Mendel's first law, also called Factor Segregation Law, was formulated by Gregor John Mendel and was published between 1865 and 1866.
This law states that each characteristic of the human being is determined by a pair of factors that are separated in the formation of gametes.
Each gamete - from the mother and the father - carries only one factor (gene), which, when united, determines the characteristic of that new individual. To reach this conclusion, Mendel performed crosses with peas.
Mendel's discoveries enabled great advances in studies on heredity, that is, about how characteristics are passed from generation to generation. For this reason, Mendel is considered the father of genetics.
See what this law says:
All characteristics of an individual are determined by genes that segregate, separate, during the formation of gametes, so that the father and mother transmit only one gene to their descendants.
Mendel's experiments
Mendel was interested in knowing how characteristics were transmitted from generation to generation and for this he experimented with
sweet peas (pisum sativa). The characteristics of this plant that made your experience successful are:- Short life cycle;
- Capable of self-fertilization;
- Easy cultivation;
- Large number of descendants;
- Easy to see colors and shapes.
To do the experiment, Mendel used pure lineage plants. To be sure that they were pure, it was necessary that for 6 generations the individuals generated by fertilization had the same characteristic.
For example, if over 6 generations the yellow seed plants generated only yellow seed plants, they were considered pure. If among these 6 generations any plant had green seeds, the plant would not be used in the experiment.
After two years of checking the purity of the plants, Mendel started crosses to understand how the characteristics are transmitted between generations. In each experiment, Mendel analyzed only one feature, see what characteristics were analyzed in these experiments:
- Seed color;
- Seed texture;
- Shape of the pods;
- Integument color;
- pod color;
- Height of plants;
- Position of flowers.
The color of pea seeds
To carry out the experiment with the characteristic "seed color", Mendel crossed a pure green seed (vv) with a pure yellow seed (VV). These two seeds are considered the parental generation.
All seeds originated from this fertilization were yellow (Vv) and this generation was called F1. These seeds were considered hybrids, as they were descendants of plants with different characteristics.
Then, the F1 seeds were self-fertilized and the result of this crossing was: 3 yellow seeds and 1 green seed, that is, 75% yellow and 25% green. See the diagram below:
From this experiment, Mendel concluded that there were two factors that determined the color of pea seeds, one of which was dominant, yellow, and other recessive, the green.
Conclusions from Mendel's First Law
- Each characteristic of an individual is determined by a pair of genes (or factors);
- Individual characteristics are hereditary;
- Characteristics are transmitted by genes;
- Individuals inherit one gene from the father and one gene from the mother for each trait.
Thus, we can say that all the characteristics of individuals, such as hair color, color of eyes or nose shape, are formed by a pair of genes, one of them coming from the mother, the other of Father.
The separation of these genes takes place through the process of meiosis that splits the gamete in two. At the moment of fertilization, the gametes unite and form a pair of factors, which will determine the character of the new individual.
know more about gene.
Exercises of Mendel's First Law
1 - When crossing two yellow hybrid peas (Vv), which will be the descendants? Consider the green color to be characteristic of the recessive gene.
a) 100% Vv yellow;
b) 50% yellow Vv; 50% green vv
c) 25% yellow VV; 50% yellow Vv; 25% green vv
d) 75% yellow Vv; 25% green vv
Resolution:
The crossing of two yellow hybrid peas (Vv x Vv) results in the following combinations:
- Yellow VV; yellow Vv; yellow Vv; green vv.
Therefore, the correct answer is the letter c.
2 - The crossing of hybrid yellow peas (Vv) with green peas (vv) generates the following offspring:
a) 50% yellow Vv; 50% green vv
b) 75% yellow Vv; 25% green vv
c) 50% yellow VV; 50% green vv
d) 25% yellow Vv; 75% green vv
Resolution:
The crossing of a hybrid yellow pea and a green pea (Vv x vv) generates the following offspring:
- Yellow Vv; yellow Vv; green vv; green vv.
Therefore, the correct answer is the letter a.
What are Mendel's laws?
The conclusions reached by Mendel from the crossing of plants were described in three laws, see what Mendel's second and third law say:
Mendel's Second Law
For the formulation of the second law, Mendel crossed plants with different characteristicsIn this case, yellow and smooth pea seeds and green and wrinkled peas.
In the F2 generation of this cross, smooth and wrinkled green seeds and smooth and wrinkled yellow seeds were originated. This result led to the finding that the characteristics are determined independently each other.
Also called Law of Independent Segregation of Genes or Diibridism, this law has the following statement:
Differences in one feature are inherited independently of differences in other features.
Mendel's Third Law
Mendel's Third Law, also called Independent Distribution Law, states that the dominant factor determines the characteristics of hybrid individuals.
Hybrid individuals are those that have a recessive factor and a dominant factor. In these cases, the dominant factor masks the recessive and manifests itself as a phenotype.
The third law is considered a summary of the first two laws and is used for educational purposes. For this reason, it is common to find materials that consider the existence of only two laws.
Learn more about mendel's laws.
Who was Gregor Mendel?
Mendel (1822 - 1884) was an Austrian, the son of peasants and entered the monastery of the Order of St. Augustine when he was 21 years old. Due to contact with his parents' work, he developed an interest in plants at an early age.
Upon entering the Olmutz Philosophy Institute, he was able to deepen his studies on plants and in 1843 he began to teach natural science subjects and devoted himself to plant breeding.
Due to his research and important contributions to the study of heredity, Mendel is considered the father of genetics.
See also the meaning of heredity, genome and DNA.
