Chapter 9 Definitions Flashcards
Effects from alleles of multiple genes that all contribute to the ultimate phenotype for a given characteristic.
additive effects
Alternative versions of a gene.
allele
In genetics, an individual who carries one allele for a recessive trait and does not exhibit the trait; if two carriers mate, they may produce offspring that do exhibit the trait.
carrier
The case in which a heterozygote displays characteristics of both alleles.
codominance
The breeding of organisms that differ in one or more traits.
cross
An individual that is heterozygous at two genetic loci.
dihybrid
A cross between two individuals that are heterozygous for the same two genetic loci.
dihybrid cross
In genetics, describes an allele that masks the phenotypic effect of the other, recessive allele for a trait. The phenotype shows the effect of the dominant allele in both homozygous and heterozygous genotypes.
dominant
The genes that an organism carries for a particular trait; also, collectively, an organism’s genetic composition.
genotype
The greater resemblance of offspring to their parents than to other individuals in the population, a consequence of the passing of characteristics from parents to offspring through their genes.
heredity
Describes the genotype of a trait for which the two alleles an individual carries differ from each other.
heterozygous
Describes the genotype of a trait for which the two alleles an individual carries are the same.
homozygous
The case in which the heterozygote has a phenotype intermediate between those of the two homozygotes; an example is pink snapdragons, with an appearance intermediate between that of a homozygote for white flowers and a homozygote for red flowers.
incomplete dominance
Genes that are close to each other on a chromosome and so are more likely than others to be inherited together.
linked gene
The principle that allele pairs for different genes separate independently in meiosis, so the inheritance of one trait generally does not influence the inheritance of another trait (the exception, unknown to Mendel, occurs with linked genes).
Mendel’s law of independent assortment
The principle that during the formation of gametes, the two alleles for a gene separate, so that half the gametes carry one allele, and half the gametes carry the other.
Mendel’s law of segregation
The case in which a single gene has more than two possible alleles.
multiple allelism
In genetics, a type of family tree that maps the occurrence of a trait in a family, often over many generations.
pedigree
The manifested structure, function, and behaviors of an individual; the expression of the genotype of an organism.
phenotype
A phenomenon in which an individual gene influences multiple traits.
pleiotropy
Describes a trait that is influenced by many different genes.
polygenic
A diagram showing the possible outcomes of a cross between two individuals; the possible crosses are shown in the manner of a multiplication table.
Punnett square
Describes an allele with a phenotypic effect that is masked by a dominant allele for that trait
recessive
A trait controlled by a gene on a sex chromosome
sex-linked trait
A trait that is determined by instructions on only one gene; examples are a cleft chin, a widow’s peak, and unattached earlobes.
single-gene trait
A mating in which a homozygous recessive individual is bred with individuals of unknown genotype that have the dominant phenotype. This type of cross can reveal the unknown genotype by the observed characteristics, or phenotypes, of the offspring.
test-cross
Describes a population of organisms in which, for a given trait, the offspring of crosses of individuals within the population always show the same trait; for example, the offspring of pea plants that are true-breeding for round peas always have round peas.
true-breeding
