Explain Mendel’s Monohybrid Cross. Give an example.
Hint: A monohybrid cross refers to a genetic experiment where fertilization occurs between two homozygous parents that differ in only one contrasting characteristic being studied. The offspring resulting from this cross are known as monohybrids. This type of cross was first carried out by Gregor Mendel, who studied the inheritance patterns, earning him the title “Father of Genetics.”
Complete answer:
In his experiments, Mendel conducted seven types of monohybrid crosses, each focusing on a single feature with contrasting traits. He used garden pea plants for his studies. The seven characteristics Mendel examined, with their contrasting traits, included:
- Seed color (Yellow or Green)
- Seed shape (Round or Wrinkled)
- Pod form (Inflated or Constricted)
- Pod color (Green or Yellow)
- Flower color (Purple or White)
- Flower location (Axial or Terminal)
- Plant height (Tall or Dwarf)
For instance, pea color and pea shape are characteristics, while yellow or green, and round or wrinkled are the traits associated with them.
Example of a monohybrid cross:
Mendel began his work by crossing two garden pea plants that differed in height. One was a tall plant, and the other was short (dwarf). Both plants were homozygous—one tall plant had the genotype TT, and the dwarf plant had the genotype tt. When these two plants were crossed, the resulting offspring (called the F1 generation, or first filial generation) were all hybrids or heterozygous plants with the genotype Tt. Even though these plants were genetically mixed (heterozygous), they all displayed the tall phenotype, meaning they looked tall outwardly.
Note: A monohybrid cross involves crossing two pure homozygous parents that differ by only one contrasting characteristic. Gregor Mendel was the first to carry out monohybrid cross experiments using garden pea plants. He noted that the offspring generated in the F1 generation after a monohybrid cross between two pure homozygous parents were heterozygous.