What are Dominant and Recessive Traits? Grade 7 Science Explained.

🧬 What are Dominant and Recessive Traits?

In genetics, traits are characteristics or features that are inherited from parents. These traits are determined by genes, which come in pairs called alleles. Alleles can be either dominant or recessive.

📜 A Brief History

The concept of dominant and recessive traits was first introduced by Gregor Mendel in the 19th century. Mendel, through his experiments with pea plants, discovered that certain traits mask the expression of others. His work laid the foundation for modern genetics.

🔬 Key Principles

• 🌱 Genes and Alleles: Genes are segments of DNA that determine specific traits. Alleles are different versions of a gene. For example, a gene for eye color might have an allele for blue eyes and an allele for brown eyes.
• 💪 Dominant Alleles: A dominant allele expresses its trait even when paired with a recessive allele. It "masks" the effect of the recessive allele. We represent dominant alleles with uppercase letters (e.g., 'A').
• Recessive Alleles: A recessive allele only expresses its trait when paired with another recessive allele. If a dominant allele is present, the recessive trait will not show. We represent recessive alleles with lowercase letters (e.g., 'a').
• 🧮 Genotype and Phenotype:
  • Genotype: The genetic makeup of an organism (e.g., AA, Aa, or aa).
  • Phenotype: The observable characteristics or traits of an organism (e.g., brown eyes or blue eyes).
• ➗ Punnett Squares: We use Punnett squares to predict the possible genotypes and phenotypes of offspring based on the genotypes of their parents.

🌍 Real-world Examples

Let's look at some human examples:

• 👁️ Eye Color: Brown eyes (B) are dominant over blue eyes (b). So, if you have at least one 'B' allele (BB or Bb), you'll have brown eyes. You only have blue eyes if you have two 'b' alleles (bb).
• 🧑‍🦱 Hair Curliness: Curly hair (C) is often dominant over straight hair (c). If you have at least one 'C' allele (CC or Cc), you'll likely have curly hair. You only have straight hair if you have two 'c' alleles (cc).
• 👅 Tongue Rolling: The ability to roll your tongue (T) is dominant over the inability to roll your tongue (t). If you have at least one 'T' allele (TT or Tt), you can roll your tongue. You can't roll your tongue only if you have two 't' alleles (tt).

📝 Punnett Square Example

Let's say we have two parents. One parent is heterozygous for brown eyes (Bb) and the other parent is also heterozygous for brown eyes (Bb). Here's the Punnett Square:

From this Punnett Square, we can see that there is a 75% chance of the offspring having brown eyes and a 25% chance of having blue eyes.

🔑 Conclusion

Dominant and recessive traits are fundamental concepts in genetics. They explain how traits are passed down from parents to offspring. Understanding these concepts helps us predict the likelihood of certain traits appearing in future generations. Keep exploring the fascinating world of genetics! 🧬