DNA and Genetics Vocabulary Vocabulary Word Definition DNA Deoxyribonucleic acid Hereditary material that controls all the activities of the cell The structure of DNA. DNA is composed of two strands of Double Helix nucleotides, which form bonds with each other as rungs in a ladder. These linked strands then twist around one another to make a helix structure (like a twisted ladder). Genes Segments of DNA that carry hereditary instructions and are passed from parent to offspring Alleles Different forms of a single gene. A human genotype often has 2 alleles for each trait. Dominant trait The trait observed when at least one dominant allele for a characteristic is inherited Recessive trait A trait that is apparent only when two recessive alleles for the same characteristic is inherited Hereditary Traits that are inherited from a parent by an offspring Genotype The inherited combination of alleles (genes). Phenotype An organism’s inherited physical appearance, depending on the genotype. Homozygous A “purebred” genotype in which the organism has two of the same alleles for a particular trait. For example, if you have two brown- eye genes and no blue eye genes. DNA and Genetics Vocabulary Heterozygous A “hybrid” genotype, in which an organism carries two different alleles for the same trait. For example, if you have brown eyes, but also carry a blue-eyed gene, then you are heterozygous for eye color. Mutation A change in the order of bases in an organism’s DNA; deletion, insertion or substitution. Can happen spontaneously or can be due to a mutagen. Can be harmful, helpful, or have no effect on the phenotype. Mutagen Anything that can damage or cause changes in DNA nucleotide A subunit of DNA consisting of a sugar, a phosphate, and one of the four nitrogen bases. Nitrogen Bases Adenine, thymine, cytosine, and guanine (A-T, C-G). These four bases make up the DNA “alphabet” and the order of these bases in the DNA determines the characteristics of the organism. Co-Dominance Occurs when both alleles show through to contribute to the phenotype Incomplete Dominance Occurs when one allele is not completely dominant over the other allele, the result is a mixture between the two alleles Genetic Engineering The manipulation of genes that allows scientists to put genes from one organism into another organism Selective Breeding The breeding of organisms that have a certain desired trait Pedigree A diagram of family history used for tracing a trait through several generations DNA and Genetics Vocabulary .