Chapter 14: Mendel and the Gene Idea

Question 1

additional rule

Answer 1

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.

Question 2

allele

Answer 2

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

Question 3

amniocentesis

Answer 3

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.

Question 4

carrier

Answer 4

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.

Question 5

character

Answer 5

An observable heritable feature that may vary among individuals.

Question 6

chorionic villus sampling (CVS)

Answer 6

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

Question 7

codominance

Answer 7

The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

Question 8

complete dominance

Answer 8

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

Question 9

cystic fibrosis

Answer 9

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.

Question 10

dihybrid

Answer 10

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.

Question 11

dihybrid cross

Answer 11

A cross between two organisms that are each heterozygous for both of the characters being followed (or the self-pollination of a plant that is heterozygous for both characters).

Question 12

dominant allele

Answer 12

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

Question 13

epistasis

Answer 13

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

Question 14

F1 generation

Answer 14

The first filial, hybrid (heterozygous) offspring arising from a parental (P generation) cross.

Question 15

F2 generation

Answer 15

The offspring resulting from interbreeding (or self-pollination) of the hybrid FF1 generation.

Question 16

genotype

Answer 16

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

Question 17

hybridization

Answer 17

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

Question 18

incomplete dominance

Answer 18

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

Question 19

law of independent assortment

Answer 19

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.

Question 20

law of segregation

Answer 20

Mendel’s first law, stating that the two alleles in a pair segregate (separate from each other) into different gametes during gamete formation.

Question 21

monohybrid

Answer 21

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.

Question 22

monohybrid cross

Answer 22

A cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant).

Question 23

multiplication rule

Answer 23

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

Question 24

norm of reaction

Answer 24

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

Question 25

P generation

Answer 25

The true-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance; P stands for “parental.”

Question 26

pedigree

Answer 26

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

Question 27

phenotype

Answer 27

The observable physical and physiological traits of an organism, which are determined by its genetic makeup

Question 28

pleiotropy

Answer 28

The ability of a single gene to have multiple effects

Question 29

polygenic inheritance

Answer 29

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

Question 30

Punnett square

Answer 30

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

Question 31

quantitative character

Answer 31

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

Question 32

recessive allele

Answer 32

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

Question 33

sickle-cell disease

Answer 33

A recessively inherited human blood disorder in which a single nucleotide change in the β-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals.

Question 34

Tay-Sachs disease

Answer 34

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.

Question 35

testcross

Answer 35

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.

Question 36

trait

Answer 36

One of two or more detectable variants in a genetic character.

Question 37

true-breeding

Answer 37

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