Biology 30: Genetics
progeny
offspring
dominant trait
a characteristic that is expressed when one or both alleles in an individual are the dominant form
recessive trait
a characteristic that is expressed only when both alleles in an individual are the recessive form
allele
one of the alternative forms of a gene
homozygous
having identical alleles from the same gene
heterozygous
having different alleles for the same gene
genotype
the genetic complement of an organism
phenotype
the observable characteristics of an organism
segregation
the separation of alleles during meiosis
phenotypic ratio
the ratio of offspring with a dominant trait to the alternative, recessive trait
genotypic ratio
the ratio of offspring with each possible allele combination from a particular cross
Punnett square
a chart used to determine the predicted outcome of a genetic cross
test cross
the cross of an individual of unknown genotype to an individual that is fully recessive
pedigree chart
a chart that is used to record the transmission of a particular trait or traits over several generations
wild type
the most common allele of a gene with multiple alleles
mutant
any allele of a gene other than the wild type allele
incomplete dominance
the expression of both forms of an allele in a heterozygous individual in the cells of an organism, producing an incomplete phenotype
codominance
the expression of both forms of an allele in a heterozygous individual in different cells of the same organism
dihybrid cross
a genetic cross involving two genes, each of which has more than one allele
selective breeding
the crossing of desired traits from plants and animals to produce offspring with both characteristics
inbreeding
the process whereby breeding stock is drawn from a limited number of individuals possessing desirable phenotypes
polygenic trait
inherited characteristics that are determined by more than one gene
epistatic gene
a gene that makes the expression of another gene or genes
autosome
a chromosome not involved in sex determination
linked genes
genes that are located on the same chromosome
sex-linked trait
trait that is determined by genes located on the sex chromosomes
recessive lethal
a trait that, when both recessive alleles are present, results in death or severe malformation of the offspring; usually, recessive traits occur more frequently in males
Barr body
a small, dark spot of chromatin located in the nucleus of a female mammalian
sex-linked traits
trait that is determined by genes located on the sex chromosomes
linkage group
a group of linked genes on a chromosome
locus (pl. loci)
a specific location along a chromosome where a particular gene is found
marker gene
a gene that confers an easily identifiable phenotype and is used to trace the inheritance of other genes that are difficult to identify; it must be located on the same chromosome, and ideally, at a very small distance from the gene being followed