the genetic makeup responsible for a particular trait
Phenotype
an organism’s observable traits (determined by genotype and environment)
gene
genetic material coding for a single gene product (peptide, rRNA or tRNA)
locus
the chromosomal location of a gene
allele
one variant of a gene
Homologous chromosomes
– chromosomes that code for the same set of genes
- may have different alleles though (one from each parent)
Homozygous
– having two identical alleles for a gene
Heterozygous
– having two different alleles for a gene
wild type
the “normal” or most prevalent allele in a population
dominant
an allele where only one copy is necessary to yield the corresponding phenotype
recessive
an allele where two copies are necessary to yield the corresponding phenotype
complete dominance
when a heterozygote has the phenotype of only 1 of the alleles (the dominant one)
codominance
both inherited alleles are completely expressed (ex. blood types – ABO)
incomplete dominance
– phenotypes of the progeny that are intermediate of the parental phenotypes(snap dragons – homozygous red crossed with homozygous white gives pink progeny)
leakage
when a loss of function mutation doesn’t result in complete lack of a phenotype
Penetrance
the percentage of organisms having a certain genotype expressing a certain phenotype
expressivity
a term describing the variation in phenotype among organisms with a given genotype
Pleiotropism
when a single gene affects multiple traits
Polygenism
when multiple genes affect a single trait
epistasis
when the expression of a gene is dependent upon another gene
gene pool
the set of all alleles in a population
Nondisjunction
– failure of tetrads to separate during meiosis I or sister chromatids in meiosis II
Examples: Down Syndrome (trisomy 21), Turner Syndrome (X),
Kleinfelter Syndrome (XXY)
translocation
movement of a segment of one chromosome to another non-homologous chromosome