Ch 12: Mendel's Experiments and Heredity

Question 1

allele

Answer 1

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

Question 2

autosomes

Answer 2

any of the non-sex chromosomes

Question 3

blending theory of inheritance

Answer 3

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

Question 4

codominance

Answer 4

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

Question 5

continuous variation

Answer 5

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

Question 6

dihybrid

Answer 6

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

Question 7

discontinuous variation

Answer 7

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

Question 8

dominant

Answer 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

Question 9

dominant lethal

Answer 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

Question 10

epistasis

Answer 10

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

Question 11

Answer 11

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

Question 12

Answer 12

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

Question 13

genotype

Answer 13

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

Question 14

heterozygous

Answer 14

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

Question 15

hemizygous

Answer 15

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

Question 16

homozygous

Answer 16

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

Question 17

law of dominance

Answer 17

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

Question 17

hybridization

Answer 17

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

Question 18

incomplete dominance

Answer 18

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

Question 18

law of independent assortment

Answer 18

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

Question 19

law of segregation

Answer 19

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

Question 20

linkage

Answer 20

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

Question 21

model system

Answer 21

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

Question 22

monohybrid

Answer 22

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

Question 23

Answer 23

parental generation in a cross

Question 24

phenotype

Answer 24

observable traits expressed by an organism

Question 25

product rule

Answer 25

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

Question 26

Punnett square

Answer 26

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

Question 27

recessive

Answer 27

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

Question 28

recessive lethal

Answer 28

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

Question 29

reciprocal cross

Answer 29

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

Question 30

sex-linked

Answer 30

any gene on a sex chromosome

Question 31

sum rule

Answer 31

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

Question 32

test cross

Answer 32

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

Question 33

trait

Answer 33

variation in the physical appearance of a heritable characteristic

Question 34

X-linked

Answer 34

gene present on the X, but not the Y chromosome