The features examined by Gregor Mendel

Figure The Seven Traits that Mendel Studied in Pisum Sativum

(Courtesy of Ricochet Productions)

Mendel examined the quantitative laws of inheritance. In his first experiment, he crossed two pea plants that possessed true-breeding variants of seed shape. These were the round and wrinkled variants. When plants producing round seeds and plants producing wrinkled seeds are crossed, they yield plants that produce round seeds. The presence of all round seed plants in the first generation (F₁ generation) indicated that the traits were not blending together. If they were, there should be plants of intermediate seed. When the round-seed-producing plants of the first generation were crossed with one another, the plants of the second generation (F₂ generation) demonstrated a yield of 3/4 round-seed-producing plants and 1/4 wrinkled-seed-producing plants.

Figure 1.3 Mendel’s Single-Trait Crosses

(Courtesy of Ricochet Productions)

Table

The Results of Mendel’s Crosses

Trait F₁ Generation F₂ Generation Ratio

Seed color 100% yellow 6,022 yellow: 2,001 green 3.01:1

(green or yellow)

Seed shape 100% smooth 5,474 smooth: 1,850 wrinkled 2.96:1

(wrinkled or smooth)

Flower color 100% purple 705 purple: 224 white 3.15:1

(purple or white)

Flower position 100% axial 651 axial: 207 terminal 3.14: 1

(axial or terminal)

Pod color 100% green 428 green: 152 yellow 2.82:1

(yellow or green)

Pod shape 100% inflated 882 inflated: 299 pinched 2.95:1

(inflated or constricted, pinched)

Plant height 100% tall 787 tall: 277 dwarf 2.84:1

(tall or dwarf)

Each of the crosses yielded approximately a 3:1 ratio in the second generation. Mendel repeated his experiment many times so as to increase the number of offspring. Statistical approach raised the validity of his works tremendously.

With the crossing can be established:

1) dominant or recessive trait and corresponding gene;

2) the genotype of an organism;

3) the interaction of genes and the nature of this interaction;

4) the phenomenon of genes linkage;

5) the distance between genes;

6) genes linked with sex.

3. The laws of Gregor Mendel

The law of hybrids uniformity in the first generation (dominance law)

Three basic principles of inheritance were established, or supported, by Mendel’s monohybrid crosses.

His results clearly indicated that in the first generation, one of the two variants of the trait dominated the other, or recessive, trait. This is called dominance.

The results of single-trait crosses clearly indicated that the genetic material was not being blended. Blending would cause traits to be lost or modified in later generations, and Mendel’s experiments demonstrated that recessive traits remained intact from generation to generation, although they may not be evident due to the presence of a dominant trait in the individual. This provided support for a particulate theory of inheritance, in which the genetic material is a physical structure passed on from generation to generation. These particles are called genes.