An observable heritable feature that may vary among individuals.
One of two or more detectable variants in a genetic character.
Referring to organisms that produce offspring of the same variety over many generations of self-pollination.
In genetics, the mating, or crossing, of two true-breeding varieties.
The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental.”
The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.
The offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generation.
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.
An allele that is fully expressed in the phenotype of a heterozygote.
An allele whose phenotypic effect is not observed in a heterozygote.
law of segregation
Mendel’s first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.
A diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype.
Having two identical alleles for a given gene.
Having two different alleles for a given gene.
The observable physical and physiological traits of an organism, which are determined by its genetic makeup.
The genetic makeup, or set of alleles, of an organism.
Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring reveals the unknown genotype.
An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles are _________s. For example, parents of genotypes AA and aa produce a __________ of genotype Aa.
A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).
An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb.
A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination
Mendel’s second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes or when they are far enough apart on the same chromosome to behave as though they are on different chromosomes.
A rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities.
A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.
The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele.
The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.
A human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth, followed by death within a few years.
(Greek pleion, more) The ability of a single gene to have multiple effects.
A heritable feature that varies continuously over a range rather than in an either-or fashion.
An additive effect of two or more genes on a single phenotypic character.
norm of reaction
The range of phenotypes produced by a single genotype, due to environmental influences.
Referring to a phenotypic character that is influenced by multiple genes and environmental factors.
A diagram of a family tree with conven- tional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations.
In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is generally phenotypically normal for the disorder but can pass on the recessive allele to offspring.
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; fatal if untreated.
A recessively inherited human blood disorder in which a single nucleotide change in the B-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.
A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after the onset of symptoms.
A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.
chorionic villus sampling (CVS)
A technique associated with prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus.
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