Mendelian Genetics Vocabulary

ABO blood groups
Genetically determined classes of human blood that are based on the presence or absence of carbohydrates A and B on the surface of red blood cells. The ABO blood group phenotypes, also called blood types, are A, B, AB, and O.
achondroplasia
A form of human dwarfism caused by a single dominant allele; the homozygous condition is lethal.
alleles
An alternative form of a gene.
autosome
A chromosome that is not directly involved in determining sex, as opposed to a sex chromosome.
carrier
In human genetics, an individual who is heterozygous at a given genetic locus, with one normal allele and one potentially harmful recessive allele. The heterozygote is phenotypically normal for the character determined by the gene but can pass on the harmful allele to offspring.
chromosome theory of inheritance
A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
codominance
A phenotypic situation in which the two alleles affect the phenotype in separate, distinguishable ways.
cross
The cross-fertilization of two different varieties of an organism or of two different species; also called hybridization.
cross-fertilization
The fusion of sperm and egg derived from two different individuals.
dihybrid cross
An experimental mating of individuals in which the inheritance of two traits is tracked.
dominant allele
In a heterozygote, the allele that is fully expressed in the phenotype.
Duchenne muscular dystrophy
A human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue.
F1 generation
The first filial, or hybrid, offspring in a genetic cross-fertilization.
F2 generation
Offspring resulting from interbreeding of the hybrid F1 generation.
genotype
The genetic makeup of an organism.
hemophilia
A human genetic disease caused by a sex-linked recessive allele, characterized by excessive bleeding following injury.
heterozygous
Having two different alleles for a given genetic character.
homozygous
Having two identical alleles for a given trait
Huntington disease
A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10-20 years after the onset of symptoms.
hybrids
The offspring of two different varieties of plants or animals.
incomplete dominance
A type of inheritance in which F1 hybrids have an appearance that is intermediate between the phenotypes of the parental varieties.
linkage maps
A map of a chromosome showing the relative positions of genes.
linked genes
Genes that are located on the same chromosome
locus
(plural, loci) The particular site where a gene is found on a chromosome. Homologous chromosomes have corresponding gene loci.
monohybrid cross
An experimental mating of individuals in which the inheritance of a single characteristic is tracked.
P generation
The parent individuals from which offspring are derived in studies of inheritance; P stands for parental.
pedigree
A family tree representing the occurrence of heritable traits in parents and offspring across a number of generations.
phenotype
The physical and physiological traits of an organism.
pleiotropy
The ability of a single gene to have multiple effects.
polygenic inheritance
An additive effect of two or more gene loci on a single phenotypic character.
punnett square
A diagram used in the study of inheritance to show the results of random fertilization.
recessive allele
In a heterozygote, the allele that is completely masked in the phenotype.
red-green color blindness
A class of common sex-linked human disorders involving several genes on the X chromosome; characterized by a malfunction of light-sensitive cells in the eyes; affects mostly males but also homozygous females.
rule of multiplication
A rule stating that the probability of a compound event is the product of the separate probabilities of the independent events.
self-fertilize
The fusion of sperm and egg that are produced by the same individual organism.
sex chromosomes
One of the pair of chromosomes responsible for determining the sex of an individual.
sex-linked gene
A gene located on a sex chromosome.
sickle-cell disease
A genetic disorder in which the red blood cells have abnormal hemoglobin molecules and take on an abnormal shape.
testcross
The mating between an individual of unknown genotype for a particular characteristic and an individual that is homozygous recessive for that same characteristic.
true-breeding
Organisms for which sexual reproduction produces offspring with inheritable trait(s) identical to those of the parents. The organisms are homozygous for the characteristic(s) under consideration