chapter 5 definitions

• Allele


  One of various versions of the same gene (at the same locus) distinguished by small differences in its DNA sequence
• Artificial selection


  The breeding of plants and animals to produce desirable traits in successive generations; also known as selective breeding
• Autosomal inheritance


  The passing on of a trait through a gene located on an autosome, a chromosome that is not a sex chromosome
• Autosomal trait


  A trait coded for by a gene on an autosome, a chromosome that is not a sex chromosome; a gene of this kind is called autosomal
• Carrier


  In reference to a genetic disease, a carrier is a healthy, heterozygous organism carrying an allele for a recessive phenotype; the organism may transmit the recessive allele and its associated phenotype to its offspring
• Continuous variation


  Variation in a phenotype characteristic that shows a smooth range; this occurs when a trait is controlled by many genes; when graphed, such variation forms a bell-shaped (normal) curve
• Dihybrid cross


  A cross between two organisms that are heterozygous at two gene loci
• Discontinuous variation


  Variation in a characteristic that shows two or just a few clearly distinct phenotypes
• Dominant


  A phenotype that requires only one copy of its allele for it to be expressed in an individual
• First filial generation (F1)

  The first generation of offspring produced from a cross between two parents (P)
• Gene


  A set of instructions that specifies the structure of a protein
• Genetics


  The study of the mechanisms and patterns of inheritance associated with the transmission of coded chemical instructions from one generation to the next
• Genotype


  The specific combination of alleles for a particular gene locus belonging to an individual or cell
• Heredity


  The study of inheritance; the genetic transmission of characteristics from one generation to the next
• Heterozygous


  A genotype with two different alleles for a single gene locus
• Homozygous

  A genotype with two identical alleles for a single gene locus
• Independent assortment


  Random orientation of maternal and paternal homologous chromosomes at the equator during metaphase 1, resulting in random combinations of alleles in the gametes at the conclusion of meiosis
• Inheritance


  The genetic acquisition of characteristics by offspring from their parents
• Linked genes


  Genes or alleles that are inherited together more frequently because they are located near one another on the same chromosome
• Monohybrid

  An organism that is heterozygous with respect to a single gene
• Monohybrid cross


  A cross between two monohybrids (see monohybrid); only one gene is involved, and the cross is between two organisms that are heterozygous at one gene locus for a dominant and a recessive allele
• Multiple alleles


  The term given when three or more alleles
• Monohybrid cross


  A cross between two monohybrids; only one gene is involved, and the cross is between two organisms that are heterozygous at one gene locus for a dominant and a recessive allele
• Multiple alleles


  Three or more alleles of a gene exist among members of a population
• Non-homologous chromosomes


  Chromosomes that do not belong to the same pair; they contain different sets of genes
• Parental generation (P)


  Two individuals or lines that represent the start of a breeding experiment; their offspring are the F1 generation
• Phenotype


  The actual form taken by a specific feature in a particular individual, based on their genotype and influenced by the environment; it can be used in reference to particular traits or characteristics, or to the overall form of an individual
• Polygene


  A gene whose alleles have a small, additive effect on a phenotype; many polygenes together contribute to continuous variation in a phenotype
• Polygenic inheritance


  Transmission between generations of characteristics that are controlled by polygenes
• Pure-breeding


  A line of organisms that always produce offspring with the same phenotype when crossed with one another
• Recessive

  A phenotype that requires two copies of its allele in an individual in order to be expressed
• Second filial generation (F2)

  Offspring of the F1 generation; the second generation produced from a cross between two homozygous parents (P)
• Selective breeding


  A process by which humans domesticate animals or plants by purposely choosing individuals with the most desirable characteristics as parents for each successive generation of breeding
• Sex-linked


  Describes a gene located on a sex chromosome
• Sex-linked trait


  A trait inherited on a sex chromosome; the gene of interest on a sex chromosome is described as sex-linked
• Test cross


  A technique used by geneticists in which an individual whose genotype is unknown for a dominant phenotype is crossed with an individual that is homozygous recessive at the locus in question
• Trait

  An inheritable characteristic; phenotype