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ABO blood typing
Method of identifying which self-recognition proteins of types A and B are at the surface of an individual�s red blood cells; the absence of either type is designated O.
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alleles
One of two or more molecular forms of a gene at a given locus; alleles arise by mutation and encode slightly different versions of the same trait.
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codominance
A condition in which a pair of nonidentical alleles that influence two different phenotypes are expressed at the same time in heterozygotes.
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continuous variation
Of individuals of a population, a range of small differences in the phenotypic expression of a trait.
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dihybrid cross
Type of experiment that starts with a cross between two truebreeding, homozygous parents that differ in two traits governed by alleles of two genes. The actual experiment is a cross between two of their F1 offspring that are identically heterozygous for alleles of the two genes; e.g., AaBb x AaBb.
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dominant allele
Of diploid cells, an allele that masks the phenotypic effect of any recessive allele paired with it.
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epistasis
An interaction among products of two or more gene pairs that influence the same trait.
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genes
Unit of heritable information in DNA, transmissable from parents to offspring.
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genotype
Genetic makeup of an individual; a single gene pair or the sum total of an individual�s genes.
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homozygous dominant
Having a pair of dominant alleles at a gene locus on homologous chromosomes; e.g., AA.
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homozygous recessive
Having a pair of recessive alleles at a gene locus on homologous chromosomes; e.g., Aa.
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hybrids
Individual having a nonidentical pair of alleles for a trait being studied.
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incomplete dominance
Condition in which one allele of a pair is not fully dominant; the heterozygous phenotype is somewhere between both homozygous phenotypes.
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linkage group
All genes on a chromosome.
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melanin
- A brownish-black pigment.
- monohybrid cross
- An experiment that starts with a cross between two truebreeding, homozygous parents that differ in a trait governed by alleles of one gene. The experiment is a cross between two F1 offspring that are identically heterozygous for the two genes; e.g., Aa x Aa.
- multiple allele system
- Three or more slightly different molecular forms of a gene that persists among the individuals of a population.
- mutation
- [L. mutatus, a change, + -ion, act, result, or process] Heritable change in DNA�s molecular structure. Original source of new alleles and life�s diversity.
- P, F1, F2
- The first and second generation offspring of experimental crosses.
- phenotype
- [Gk. phainein, to show + typos, image] Observable trait or traits of an individual.
- pleiotropy
- A case of alleles at a single gene locus having positive or negative impact on two or more traits.
- polygenic inheritance
- Inheritance of multiple genes that affect the same trait.
- probability
- The odds that each outcome of an event will occur is proportional to the total number of ways in which that outcome can be reached.
- Punnett-square method
- A simple way to predict the probable outcomes of a genetic cross by constructing and filling in a diagram of all possible combinations of genotypes, phenotypes, or both.
- recessive allele
- Allele whose expression in heterozygotes is fully or partially masked by expression of a dominant partner allele. It is fully expressed only in homozygous recessives.
- testcross
- A cross that might reveal the (unknown) genotype of an individual showing dominance for a trait; the individual is crossed with a known homozygous recessive individual.
- true-breeding lineage
- A group consisting of parents and their offspring in which only one version of a trait persists over time.
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