Landmarc Scientific Concept: Genes, Alleles, Dominant and Recessive

 Alleles:

- Alleles are different versions of a gene. Each gene in an organism's DNA exists in pairs, one inherited from each parent.

Dominant and recessive alleles are key concepts in genetics that explain how traits are inherited from one generation to the next.

 Dominant Alleles:

- A dominant allele is one that will express its trait in an organism, even if only one copy (from one parent) is present.

- Dominant alleles are typically represented by a capital letter (e.g., A).

- For example, if the allele for brown eyes (B) is dominant over the allele for blue eyes (b), an individual with either BB or Bb genotype will have brown eyes.

 Recessive Alleles:

- A recessive allele only expresses its trait when two copies are present, meaning the organism must inherit the recessive allele from both parents.

- Recessive alleles are represented by a lowercase letter (e.g., a).

- In the eye color example, an individual would need to have the genotype bb to have blue eyes because the brown eye allele (B) is dominant.

 Homozygous vs. Heterozygous:

- Homozygous: When both alleles for a trait are the same (e.g., BB or bb), the individual is homozygous for that trait.

- Heterozygous: When the alleles for a trait are different (e.g., Bb), the individual is heterozygous. In this case, the dominant allele's trait will be expressed.

 Examples:

1. Huntington's Disease: This is caused by a dominant allele. If a person has one allele for the disease (Hh), they will develop the disease.

2. Cystic Fibrosis: This is caused by a recessive allele. A person must inherit two copies of the cystic fibrosis allele (cc) to have the disease.

Understanding dominant and recessive alleles helps explain the patterns of inheritance for various traits and conditions in living organisms.