Campbell Biology in Focus Chapter 11

character

an observable heritable feature that may vary among individuals

trait

one of two or more detectable variants in a genetic character

true-breeding

referring to organisms that produce offspring of the same variety over many generations of self-pollination

hybridization

the mating

P generation

the true-breeding parent individuals from which F₁ hybrid offspring are derived in studies of inheritance; P\= "parental"

F₁ generation

the first filial

F₂ generation

the offspring resulting from interbreeding (self-pollination) of the hybrid (heterozygous) F₁ generation

allele

any of the alternative versions of a gene that may produce distinguishable phenotypic effects

dominant allele

an allele that is fully expressed in the phenotype of a heterozygote

recessive allele

an allele whose phenotypic effect is not observed in heterozygote

law of segregation

states that the two alleles in a pair segregate into different gametes during gamete formation

Punnett square

a diagram used in the studies of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype

homozygous

having two identical alleles for a given gene

heterozygous

having two different alleles for a given gene

phenotype

the observable physical and physiological traits of an organism

genotype

the genetic makeup

testcross

breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype

monohybrid

an organism that is heterozygous with respect to a single gene of interest

monohybrid cross

a cross between two organisms that are heterozygous for the character being followed

dihybrid

An organism that is heterozygous with respect to two genes of interest

dihybrid cross

a cross between two organisms that are each heterozygous for both of the characters being followed

law of independent assortment

states that each pair of alleles segregates independently of each other pair during gamete formation

multiplication rule

a rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities

addition rule

a rule probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities

complete dominance

the situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable

incomplete dominance

the situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele

codominance

the situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate

Tay-Sachs disease

a human genetic disease caused by a recessive allele for a dysfunctional enzyme

pleiotrophy

the ability of a single gene to have multiple effects

epistasis

a type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene

quantitative characters

a heritable feature that varies continuously over a range rather than in an either-or fashion

polygenic inhertance

an additive effect of two or more genes on a single phenotypic character

multifactoral

referring to a phenotypic character that is influenced by multiple genes and environmental factors

pedigree

a diagram of a family tree with conventional symbols

carrier

an individual who is heterozygous at a given genetic locus for a recessively inherited disorder

cystic fibrosis

a human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by an excessive secretion of mucus and consequent vulnerability to infection

sickle-cell disease

a recessively inherited human blood disorder in which a single nucleotide change in a gene causes hemoglobin to aggregate

Huntington's disease

a human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system

multiple allele system

three or more slight different molecular forms of a gene that occur among individuals of a population

continuous variation

a more or less continuous range of small differences in a given trait among its individuals