Genes are the building blocks of heredity. They help determine our traits and characteristics. Each gene is a piece of DNA, which carries the instructions for life.

Humans have about 20,000 to 25,000 genes, and these are packed into 23 pairs of chromosomes. Chromosomes are found in the nucleus of our cells.

Key Concepts:

1. Structure of DNA:

   • DNA looks like a twisted ladder, called a double helix.
   • It is made up of four types of building blocks, known as nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
   • The order of these bases forms the instructions that each gene carries.

2. Expression of Traits:

   • Genes can influence many traits, like eye color, height, or even how likely someone is to get certain diseases.
   • For example, about half of the differences in height among people can be linked to their genes.

3. Alleles and Variations:

   • Genes can have different versions called alleles. For instance, a gene that decides the color of flower in pea plants can come in a purple version or a white version.
   • A dominant allele, like the one for purple flowers, can hide the effect of a weaker allele, leading to different traits being shown.

4. Genetic Inheritance:

   • We get traits from our parents through the alleles they pass on to us. Usually, a child receives half of their genes from their mother and half from their father.
   • Tools like Punnett squares can help predict the chances of a child inheriting a specific trait based on the parents’ genes.

By understanding how genes shape our traits, we learn more about what makes us unique and how species evolve over time.