Patterns of Inheritance & Genetics

allele

Alternative forms of a gene that occupy a specific locus on a specific gene.

autosomal chromosome

In humans, the 22 pairs of chromosomes that are not the sex chromosomes (XX or XY).

autosomal dominant

Pattern of dominant inheritance that corresponds to a gene on one of the 22 autosomal chromosomes.

autosomal recessive

Pattern of recessive inheritance that corresponds to a gene on one of the 22 autosomal chromosomes.

carrier

Heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring.

codominance

Pattern of inheritance that corresponds to the equal, distinct, and simultaneous expression of two different alleles.

dominant

Describes a trait that is expressed both in homozygous and heterozygous form.

dominant lethal

Inheritance pattern in which individuals with one or two copies of a lethal allele do not survive in utero or have a shortened life span.

genotype

Complete genetic makeup of an individual.

heterozygous

Having two different alleles for a given gene.

homozygous

Having two identical alleles for a given gene.

incomplete dominance

Pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes.

karyotype

Systematic arrangement of images of chromosomes into homologous pairs.

mutation

Change in the nucleotide sequence of DNA.

phenotype

Physical or biochemical manifestation of the genotype; expression of the alleles.

Punnett square

Grid used to display all possible combinations of alleles transmitted by parents to offspring and predict the mathematical probability of offspring inheriting a given genotype.

recessive

Describes a trait that is only expressed in homozygous form and is masked in heterozygous form.

recessive lethal

Inheritance pattern in which individuals with two copies of a lethal allele do not survive in utero or have a shortened life span.

sex chromosomes

Pair of chromosomes involved in sex determination; in males, the XY chromosomes; in females, the XX chromosomes.

trait

Variation of an expressed characteristic.

X-linked

Pattern of inheritance in which an allele is carried on the X chromosome of the 23rd pair.

X-linked dominant

Pattern of dominant inheritance that corresponds to a gene on the X chromosome of the 23rd pair.

X-linked recessive

Pattern of recessive inheritance that corresponds to a gene on the X chromosome of the 23rd pair.