Genetic Variation

DNA and Genes

• DNA: Unique blueprint mapping physical traits.
• Genes: Segments of DNA responsible for specific functions.

Heredity and Genetics

• Heredity: Passing of traits from parents to offspring.
• Genetics: The science that studies heredity.

Heritable vs. Non-Heritable Characteristics

• Heritable: Traits passed from one generation to the next (e.g., eye, hair, skin color).
• Non-Heritable: Traits acquired through life (e.g., playing an instrument, scars).

Types of Heritable Characteristics

• Continuous Variation: Range of possibilities (e.g., height, mass, hair color).
• Discrete Variation: Either/or form (e.g., blood type, biological sex, tongue curling).

Environmental Variation

• Traits affected by the environment.
• Malnutrition affecting height, plant health based on environment.

Why Only Some Traits Are Passed On?

• Offspring receive half of their genes from each parent.
• Genes are broken into two alleles.
• People generally have two alleles for each gene.

Dominant vs. Recessive Traits

• Dominant: Always show up in offspring (uppercase letter, e.g., $B$ for brown hair).
• Recessive: Only show up if no dominant trait is present (lowercase letter, e.g., $b$ for blonde hair).

Examples of Dominant and Recessive Traits

• Dark hair (Dominant: $LL$ or $Ll$) vs. Light hair (Recessive: $ll$).
• Curly hair (Dominant: $TT$ or $Tt$) vs. Straight hair (Recessive: $tt$).
• Tongue curling (Dominant: $CC$ or $Cc$) vs. No tongue curling (Recessive: $cc$).

Homozygous vs. Heterozygous

• Homozygous: Two identical alleles (e.g., $BB$ or $bb$).
• Heterozygous: One dominant and one recessive allele (e.g., $Bb$).

Phenotype vs. Genotype

• Phenotype: What visibly shows up in offspring (e.g., brown hair).
• Genotype: Genetic characteristics of offspring (e.g., $Bb$ or $BB$).