Allele Interactions Explained with Punnett Squares

Welcome to our exploration of alleles and genetic dominance!Genes are specific sections of DNA that code for different traits.Each gene can have different forms called alleles. These alleles are alternative versions of the same gene.We represent alleles using letters. Capital letters represent dominant alleles, while lowercase letters represent recessive alleles.Let's use pea plant height as an example. Capital T represents the tall allele, which is dominant, while lowercase t represents the short allele, which is recessive.In complete dominance, the dominant allele masks the recessive allele. A plant only needs one copy of the dominant T allele to be tall.A plant's genotype can be TT, Tt, or tt. Both TT and Tt plants will be tall because of the dominant T allele, while only tt plants will be short.Now that we understand alleles and dominance, we're ready to explore how these traits are passed from parents to offspring.To understand inheritance patterns, we'll use a Punnett square to cross two heterozygous parents, each with genotype Tt.First, we create a two-by-two grid and place one parent's alleles along the side and the other's across the top.To fill in each square, we combine the alleles from the row and column. The first allele comes from Parent 1, the second from Parent 2.From our completed Punnett square, we can calculate the probability of each possible genotype in the offspring.One out of four offspring will be TT, or homozygous dominant.Two out of four will be Tt, heterozygous.And one out of four will be tt, homozygous recessive.When we consider phenotypes, both TT and Tt individuals will be tall, while only tt individuals will be short.Now let's explore more complex allele interactions, starting with incomplete dominance.In incomplete dominance, neither allele is completely dominant. When a red flower and a white flower cross, they produce pink offspring.Let's see how this appears in a Punnett square. We use R¹ for the red allele and R² for the white allele.When we cross two pink flowers, each parent contributes one R¹ and one R² allele.This gives us a one-to-two-to-one ratio of red to pink to white flowers.Now let's look at codominance, where both alleles are expressed simultaneously.In codominance, like in these flowers, both traits appear together, creating a spotted pattern instead of blending.Let's compare how these different types of inheritance affect phenotype ratios.While complete dominance gives us a three-to-one ratio, both incomplete dominance and codominance show one-to-two-to-one ratios of their respective phenotypes.