AP BIO CH 14

alleles

Alternative versions of a gene that produce distinguishable phenotypic effects.

amniocentesis

A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.

carrier

In genetics, an individual who is heterozygous at a given genetic locus, with one normal allele and one potentially harmful recessive allele. The heterozygote is phenotypically normal for the character determined by the gene but can pass on the harmful allele to offspring.

character

An observable heritable feature.

chorionic villus sampling (CVS)

A technique of prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed and analyzed to detect certain genetic and congenital defects in the fetus.

codominance

The situation in which the phenotypes of both alleles are exhibited in the heterozygote.

complete dominance

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

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; fatal if untreated.

dihybrid

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.

dominant allele

An allele that is fully expressed in the phenotype of a heterozygote.

epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

F1 generation

The first filial, or hybrid, offspring in a series of genetic crosses.

F2 generation

Offspring resulting from interbreeding of the hybrid F1 generation.

genotype

The genetic makeup, or set of alleles, of an organism.

heterozygous

Having two different alleles for a given gene.

homozygous

Having two identical alleles for a given gene.

Huntington's disease

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.

hybridization

In genetics, the mating, or crossing, of two true-breeding varieties.

incomplete dominance

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

law of independent assortment

Mendel's second law, stating that each pair of alleles segregates independently during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes.

law of segregation

Mendel's first law, stating that each allele in a pair separates into a different gamete during gamete formation.

monohybrid

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 monohybrids. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa.

multifactorial

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

norm of reaction

The range of phenotypes produced by a single genotype, due to environmental influences.

P generation

The parent individuals from which offspring are derived in studies of inheritance; P stands for parental.

pedigree

A diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations.

phenotype

The physical and physiological traits of an organism, that are determined by its genetic makeup.

pleiotropy

The ability of a single gene to have multiple effects.

polygenic inheritance

An additive effect of two or more gene loci on a single phenotypic character.

Punnett square

A diagram used in the study of inheritance to show the results of random fertilization in genetic crosses.

quantitative character

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

recessive allele

An allele whose phenotypic effect is not observed in a heterozygote.

sickle-cell disease

A human genetic disease caused by a recessive allele that results in the substitution of a single amino acid in the hemoglobin protein; characterized by deformed red blood cells that can lead to numerous symptoms.

Tay-Sachs disease

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.

testcross

Breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring determines the unknown genotype.

trait

Any detectable variation in a genetic character.

true-breeding

Referring to plants that produce offspring of the same variety when they self-pollinate.