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Glossary of Chapter 14 - Mendel and the Gene Idea

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Character
heritable features that vary among individuals
Trait
each variant for a character (such as purple or white flowers)
Hybridization
the mating or crossing of two varieties
Monohybrid cross
the term for a cross that tracks the inheritance of a single character
Alleles
alternative versions of a gene
Law of segregation
the separation of alleles into separate gametes
Homozygous
a term used to describe organisms having a pair of identical alleles for a character
Heterozygous
a term used to describe organisms having two different alleles for a gene
Phenotype
an organism’s appearance
Genotype
an organism’s genetic makeup
Law of independent assortment
the independent segregation of each pair of alleles during gamete formation
Incomplete dominance
a condition in which the F1 hybrids have an appearance somewhere in between the phenotypes of the two parental varieties
Complete dominance
a condition in which the phenotypes of the heterozygote and the dominant homozygote are indistinguishable
Codominance
a condition in which both alleles are separately manifest in the phenotype
Pleiotropy
the ability of a gene to affect an organism in many ways
Epistasis
a condition in which a gene at one locus alters the phenotypic expression of a gene at a second locus
Quantitative characters
genetic characters that vary in the population along a continuum
Polygenic inheritance
an additive effect of two or more genes on a single phenotypic character; converse of pleiotrop
Norm of reaction
the product of a genotype is generally not a rigidly defined phenotype, but a range of phenotypic possibilities over which there may be variation due to environmental influence
Multifactorial characters
a term used to describe characters in which many factors, both genetic and environmental, collectively influence phenotype
Pedigree
a family tree describing the interrelationships of parents and children across generations for a particular trait
Carrier
a person who is phenotypically normal but are heterozygous for a certain disorder and, thus, may transmit the recessive allele to offspring
Cystic fibrosis
the most common lethal genetic disease in the United States; membrane chloride channels are defective or absent in those with both recessive alleles for this trait
Sickle-cell disease
the most common inherited disease among blacks; caused by the substitution of a single amino acid in the hemoglobin protein of red blood cells

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