Biology: Genetics, Reproduction, and Biotechnology - Mendelian Inheritance, Variation, and Genetic Disorders

Mendelian Inheritance: Gregor Mendel's principles explain how traits are passed from parents to offspring. The Law of Segregation states that an individual possesses two alleles for a trait, which separate during gamete formation ($A$ and $a$).

Genotype vs. Phenotype: The Genotype is the genetic constitution of an organism (e.g., $TT$, $Tt$, or $tt$), while the Phenotype is the observable physical characteristic (e.g., Tall or Short).

Dominance and Recessiveness: A dominant allele ($T$) masks the effect of a recessive allele ($t$). For a recessive trait to be expressed, the organism must be homozygous recessive ($tt$).

Homozygous vs. Heterozygous: An organism with two identical alleles is Homozygous ($BB$ or $bb$). An organism with two different alleles is Heterozygous ($Bb$).

Variation: Differences between individuals of the same species. Continuous Variation (e.g., height, weight) is influenced by multiple genes and the environment. Discontinuous Variation (e.g., blood group, ability to roll tongue) is usually controlled by a single gene and falls into distinct categories.

Genetic Disorders: These are caused by DNA mutations. For example, Cystic Fibrosis is an autosomal recessive disorder; an individual must inherit the genotype $ff$ to have the disease. Carriers have the genotype $Ff$.

Biotechnology: Involves using living organisms or biological systems to develop products. Genetic Engineering involves altering the DNA of an organism to produce desired traits, such as insulin-producing bacteria.