Variation. Genetics and health

Human genetics studies human heredity and variation. Mendelian crossing is not possible with humans, generations are few and slow, so special methods are used. In the genealogical (pedigree) method the traits of a proband (the person under study) and relatives are followed through many generations to decide whether a trait is dominant or recessive, autosomal or sex-linked. The twin method compares identical (genetically the same) and fraternal twins to assess the contributions of genotype and environment. The cytogenetic method examines the number and structure of chromosomes (karyotype) under a microscope and finds chromosomal and genomic disorders. The biochemical method – analysis of substances in blood and urine – detects metabolic disorders. The population-statistical method calculates allele and genotype frequencies (the Hardy–Weinberg law: p² + 2pq + q² = 1). DNA analysis (the molecular-genetic method) is now widely used too. Medical-genetic counselling helps families assess risk when planning, and newborn screening allows early detection of some diseases.