Terms
Part I: General geneti cs
Term Definition
Allele One of the different forms of a gene that can exist at a single locus.
Centimorgan See map unit.
(cM)
Chi-square A statistical test used to determine the probability of obtaining observed proportions by
test chance, under a specific hypothesis.
Chloroplast The small genomic component found in the chloroplasts of plants, concerned with
DNA (cpDNA) photosynthesis and other functions taking place within that organelle.
Chromosome A representation of all chromosomes in the genome as lines, marked with the positions of
map genes known from their mutant phenotypes, plus molecular markers. Based on analysis of
recombinant frequency.
Cis In a heterozygote having two mutant sites within a gene or within a gene cluster, the
conformation arrangement A1A2/a1a2.
Codominance A situation in which a heterozygote shows the phenotypic effects of both alleles equally.
Codon A section of RNA (three nucleotides in length) that encodes a single amino acid.
Coefficient of The ratio of the observed number of double recombinants to the expected number.
coincidence
(c.o.c.)
Complementa Production of wild-type phenotype when two full or partial haploid genomes are united in
tion the same cell.
Complementa A test for determining whether two mutations are in different genes (they complement) or
tion test the same gene (they do not complement).
Crossing over The exchange of corresponding chromosome parts between homologs by breakage and
reunion.
Crossover Meiotic product cell with chromosomes that have engaged in a crossover. Meiotic product
product cell with chromosomes that have engaged in a crossover.
Cytoplasmic Segregation in which genetically different daughter cells arise from a progenitor that is a
segregation cytohet.
Dihybrid A double heterozygote such as A/a ⋅ B/b.
Dihybrid A cross between two individuals identically heterozygous at two loci—for example, A B/a b
cross × A B/a b.
Dimorphism A polymorphism with only two forms.
Dioecious A plant species in which male and female organs are on separate plants.
species
Diploid A cell having two chromosome sets or an individual organism having two chromosome sets
in each of its cells.
Dominant The phenotype shown by a heterozygote. Also, an allele that expresses its phenotypic effect
even when heterozygous with a recessive allele; thus, if A is dominant over a, then A/A and
A/a have the same phenotype.
Dominant A mutant allele that in a single dose (a heterozygote) wipes out gene function by a spoiler
negative effect on the protein.
mutation
Double Genotype with mutant alleles of two different genes.
mutants
Epistasis A situation in which the differential phenotypic expression of a genotype at one locus
depends on the genotype at another locus; a mutation that exerts its expression while
1
, canceling the expression of the alleles of another gene.
Essential A gene without at least one copy of which the organism dies.
gene
Expressivity The degree to which a particular genotype is expressed in the phenotype.
First filial The progeny individuals arising from a cross of two homozygous diploid lines.
generation
(F1)
Forward The classical approach to genetic analysis, in which genes are first identified by mutant
genetics alleles and mutant phenotypes and later cloned and subjected to molecular analysis.
Full Describes an allele that expresses itself the same in single copy (heterozygote) as in double
(complete) copy (homozygote).
dominance
Gene The fundamental physical and functional unit of heredity, which carries information from
one generation to the next; a segment of DNA composed of a transcribed region and a
regulatory sequence that makes transcription possible.
Gene The process by which a gene’s DNA sequence is transcribed into RNA and, for protein-
expression coding genes, into a polypeptide.
Genetic The use of recombination and mutation to piece together the various components of a
dissection given biological function.
Genetic map A distance on the chromosome map corresponding to 1 percent recombinant frequency.
unit (m.u.)
Genetics (1) The study of genes. (2) The study of inheritance.
Genomics The cloning and molecular characterization of entire genomes.
Genotype The allelic composition of an individual or of a cell— either of the entire genome or, more
commonly, of a certain gene or a set of genes.
Haploid A cell having one chromosome set or an organism composed of such cells.
Haploinsuffici Describes a gene that, in a diploid cell, is insufficient to promote wild-type function in only
ent one copy (dose).
Haplosufficie Describes a gene that, in a diploid cell, can promote wild-type function in only one copy
nt (dose).
Heteroduplex DNA in which there is one or more mis-matched nucleotide pairs in a gene under study.
DNA
Heterogameti The sex that has heteromorphic sex chromosomes (for example, XY) and hence produces
c sex two different kinds of gametes with respect to the sex chromosomes.
Heterokaryon A culture of cells composed of two different nuclear types in a common cytoplasm.
Heterozygote An individual organism having a heterozygous gene pair.
Heterozygous In diploids, refers to a gene pair consisting of two different alleles of that specific gene—for
example, A/a or A1/A2.
Homogametic The sex with homologous sex chromosomes (for example, XX).
sex
Homozygote An individual organism that is homozygous.
Homozygous Refers to the state of carrying a pair of identical alleles at one locus.
Homozygote Refers to a genotype such as A/A.
dominant
Homozygote Refers to a genotype such as a/a.
recessive
Hybrid vigor A situation in which an F1 is larger or healthier than its two different pure parental lines.
Incomplete A situation in which a heterozygote shows a phenotype quantitatively (but not exactly)
dominance intermediate between the corresponding homozygote phenotypes. (Exact intermediacy
means no dominance.)
2
Part I: General geneti cs
Term Definition
Allele One of the different forms of a gene that can exist at a single locus.
Centimorgan See map unit.
(cM)
Chi-square A statistical test used to determine the probability of obtaining observed proportions by
test chance, under a specific hypothesis.
Chloroplast The small genomic component found in the chloroplasts of plants, concerned with
DNA (cpDNA) photosynthesis and other functions taking place within that organelle.
Chromosome A representation of all chromosomes in the genome as lines, marked with the positions of
map genes known from their mutant phenotypes, plus molecular markers. Based on analysis of
recombinant frequency.
Cis In a heterozygote having two mutant sites within a gene or within a gene cluster, the
conformation arrangement A1A2/a1a2.
Codominance A situation in which a heterozygote shows the phenotypic effects of both alleles equally.
Codon A section of RNA (three nucleotides in length) that encodes a single amino acid.
Coefficient of The ratio of the observed number of double recombinants to the expected number.
coincidence
(c.o.c.)
Complementa Production of wild-type phenotype when two full or partial haploid genomes are united in
tion the same cell.
Complementa A test for determining whether two mutations are in different genes (they complement) or
tion test the same gene (they do not complement).
Crossing over The exchange of corresponding chromosome parts between homologs by breakage and
reunion.
Crossover Meiotic product cell with chromosomes that have engaged in a crossover. Meiotic product
product cell with chromosomes that have engaged in a crossover.
Cytoplasmic Segregation in which genetically different daughter cells arise from a progenitor that is a
segregation cytohet.
Dihybrid A double heterozygote such as A/a ⋅ B/b.
Dihybrid A cross between two individuals identically heterozygous at two loci—for example, A B/a b
cross × A B/a b.
Dimorphism A polymorphism with only two forms.
Dioecious A plant species in which male and female organs are on separate plants.
species
Diploid A cell having two chromosome sets or an individual organism having two chromosome sets
in each of its cells.
Dominant The phenotype shown by a heterozygote. Also, an allele that expresses its phenotypic effect
even when heterozygous with a recessive allele; thus, if A is dominant over a, then A/A and
A/a have the same phenotype.
Dominant A mutant allele that in a single dose (a heterozygote) wipes out gene function by a spoiler
negative effect on the protein.
mutation
Double Genotype with mutant alleles of two different genes.
mutants
Epistasis A situation in which the differential phenotypic expression of a genotype at one locus
depends on the genotype at another locus; a mutation that exerts its expression while
1
, canceling the expression of the alleles of another gene.
Essential A gene without at least one copy of which the organism dies.
gene
Expressivity The degree to which a particular genotype is expressed in the phenotype.
First filial The progeny individuals arising from a cross of two homozygous diploid lines.
generation
(F1)
Forward The classical approach to genetic analysis, in which genes are first identified by mutant
genetics alleles and mutant phenotypes and later cloned and subjected to molecular analysis.
Full Describes an allele that expresses itself the same in single copy (heterozygote) as in double
(complete) copy (homozygote).
dominance
Gene The fundamental physical and functional unit of heredity, which carries information from
one generation to the next; a segment of DNA composed of a transcribed region and a
regulatory sequence that makes transcription possible.
Gene The process by which a gene’s DNA sequence is transcribed into RNA and, for protein-
expression coding genes, into a polypeptide.
Genetic The use of recombination and mutation to piece together the various components of a
dissection given biological function.
Genetic map A distance on the chromosome map corresponding to 1 percent recombinant frequency.
unit (m.u.)
Genetics (1) The study of genes. (2) The study of inheritance.
Genomics The cloning and molecular characterization of entire genomes.
Genotype The allelic composition of an individual or of a cell— either of the entire genome or, more
commonly, of a certain gene or a set of genes.
Haploid A cell having one chromosome set or an organism composed of such cells.
Haploinsuffici Describes a gene that, in a diploid cell, is insufficient to promote wild-type function in only
ent one copy (dose).
Haplosufficie Describes a gene that, in a diploid cell, can promote wild-type function in only one copy
nt (dose).
Heteroduplex DNA in which there is one or more mis-matched nucleotide pairs in a gene under study.
DNA
Heterogameti The sex that has heteromorphic sex chromosomes (for example, XY) and hence produces
c sex two different kinds of gametes with respect to the sex chromosomes.
Heterokaryon A culture of cells composed of two different nuclear types in a common cytoplasm.
Heterozygote An individual organism having a heterozygous gene pair.
Heterozygous In diploids, refers to a gene pair consisting of two different alleles of that specific gene—for
example, A/a or A1/A2.
Homogametic The sex with homologous sex chromosomes (for example, XX).
sex
Homozygote An individual organism that is homozygous.
Homozygous Refers to the state of carrying a pair of identical alleles at one locus.
Homozygote Refers to a genotype such as A/A.
dominant
Homozygote Refers to a genotype such as a/a.
recessive
Hybrid vigor A situation in which an F1 is larger or healthier than its two different pure parental lines.
Incomplete A situation in which a heterozygote shows a phenotype quantitatively (but not exactly)
dominance intermediate between the corresponding homozygote phenotypes. (Exact intermediacy
means no dominance.)
2
