Key Terms – Genetics
- allele
- one of two or more variants of a gene that determines a particular trait for a characteristic
- autosome
- non-sex chromosomes
- codominance
- in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
- continuous variation
- a variation in a characteristic in which individuals show a range of traits with small differences between them
- dihybrid
- the result of a cross between two true-breeding parents that express different traits for two characteristics
- discontinuous variation
- a variation in a characteristic in which individuals show two, or a few, traits with large differences between them
- dominant
- describes a trait that masks the expression of another trait when both versions of the gene are present in an individual
- epistasis
- an interaction between genes such that one gene masks or interferes with the expression of another
- F1
- the first filial generation in a cross; the offspring of the parental generation
- F2
- the second filial generation produced when F1 individuals are self-crossed or fertilized with each other
- genotype
- the underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism
- hemizygous
- the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant
- heterozygous
- having two different alleles for a given gene on the homologous chromosomes
- homozygous
- having two identical alleles for a given gene on the homologous chromosomes
- hybridization
- the process of mating two individuals that differ, with the goal of achieving a certain characteristic in their offspring
- incomplete dominance
- in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
- law of dominance
- in a heterozygote, one trait will conceal the presence of another trait for the same characteristic
- law of independent assortment
- genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur
- law of segregation
- paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors
- linkage
- a phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together
- model system
- a species or biological system used to study a specific biological phenomenon to gain understanding that will be applied to other species
- monohybrid
- the result of a cross between two true-breeding parents that express different traits for only one characteristic
- parental generation (P)
- the first generation in a cross
- phenotype
- the observable traits expressed by an organism
- Punnett square
- a visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid
- recessive
- describes a trait whose expression is masked by another trait when the alleles for both traits are present in an individual
- reciprocal cross
- a paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross
- recombination
- the process during meiosis in which homologous chromosomes exchange linear segments of genetic material, thereby dramatically increasing genetic variation in the offspring and separating linked genes
- test cross
- a cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait
- trait
- a variation in an inherited characteristic
- wild type
- the most commonly occurring genotype or phenotype for a given characteristic found in a population
- X-linked
- a gene present on the X chromosome, but not the Y chromosome