Genetics Terminology

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trait

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any characteristic that can be passed from parent to offspring.

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heredity

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passing of traits from parent to offspring.

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Genetics

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study of heredity

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alleles

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two forms of a gene (dominant and recessive)

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dominant allele

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an allele whose trait always shows up in the organism when the allele is present.

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recessive allele

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an allele that is masked when a dominant allele is present.

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genotype

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an organism's genetic makeup, or allele combinations.

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homozygous

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having two identical alleles for a trait.

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heterozygous

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having two different alleles for a trait.

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monohybrid cross

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cross involving a single trait.

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dihybrid cross

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cross involving two traits.

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Punnett Square

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a chart that shows all the possible combinations of alleles that can result from a genetic cross.

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Law of Dominance

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when different alleles for a characteristic are inherited (heterozygous), the trait of only one (the dominant one) will be expressed. The recessive trait's phenotype only appears in true-breeding (homoozygous) individuals.

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Law of Segregation

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states that each genetic trait is produced by a pair of alleles which separate during reproduction.

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Law of Independent Assortment

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states that each factor (gene) is distributed (assorted) randomly and independently of one another in the formation of gametes.

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fertilization

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the process in which an egg cell and a sperm cell join to form a new organism.

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codominance

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a condition in which neither of two alleles of a gene is dominant or recessive.

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carrier

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a person who has one recessive allele for a trait, but does not have the trait.

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chromosome

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a doubled rod of condensed chromatin; contains DNA that carries genetic information.

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clone

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an organism that is genetically identical to the organism from which it was produced.

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DNA

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Deoxyribonucleic acid; the genetic material that carries information about an organism and is passed from parent to offspring.

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gene

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the set of information that controls a trait; a segment of DNA on a chromosome that codes for a specific trait.

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gene therapy

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the insertion of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder.

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genetic engineering

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the transfer of a gene from the DNA of one organism into another organism, in order to produce an organism with desired traits.

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genetic disorder

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an abnormal condition that a person inherits through genes or chromosomes.

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genome

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all of the DNA in one cell of an organism.

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hybrid

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an organism that has two different alleles for a trait; an organism that is heterozygous for a particular trait.

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inbreeding

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a selective breeding method in which two individuals with identical or similar sets of alleles are crossed.

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karotype

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a picture of all the chromosomes in a cell arranged in pairs.

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meiosis

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the process that occurs in the formation of sex cells (sperm and egg) by which the number of chromosomes is reduced by half.

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messenger RNA

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RNA that copies the coded message from DNA in the nucleus and carries the message into the cytoplasm.

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multiple alleles

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three or more forms of a gene that code for a single trait.

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mutation

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a change in a gene or chromosome.

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pedigree

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a chart or "family tree" that tracks which members of a family have a particular trait.

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purebred

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the offsprind of many generations that have the same traits.

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replication

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the process by which a cell makes a copy of the DNA in its nucleus.

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RNA

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Ribonucleic acid; a nucleic acid that plays an important role in the production of proteins.

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selective breeding

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the process of selecting a few organisms with desired traits to serve as parents of the next generation.

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sex chromosomes

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a pair of chromosomes carrying genes that determine whether a person is male or female.

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sex-linked gene

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a gene that is carried on the X or Y chromosome.

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transfer RNA

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RNA in the cytoplasm that carries an amino acid to the ribosomes and adds it to the growing protein chain.