Autosomal genes
have two copies of each gene located on an autosome
carrier
an organism that has inherited an allele for a recessive genetic trait but usually does not display that trait or show symptoms of the disease
codominance
the relationship between two alleles of a gene such that a heterozygous organism shows the expression of both alleles in its phenotype
dihybrid cross
a cross in which alleles of two different genes are involved
dominant
a trait that is expressed in the heterozygous condition; also a trait that requires only a single copy of the responsible allele for its phenotypic expression
environment
the external conditions (both biotic and abiotic factors) that surround and affect an organism
epigenetic factors
external factors which change genes, but not the base DNA sequence
epigenetic inheritance
the inheritance of epigenetic tags across generations
epigenetics
the study of changes in organisms caused by modifications of gene expression rather than alteration of the genetic code itself
genotype
the genetic make-up of an organism at one particular gene locus
hemizygous
One allele is present for a gene located on a sex chromosome. This occurs in males, who have only one X or Y chromosome,
heterozygous
a genotype at la particular gene comprising of two different alleles; for example, Aa
homozygous
a genotype at a particular gene comprising of two identical alleles; for example, AA or aa
incomplete dominance
the appearance in a heterozygote of a trait that is intermediate between either of the trait’s homozygous phenotypes
methylation
the addition of a methyl group (–CH3) to a cytosine base of DNA, usually to repress gene transcription
methyl group
a group of one carbon atom bonded to three hydrogen atoms (–CH3)
monohybrid cross
a cross in which alleles of only one gene are involved
phenotype
an observable or measurable characteristic of an organism that is the product of genetic and environmental factors
recessive
a trait that is not expressed but remains hidden or masked in a heterozygous organism
