AP Biology Vocabulary & Roots: Ch. 14
1. allele-Any of the alternative versions of a gene that produce distinguishable phenotypic effects.
2. 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.
3. carrier-In genetics, an individual who is heterozygous at a given genetic locus, with one normal
allele and one recessive allele. The heterozygote is phenotypically dominant for the character
determined by the gene but can pass on the recessive allele to offspring.
4. character-An observable heritable feature.
5. 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.
6. codominance-The situation in which the phenotypes of both alleles are exhibited in the
heterozygote because both alleles affect the phenotype in separate, distinguishable ways.
7. complete dominance-The situation in which the phenotypes of the heterozygote and dominant
homozygote are indistinguishable.
8. 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.
9. 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.
10. dominant allele-An allele that is fully expressed in the phenotype of a heterozygote.
11. epistasis- A type of gene interaction in which one gene alters the phenotypic effects of another
gene that is independently inherited.
12. F1 generation-The first filial, or hybrid, offspring in a series of genetic crosses.
13. F2 generation-Offspring resulting from interbreeding of the hybrid F1 generation.
14. genotype-The genetic makeup, or set of alleles, of an organism.
15. heterozygous- Having two different alleles for a given gene.
16. homozygous- Having two identical alleles for a given gene.
17. 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.
18. hybridization-In genetics, the mating, or crossing, of two true-breeding varieties.
19. incomplete dominance-The situation in which the phenotype of heterozygotes is intermediate
between the phenotypes of individuals homozygous for either allele.
20. law of independent assortment-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.
21. law of segregation-Mendel’s first law, stating that the two alleles in a pair segregate (separate)
into different gametes during gamete formation.
22. 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.
23. multifactorial-Referring to a phenotypic character that is influenced by multiple genes and
environmental factors.
24. norm of reaction-The range of phenotypes produced by a single genotype, due to
environmental influences.
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25. P generation-The parent individuals from which offspring are derived in studies of inheritance;
P stands for “parental.”
26. pedigree-A diagram of a family tree showing the occurrence of heritable characters in parents
and offspring over multiple generations.
27. phenotype-The physical and physiological traits of an organism, which are determined by its
genetic makeup.
28. pleiotropy-The ability of a single gene to have multiple effects.
29. polygenic inheritance-An additive effect of two or more genes on a single phenotypic
character.
30. Punnett square-A diagram used in the study of inheritance to show the predicted results of
random fertilization in genetic crosses.
31. quantitative character-A heritable feature that varies continuously over a range rather than in
an either-or fashion.
32. recessive allele-An allele whose phenotypic effect is not observed in a heterozygote.
33. sickle-cell disease-A human genetic disease caused by a recessive allele that results in the
substitution of a single amino acid in a globin polypeptide that is part of the hemoglobin protein;
characterized by deformed red blood cells (due to protein aggregation) that can
34. 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, followed by
death within a few years.
35. testcross-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.
36. trait- Any detectable variant in a genetic character.
37. true-breeding-Referring to plants that produce offspring of the same variety when they selfpollinate.
Word Roots
-centesis = a puncture (amniocentesis: a technique for determining genetic abnormalities in a fetus
by the presence of certain chemicals or defective fetal cells in the amniotic fluid, obtained by
aspiration from a needle inserted into the uterus)
co- = together (codominance: phenotype in which both dominant alleles are expressed in the
heterozygote)
di- = two (dihybrid cross: a breeding experiment in which offspring of a cross of parental varieties
differing in two traits are mated)
epi- = beside; -stasis = standing (epistasis: a phenomenon in which one gene alters the expression of
another gene that is independently inherited)
geno- = offspring (genotype: the genetic makeup of an organism)
hetero- = different (heterozygous: having two different alleles for a trait)
homo- = alike (homozygous: having two identical alleles for a trait)
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mono- = one (monohybrid cross: a breeding experiment that crosses offspring of a cross of parental
varieties differing in a single character)
pedi- = a child (pedigree: a family tree describing the occurrence of heritable characters in parents
and offspring across as many generations as possible)
pheno- = appear (phenotype: the physical and physiological traits of an organism)
pleio- = more (pleiotropy: when a single gene impacts more than one characteristic)
poly- = many; gene- = produce (polygenic: an additive effect of two or more gene loci on a single
phenotypic character)
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