A practice whereby animal or plant breeders choose which individual animals or plants will be allowed to mate based on the traits (such as coat color or body size) they hope to produce in the offspring. Animals or plants that don't have the desirable traits aren't allowed to breed.
Offspring of parents who differ from each other with regard to certain traits of certain aspects of genetic makeup; heterozygotes.
Principles of segregation
Genes (alleles) occur in pairs because chromosomes occur in pairs. During gamete formation, the members of each pair of alleles separate, so that each gamete contains one member of each pair.
Describing a trait that isn't expressed in heterozygotes; also refers to the allele that governs the trait. For a recessive allele to be expressed, an individual must have two copies of it (i.e., the individual must be homozygous).
In genetics, describing a trait governed by an allele that's expressed in the presence of another allele (i.e., in heterozygotes). Dominant alleles prevent the expression of recessive alleles in heterozygotes. (This is the definition of complete dominance).
Having the same allele at the same locus on both members of a pair of chromosomes.
Having different alleles at the same locus on members of a pair of chromosomes.
The genetic makeup of an individual. Genotype can refer to an organism's entire genetic makeup or to the alleles at a particular locus.
The observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environmental factors.
Principle of independent assortment
The distribution of one pair of alleles into gametes does not influence the distribution of another pair. The genes controlling different traits are inherited independently of one another.
The chance distribution of chromosomes to daughter cells during meiosis. Along with recombination, random assortment is an important source of genetic variation (but not new alleles).
Characteristics that are influenced by alleles at only one genetic locus. Examples include many blood types, such as ABO. Many genetic disorders, including sickle-cell anemia and Tay-Sachs disease are also Mendelian traits.
Large molecules found on the surface of cells. Several different loci govern various antigens on red and white blood cells. (Foreign antigens provoke and immune response).
The expression of two alleles in heterozygotes. In this situation, neither allele is dominant or recessive, so they both influence the phenotype.
A diagram showing family relationships. It's used to trace the hereditary pattern of particular genetic (usually Mendelian) traits.
Referring to traits that are influenced by genes at two or more loci. Examples include stature, skin color, eye color and hair color. Many (but not all) polygenic traits are influenced by environmental factors such as nutrition and exposure to sunlight.
In reference to polygenic inheritance, molecules that influence the color of skin, hair and eyes.
The capacity of a single gene to influence several phenotypic expressions.
In genetics, inherited differences among individuals; the basis of all evolutionary change.
In a population, the percentage of all the alleles at a locus accounted for by one specific allele.
Within a species, a community of individuals where mates are usually found.
All of the genes shared by the reproductive members of a population.
Small changes occurring within a species, such as changes in allele frequencies.
Changes produced only after many generations, such as the appearance of a new species.
Short, adjacent segments of DNA within a gene that are repeated several times.
Exchange of genes between populations.
Evolutionary changes, or changes in allele frequencies, that are produced by random factors in small populations. Genetic drift is a result of small population size.
A type of genetic drift in which allele frequencies are altered in small populations that are taken from, or are remnants of, larger populations.
Sickle Cell Trait
Heterozygous condition where a person has one HbA allele and one HbS allele. Thus they have some normal hemoglobin.