Medelian Biology and Non-Mendelian Genetics

• Gene


  Unit of heredity that carries information for a trait
• Allele


  Different versions of a gene that code for variations of a trait
• Alleles for hair color


  • black
  • brown
  • blond
  • red
• Homozygous


  Having two identical alleles for a gene
• Heterozygous


  Having two different alleles for a gene
• Genotype


  The genetic makeup of an individual (combination of alleles)
• Phenotype


  The observable physical or biochemical characteristics of an organism
• Dominant Allele


  An allele that masks the effect of the recessive allele in a heterozygous individual
• Recessive Allele


  An allele that is masked by the dominant allele in a heterozygous individual
• Law of Segregation


  During gamete formation, alleles for each gene segregate from each other so that each gamete carries only one allele for each gene
• Law of Independent Assortment


  Different traits segregate independently during the formation of gametes
• Law of Dominance


  Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele
• Sex Chromosomes


  Chromosomes that determine the sex of an organism (X and Y in mammals)
• Sex-Linked Genes


  Genes located on the sex chromosomes, with X-linked genes being more common
• Recombination (Crossover)


  The exchange of genetic material between homologous chromosomes during meiosis, which can lead to new combinations of alleles in offspring
• Incomplete Dominance


  Both alleles for a trait are partially expressed, resulting in a blended phenotype in the offspring
• Codominance


  A gene can have more than two possible alleles (versions), leading to more complex inheritance patterns
• Multiple Alleles


  A gene can have more than two possible alleles (versions), leading to more complex inheritance patterns
• Polygenic Inheritance


  Many genes influence a single trait, resulting in a wide range of phenotypes
• Epistasis


  One gene affects the expression of another gene, creating unexpected phenotypic combinations
• Pleiotropy


  A single gene influences multiple seemingly unrelated traits