduction, such as vegetative propagation, are commonly found.

Types of Variations: There are two types of variations. These are

Germinal variation and
Somatic variation
Genetic variation Germinal Variation

Such variations occur due to changes in germ cells. Such variations are inherited from one generation to another. For this reason genetic variation is also known as Genetic variation. Some of such variations appear from birth itself, such as the color of eyes and hair, while some variations appear after birth, such as anatomical formation, body length, etc.

Somatic variation Somatic Variation

Such variations can appear due to many reasons, such as the effect of climate and environment, types of food available, interaction with other living organisms, etc. Such variations are not caused by changes in the properties of the chromosome or gene. Therefore, such differences are not inherited from one generation to another. Such variations are acquired. For this reason, they have no importance in Evolution.

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Sources of Genetic Variation

Genetic variation in organisms is due to Mutation and they contribute significantly to the development of new species. Changes in the structure and position of genes present on the chromosome or chromosome are the cause of mutation. Genetic recombination is also another reason for genetic variation. Due to genetic recombination, the properties of genes in chromosomes of offspring may differ from the properties of genes of their parents. Such new properties can help organisms adapt according to their environment. Sometimes such new properties are not helpful for the organisms to adapt to the environment. In such a situation, due to mutual competition, disease etc., such organisms become extinct in the race of development. The remaining organisms transmit such beneficial qualities to their offspring. In this way, nature selects some organisms with new properties and expels some.


The Humans Genetic DNA and RNA | The Humans Genetic DNA and RNA

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