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Dominant and recessive alleles are key to understanding basic genetics. Alleles are different forms of a gene. In our pea plant example, we have two alleles for seed color: one for yellow (Y) and one for green (y).
Dominant alleles like Y will always mask the presence of recessive alleles like y. This means if a plant has at least one Y allele, it will show the yellow seed color.
In genetics, dominant alleles are usually represented by uppercase letters, while recessive alleles are represented by lowercase letters.
Understanding this helps us predict the traits offspring might inherit from their parents.

Genotype determination is figuring out the genetic makeup of an organism. For our pea plants, we need to know the combination of alleles each plant has.
True-breeding yellow seed plants are homozygous dominant (YY), while true-breeding green seed plants are homozygous recessive (yy).
When these plants are crossed, each parent contributes one allele to the offspring, making the genotype of the first-generation (F1) plants heterozygous (Yy).
This is important because the genotype directly affects the phenotype, which is the observable trait such as seed color.

Genetic inheritance explains how traits are passed from parents to offspring. Mendel's laws of inheritance, based on his pea plant experiments, lay the foundation.
The law of segregation states that allele pairs separate during the formation of gametes (egg and sperm cells). Each gamete carries only one allele for each gene.
In our pea plant scenario, the yellow seed parent (YY) and the green seed parent (yy) each contribute one allele to their offspring.
The possible combinations rely on the Punnett Square, a tool that helps visualize all potential genotypes of the offspring and understand the probability of each trait appearing.

Pea plant genetics became a cornerstone of modern genetics through Gregor Mendel's experiments. He chose pea plants due to their distinct varieties and ease of breeding.
Pea plants have several characteristics that make them ideal for genetic study, like seed color, which can be either yellow or green.
Mendel discovered that crossing a true-breeding yellow plant (with genotype YY) and a true-breeding green plant (with genotype yy) would result in all yellow offspring (Yy) because yellow is dominant.
This set the stage for understanding dominant and recessive traits in other organisms as well. The simplicity of pea plant genetics helps illustrate fundamental genetic principles very clearly.

True-breeding parents have consistent traits over many generations. This means their genotype is homozygous, having two identical alleles for a specific trait.
In our example, a true-breeding yellow seed plant has the genotype YY, and a true-breeding green seed plant has the genotype yy.
When these true-breeding plants are crossed, all offspring in the first generation (F1) inherit one allele from each parent. Therefore, all F1 plants are heterozygous (Yy) and show the dominant yellow seed color.
True-breeding plants simplify genetic studies because their traits are predictable, making it easier to observe patterns of inheritance.