using a punnet square, explain how Mendel's principles of dominance and recessiveness can be observed in a monohybrid cross involving two heterozygous plants
Answer (1)
Mendel's principles of dominance and recessiveness are clearly illustrated in aswer monohybrid cross of two heterozygous plants using a Punnett Square. Let's assume we're crossing pea plants where the allele for tallness (T) is dominant over the allele for shortness (t). Both parent plants are heterozygous, meaning they have one dominant (T) and one recessive (t) allele (Tt). 1. Setting up the Punnett Square: We represent the alleles of each parent along the top and side of the square: 2. Determining the Offspring Genotypes: By combining the alleles from each parent, we get the genotypes of the offspring: - TT: Homozygous dominant – These plants will be tall.- Tt: Heterozygous – These plants will also be tall (because tallness, T, is dominant).- tt: Homozygous recessive – These plants will be short (because they have two recessive alleles). 3. Observing Mendel's Principles: - Principle of Dominance: The Punnett Square shows that the tall phenotype (physical characteristic) appears more frequently than the short phenotype. This demonstrates dominance; the dominant allele (T) masks the expression of the recessive allele (t) in heterozygotes (Tt).- Principle of Segregation: Each parent contributes only one allele (either T or t) to each offspring. This is shown by the way we combine the parental alleles in the Punnett Square. The alleles separate during gamete (sex cell) formation, and then randomly recombine during fertilization. 4. Phenotypic and Genotypic Ratios: From the Punnett Square, we can calculate the phenotypic and genotypic ratios: - Genotypic Ratio: 1 TT : 2 Tt : 1 tt (1:2:1)- Phenotypic Ratio: 3 Tall : 1 Short (3:1) The 3:1 phenotypic ratio is a classic Mendelian ratio observed in monohybrid crosses involving one gene with two alleles, where one allele is completely dominant over the other. The Punnett Square provides a visual and straightforward method to predict the probability of each genotype and phenotype in the offspring.
