Inheritance

Inheritance is the transmission of genetic characters from parents to offspring. The fundamental unit of inheritance is the gene, which is a specific sequence of DNA located on chromosomes that determines a particular trait. Different alternative forms of a gene are called alleles. A student must clearly understand the distinction between a genotype (the genetic makeup of an organism, such as $TT$, $Tt$, or $tt$) and a phenotype (the physical or observable expression of that trait, such as tall or dwarf). Traits are typically categorized as either dominant alleles (which mask the expression of other alleles and are represented by capital letters) or recessive alleles (which remain masked in the presence of a dominant allele and are represented by lowercase letters).

Gregor Mendel’s foundational work on garden peas laid the groundwork for modern genetics. Students frequently encounter numerical and conceptual questions based on Mendel's Law of Segregation and Mendel's Law of Independent Assortment. The Law of Segregation states that allele pairs separate during gamete formation, and randomly unite at fertilization. The Law of Independent Assortment states that allele pairs separate independently during the formation of gametes. To solve board exam problems—especially monohybrid and dihybrid crosses—you must master how to construct and interpret Punnett squares to determine expected genotypic and phenotypic ratios (such as the classic $3:1$ phenotypic ratio in monohybrid crosses and $9:3:3:1$ in dihybrid crosses).

Beyond strict Mendelian genetics, board exams frequently test deviations and related chromosomal concepts. Codominance (where both alleles are fully expressed, like the AB blood group) and incomplete dominance (where neither allele is completely dominant, resulting in a blended intermediate phenotype) are high-yield short-answer topics. Additionally, students must know the chromosomal basis of sex determination in humans (XX for females, XY for males) and be familiar with genetic disorders like Down syndrome, Hemophilia, and Color blindness. Be sure to memorize key definitions such as homozygous (identical alleles) and heterozygous (different alleles), as these are standard 2-mark questions in paper sections.