Chapter 12

Question 1

gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes

Answer 1

Allele

Question 2

any of the non-sex chromosomes

Answer 2

Autosomes

Question 3

hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance

Answer 3

Blending theory of inheritance

Question 4

in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic

Answer 4

Codominance

Question 5

inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them

Answer 5

Continuous variation

Question 6

result of a cross between two true-breeding parents that express different traits for two characteristics

Answer 6

Dihybrid

Question 7

inheritance pattern in which traits are distinct and are transmitted independently of one another

Answer 7

Discontinuous variation

Question 8

trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait

Answer 8

Dominant

Question 9

inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age

Answer 9

Dominant Lethal

Question 10

antagonistic interaction between genes such that one gene masks or interferes with the expression of another

Answer 10

Epistasis

Question 11

F1

Answer 11

first filial generation in a cross; the offspring of the parental generation

Question 12

second filial generation produced when F1 individuals are self-crossed or fertilized with each other

Answer 12

F2

Question 13

underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism

Answer 13

Genotype

Question 14

presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant

Answer 14

Hemizygous

Question 15

having two different alleles for a given gene on the homologous chromosome

Answer 15

Heterozygous

Question 16

having two identical alleles for a given gene on the homologous chromosome

Answer 16

Homozygous

Question 17

process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring

Answer 17

Hybridization

Question 18

in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype

Answer 18

Incomplete dominance

Question 19

in a heterozygote, one trait will conceal the presence of another trait for the same characteristic

Answer 19

Law of dominance

Question 20

genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur

Answer 20

Law of independent assortment

Question 21

paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors

Answer 21

law of segregation

Question 22

phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together

Answer 22

linkage

Question 23

species or biological system used to study a specific biological phenomenon to be applied to other different species

Answer 23

model system

Question 24

result of a cross between two true-breeding parents that express different traits for only one characteristic

Answer 24

Monohybrid

Question 25

parental generation in a cross

Answer 25

P0

Question 26

observable traits expressed by an organism

Answer 26

Phenotype

Question 27

probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone

Answer 27

Product rule

Question 28

visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid

Answer 28

Punnett square

Question 29

trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed

Answer 29

Recessive

Question 30

inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, nonlethal phenotype

Answer 30

Recessive lethal

Question 31

paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross

Answer 31

Reciprocal cross

Question 32

any gene on a sex chromosome

Answer 32

sex-linked

Question 33

probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities

Answer 33

Sum rule

Question 34

cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait

Answer 34

Test cross

Question 35

variation in the physical appearance of a heritable characteristic

Answer 35

Trait

Question 36

gene present on the X, but not the Y chromosome

Answer 36

X-linked