Genotype

A genotype is the complete set of genetic material (DNA/genes) an organism carries, representing its specific genetic makeup. It’s the sequence of alleles (variants of a gene) inherited from parents, which influences traits. Here’s a breakdown:

Key Concepts:

1. Alleles:
   Different versions of a gene (e.g., allele for brown eyes vs. blue eyes).

• Homozygous: Two identical alleles (e.g., AA or aa).
• Heterozygous: Two different alleles (e.g., Aa).

1. Genotype vs. Phenotype:

• Genotype: Genetic code (e.g., Bb for a plant height gene).
• Phenotype: Observable trait (e.g., “tall” due to B being dominant).

1. Notation:
   Genotypes are represented by letters:

• Capital letter = Dominant allele (e.g., T for tall).
• Lowercase letter = Recessive allele (e.g., t for short).
• Example: TT (tall), Tt (tall), tt (short).

1. Genetic Inheritance:

• Offspring inherit one allele from each parent.
• Punnett squares predict genotype probabilities (e.g., crossing Tt x Tt → 25% TT, 50% Tt, 25% tt).

Examples:

Trait	Possible Genotypes	Resulting Phenotype
Pea Plant Height	TT or Tt	Tall
	tt	Short
Human Blood Type	IAIA or IAi	Type A
	IBIB or IBi	Type B
	IAIB	Type AB
	ii	Type O

Why Genotypes Matter:

• Disease Risk: Genotypes like BRCA1 mutations increase cancer susceptibility.
• Agriculture: Selecting crop genotypes for drought resistance.
• Evolution: Genetic variation (genotype diversity) drives natural selection.
• Personalized Medicine: Tailoring treatments based on genetic makeup (e.g., pharmacogenomics).

Important Note:

Genotypes interact with the environment to produce phenotypes. For example:

• A plant with “tall” genes (TT) may still be stunted if grown without light.
• Identical twins (same genotype) can have different health outcomes due to lifestyle.

Understanding genotypes helps decode heredity, evolution, and the molecular basis of life! 🧬