Term | Definition |
allele | one of the alternative forms of a gene that governs a characteristic, such as hair color |
codominance | a condition in which both alleles for a gene are fully expressed |
dihybrid cross | a cross between individuals that have different alleles for the same gene |
dominant | in genetics, describes an allele that is fully expressed whenever the allele is present in an individual |
genetics | the science of heredity and of the mechanisms by which traits are passed from parents to offspring |
genotype | the entire genetic makeup of an organism; also the combination of genes for one or more specific traits |
heredity | the passing of genetic traits from parent to offspring |
homozygous | describes an individual that has identical alleles for a gene on both homologous chromosomes |
heterozygous | describes an individual that has two different alleles of a gene |
incomplete dominance | a condition in which a trait in an individual is intermediate between the phenotype of the individual's two parents because the dominant allele is unable to express itself fully |
monohybrid cross | a cross between individuals that involves one pair of contrasting traits |
phenotype | an organism's appearance or other detectable characteristic that results from the organism's genotype and the environment |
probability | the likelihood that a possible future event will occur in any given instance of the event; the mathematical ratio of the number of times one outcome of any event is likely to occur to the number of possible outcomes of the event |
Punnett Square | a graphic used to predict the results of a genetic cross |
test cross | the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype |
trait | one of two or more possible forms of a characteristic; a recognizable feature or characteristic of an organism |
gene | the most basic physical unit of heredity; a segment of DNA that codes for a functional unit of RNA and/or a protein |
genome | the complete genetic material contained in an individual or species |
recessive | in genetics describes an allele that is expressed only when no dominant allele is present in an individual |
crossing over | exchange of chromosome segments between homologous chromosomes during meiosis I |
carrier | in biology, an individual who has one copy of a recessive autosomal allele that causes disease in the homozygous condition |
sex-linked gene | gene that is located on a sex chromosome |
X chromosome inactiviation | process that occurs in female mammals in which one of the X chromosomes is randomly turned off in each cell |
polygenic trait | a trait that is produced by two or more genes |
somatic cell | cell that makes up all of the body tissues and organs, except gametes |
gamete | a haploid reproductive cell that unites with another haploid reproductive cell to form a zygote |
fertilization | the union of a male and female gamete to from a zygote |
diploid | a cell that contains two haploid sets of chromosomes |
haploid | describes a cell, nucleus, or organism that has only one set of unpaired chromosomes |
meiosis | a process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, which results in the production of sex cells (gametes or spores) |
sperm | the male gamete (sex cell) |
egg | the female gamete (sex cell) |