Chapter 10. Genetics and Heredity

DNA (deoxyribonucleic acid) stores genetic information as a double helix, described by Watson and Crick in 1953. Its four bases pair as A with T and G with C [10][14].

Central dogma: DNA is transcribed into RNA, which is translated into protein. Genes are segments of DNA that code for proteins or functional RNA.

Mendelian genetics. Mendel’s pea experiments showed that traits are inherited as discrete units (genes) with different versions (alleles). A dominant allele is expressed when present; a recessive allele is expressed only when two copies are present. Genotype is the genetic makeup; phenotype is the observable trait [10][11].

Punnett squares predict offspring ratios. A cross of two heterozygotes (Aa × Aa) gives genotypes in a 1 AA : 2 Aa : 1 aa ratio and a 3 : 1 dominant-to-recessive phenotype ratio.

Mutations are changes in DNA. They can be harmless, harmful or beneficial, and are a source of new variation.

Applications and ethics. Genetic testing, gene therapy, genetically modified crops and gene editing raise important questions about safety, fairness and consent.

Review: If one parent is Aa and the other is aa, what fraction of offspring are expected to be aa? (Answer: one half.)