Chapter 11.txt

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.

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.

A condition in which a pair of nonidentical alleles that influence two different phenotypes are expressed at the same time in heterozygotes.

Of individuals of a population, a range of small differences in the phenotypic expression of a trait.

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.

Of diploid cells, an allele that masks the phenotypic effect of any recessive allele paired with it.

An interaction among products of two or more gene pairs that influence the same trait.

Unit of heritable information in DNA, transmissable from parents to offspring.

Genetic makeup of an individual; a single gene pair or the sum total of an individual�s genes.

Having a pair of dominant alleles at a gene locus on homologous chromosomes; e.g., AA.

Having a pair of recessive alleles at a gene locus on homologous chromosomes; e.g., Aa.

Individual having a nonidentical pair of alleles for a trait being studied.

Condition in which one allele of a pair is not fully dominant; the heterozygous phenotype is somewhere between both homozygous phenotypes.

All genes on a chromosome.

• 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.