<h2>Garden Pea Characteristics Revealed the Basics of Heredity</h2>
In his 1865 publication, Mendel reported the results of his crosses involving seven different characteristics, each with two contrasting traits. A trait is defined as a variation in the physical appearance of a heritable characteristic. The characteristics included plant height, <a data-lesson="summarizing-evolution-of-seed-plants" data-subject="biology" data-tutorial="seed-plants" href="https://app.ulearngo.com/biology/seed-plants/summarizing-evolution-of-seed-plants">seed</a> texture, seed color, flower color, pea pod size, pea pod color, and flower position. For the characteristic of flower color, for example, the two contrasting traits were white versus violet. To fully examine each characteristic, Mendel generated large numbers of F1 and F2 plants, reporting results from 19,959 F2 plants alone. His findings were consistent.
What results did Mendel find in his crosses for flower color? First, Mendel confirmed that he had plants that bred true for white or violet flower color. Regardless of how many generations Mendel examined, all self-crossed <a data-lesson="reproduction-methods" data-subject="biology" data-tutorial="reproductive-system" href="https://app.ulearngo.com/biology/reproductive-system/reproduction-methods">offspring</a> of parents with white flowers had white flowers, and all self-crossed offspring of parents with violet flowers had violet flowers. In addition, Mendel confirmed that, other than flower color, the <a href="https://app.ulearngo.com/tutorials/introducing-genetics/pea-plants">pea plants</a> were physically identical.
Once these validations were complete, Mendel applied the <a data-lesson="pollination-and-fertilization" data-subject="biology" data-tutorial="plant-reproduction" href="https://app.ulearngo.com/biology/plant-reproduction/pollination-and-fertilization">pollen</a> from a plant with violet flowers to the stigma of a plant with white flowers. After gathering and sowing the seeds that resulted from this cross, Mendel found that 100 percent of the F1 hybrid generation had violet flowers. Conventional wisdom at that time would have predicted the hybrid flowers to be pale violet or for hybrid plants to have equal numbers of white and violet flowers. In other words, the contrasting parental traits were expected to blend in the offspring. Instead, Mendel’s results demonstrated that the white flower trait in the F1 generation had completely disappeared.
Importantly, Mendel did not stop his experimentation there. He allowed the F1 plants to self-fertilize and found that, of F2-generation plants, 705 had violet flowers and 224 had white flowers. This was a ratio of 3.15 violet flowers per one white flower, or approximately 3:1. When Mendel transferred pollen from a plant with violet flowers to the stigma of a plant with white flowers and vice versa, he obtained about the same ratio regardless of which parent, male or female, contributed which trait. This is called a reciprocal cross—a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross. For the other six characteristics Mendel examined, the F1 and F2 generations behaved in the same way as they had for flower color. One of the two traits would disappear completely from the F1 generation only to reappear in the F2 generation at a ratio of approximately 3:1 (see the table below).
<table summary="">
<thead>
<tr>
<th colspan="5">The Results of Mendel’s Garden Pea Hybridizations</th>
</tr>
<tr>
<th>Characteristic</th>
<th>Contrasting P0 Traits</th>
<th>F1 Offspring Traits</th>
<th>F2 Offspring Traits</th>
<th>F2 Trait Ratios</th>
</tr>
</thead>
<tbody>
<tr>
<td>Flower color</td>
<td>Violet vs. white</td>
<td>100 percent violet</td>
<td>
<ul data-bullet-style="none">
<li>705 violet</li>
<li>224 white</li>
</ul>
</td>
<td>3.15:1</td>
</tr>
<tr>
<td>Flower position</td>
<td>Axial vs. terminal</td>
<td>100 percent axial</td>
<td>
<ul data-bullet-style="none">
<li>651 axial</li>
<li>207 terminal</li>
</ul>
</td>
<td>3.14:1</td>
</tr>
<tr>
<td>Plant height</td>
<td>Tall vs. dwarf</td>
<td>100 percent tall</td>
<td>
<ul data-bullet-style="none">
<li>787 tall</li>
<li>277 dwarf</li>
</ul>
</td>
<td>2.84:1</td>
</tr>
<tr>
<td>Seed texture</td>
<td>Round vs. wrinkled</td>
<td>100 percent round</td>
<td>
<ul data-bullet-style="none">
<li>5,474 round</li>
<li>1,850 wrinkled</li>
</ul>
</td>
<td>2.96:1</td>
</tr>
<tr>
<td>Seed color</td>
<td>Yellow vs. green</td>
<td>100 percent yellow</td>
<td>
<ul data-bullet-style="none">
<li>6,022 yellow</li>
<li>2,001 green</li>
</ul>
</td>
<td>3.01:1</td>
</tr>
<tr>
<td>Pea pod texture</td>
<td>Inflated vs. constricted</td>
<td>100 percent inflated</td>
<td>
<ul data-bullet-style="none">
<li>882 inflated</li>
<li>299 constricted</li>
</ul>
</td>
<td>2.95:1</td>
</tr>
<tr>
<td>Pea pod color</td>
<td>Green vs. yellow</td>
<td>100 percent green</td>
<td>
<ul data-bullet-style="none">
<li>428 green</li>
<li>152 yellow</li>
</ul>
</td>
<td>2.82:1</td>
</tr>
</tbody>
</table>
Upon compiling his results for many thousands of plants, Mendel concluded that the characteristics could be divided into expressed and latent traits. He called these, respectively, dominant and recessive traits. Dominant traits are those that are inherited unchanged in a hybridization. Recessive traits become latent, or disappear, in the offspring of a hybridization. The recessive trait does, however, reappear in the progeny of the hybrid offspring. An example of a dominant trait is the violet-flower trait. For this same characteristic (flower color), white-colored flowers are a recessive trait. The fact that the recessive trait reappeared in the F2 generation meant that the traits remained separate (not blended) in the plants of the F1 generation.
Mendel also proposed that plants possessed two copies of the trait for the flower-color characteristic, and that each parent transmitted one of its two copies to its offspring, where they came together. Moreover, the physical observation of a dominant trait could mean that the genetic composition of the organism included two dominant versions of the characteristic or that it included one dominant and one recessive version. Conversely, the observation of a recessive trait meant that the organism lacked any dominant versions of this characteristic.
So why did Mendel repeatedly obtain 3:1 ratios in his crosses? To understand how Mendel deduced the basic mechanisms of inheritance that lead to such ratios, we must first review the laws of probability.

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Garden Pea Characteristics Revealed the Basics of Heredity

Biology studies life and living organisms. Biology can be divided into different sections that cover the morphology, physiology, anatomy, behavior, and so on of living organisms.

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Discover the basics of genetics and learn about Mendel’s experiments and his model system, which includes Mendelian crosses, probability basics, and the laws of probability, along with characteristics and traits, phenotypes and genotypes, and the Punnett square approach.


Garden Pea Characteristics Revealed the Basics of Heredity

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