| Term | Definition |
|---|
| heredity | The passing of traits from parents to offspring. |
| genetics | The branch of biology that studies heredity. |
| monohybrid cross | A cross that involves one pair of contrasting traits. |
| true breeding | Refers to organisms for which sexual reproduction produces offspring with inherited traits identical to those of the parents; the organisms are homozygous for the characteristics under consideration. |
| alleles | Alternative versions of a gene. |
| law of dominance | One form of a hereditary trait prevents the recessive trait from showing up. |
| homozygous | Two alleles of a particular gene present in an individual are the same. |
| heterozygous | The alleles of a particular gene present in an individual are different. |
| genotype | The set of allleles that an individual has; an individual's genetic make-up. |
| phenotype | The physical appearance of a trait. |
| law of segregation | The two alleles for a trait separate when gametes are formed; explained by the fact that alleles for a trait are on homologous chromosomes, which separate during meiosis. |
| law of independent assortment | The alleles of different genes separate independently of on another during gamete formation; only applies to genes on different chromosomes or those that are far apart on the same chromosome. |
| dihybrid cross | A cross that considers two pairs of contrasting traits. |
| homozygous recessive | Describes an individual with two recessive alleles for a trait; for instance, a pea plant with "pp," resulting in white flowers. |
| heterozygous | Describes an individual with a copy of the dominant and recessive alleles for a trait; for instance, a pea plant with "Pp," resulting in purple flowers. |
| homozygous dominant | Describes an individual with two dominant alleles for a trait; for instance, a pea plant with "PP," resulting in purple flowers. |
| Punnett Square | A diagram used to predict the expected outcomes of a genetic cross. |
| Dihybrid Cross | A cross that involves two pairs of contrasting traits. |
| test cross | A cross in which an individual whose phenotype is dominant, but whose genotype is not known, is crossed with a homozygous recessive individual. |
| polygenic trait | A trait influenced by several genes; the genes may be scattered along the same chromosome or located on different chromosomes. |
| incomplete dominance | When an individual displays a trait that is intermediate between the two parents; causes an intermediate phenotype. |
| codominance | When two dominant alleles are expressed at the same time; Roan coats in horses is an example. |
| multiple alleles | Genes with three or more alleles; The ABO blood groups is an example. |
| pedigree | A family history that shows how a trait is inherited over several generations. |
| carriers | Individuals who are heterozygous for an inherited disorder but do not show symptoms. |
| autosome | A chromosome other than an X or Y chromosome. |
| sex-linked trait | A trait whose allele is located on the X chromosome; most of these traits are recessive; males exhibit these traits more often than females. |
| mutation | A change in genetic material. |
| genetic disorder | Harmful effects produced by inherited mutations. |
| sickle cell anemia | A defective form of hemoglobin causes many red blood cells to bend into a sickle shape; individuals who are heterozygous for this condition may have some protection against malaria. |
| hemophilia | A condition that impairs the blood's ability to clot; caused by a sex-linked recessive allele. |
| huntington's disease | A genetic condition characterized by loss of muscle control, uncontrollable spasms, severe mental illness, and eventually death; caused by an autosomal dominant allele. |
| cystic fibrosis | Most common genetic disorder among caucasians; 1 out of 22 caucasians are carriers. |
| phenylketonuria | The body cannot metabolize the amino acid phenylalanine, which builds up in the blood and body tissue; a recessive genetic disorder. |
| Duchenne Muscular Dystrophy | X-linked genetic disorder; lack of dystrophin causes muscle cells to die. |
| genetic counseling | A form of medical guidance that informs people about genetic problems that could affect them or their offspring. |
| P-generation | The first set of parents crossed in which their genotype is the basis for predicting the genotype of their offspring. |
| F-1 generation | The first generation of offspring which results after mating or genetically crossing two types of parents with different genotypes or phenotypes. |
| F-2 generation | The second filial generation; the offspring of the F-1 generation when the F-1 generation is selfpollinated or when two individuals from the F-1 generation are crossed. |
| hemizygous | Describes an individual who has only one member of a chromosome pair rather than the usual two; refers in particular to X-linked genes in males who under usual circumstances have only one X chromosome. |
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