IPA kelas 9 : Pewarisan Sifat II (Persilangan Monohibrid : Hukum 1 Mendel)

Introduction

This tutorial covers the principles of Mendel's first law of inheritance, focusing on monohybrid crosses involving dominant and recessive traits. Understanding these concepts is crucial for students learning genetics, particularly in grade 9. By the end of this guide, you'll grasp the basics of monohybrid crosses and the significance of Mendel's findings.

Step 1: Understand Key Terms

Before diving into monohybrid crosses, familiarize yourself with the following terms:

• Gene: A unit of heredity that is transferred from a parent to offspring and determines some characteristic of the offspring.
• Allele: Different versions of a gene that may produce distinguishable traits.
• Dominant Trait: A trait that appears in the offspring if one of the parents contributes it.
• Recessive Trait: A trait that appears in the offspring only when both alleles are recessive.

Step 2: Familiarize Yourself with Mendel's First Law

Mendel's first law, also known as the Law of Segregation, states that:

• During the formation of gametes, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene.
• This means that offspring inherit one allele from each parent.

Practical Tip

Visualize this concept with a simple Punnett square, which helps to predict the outcome of genetic crosses.

Step 3: Perform a Monohybrid Cross

Here’s how to conduct a monohybrid cross:

1. Select Parent Traits: Choose a trait to study (e.g., flower color). For instance:

   • Dominant allele (T) for tall plants
   • Recessive allele (t) for short plants

2. Identify Parent Genotypes: Determine the genotypes of the parents:

   • Homozygous dominant (TT)
   • Homozygous recessive (tt)

3. Set Up a Punnett Square:

   • Create a 2x2 grid.
   • Place one parent’s alleles on the top and the other’s on the side.

       T   T
      --------
    t | Tt | Tt |
      --------
    t | Tt | Tt |
   

4. Analyze Offspring Genotypes: From the Punnett square, you will see that all offspring (100%) will be Tt (heterozygous).

5. Determine Phenotype Ratios: Since T is dominant, all offspring will exhibit the dominant phenotype (tall).

Step 4: Explore Real-World Applications

Understanding monohybrid crosses has practical applications, such as:

• Predicting traits in agriculture (e.g., crop yield, disease resistance).
• Understanding genetic diseases in humans (e.g., tracking inheritance patterns).

Common Pitfalls to Avoid

• Forgetting that recessive traits only appear when both alleles are recessive.
• Misinterpreting the results of the Punnett square; always double-check your calculations.

Conclusion

By following these steps, you now have a foundational understanding of Mendel's first law of inheritance and how to perform a monohybrid cross. Practice using different traits and cross scenarios to deepen your comprehension. For further learning, explore the related videos on genetics to expand your knowledge on dihybrid crosses and genetic disorders.