Chapter 3

Question 1

gene

Answer 1

Genetic factor that helps determine a trait; often defined at the molecular level as a DNA sequence that is transcribed into an RNA molecule.

Question 2

allele

Answer 2

One of two or more alternate forms of a gene.

Question 3

locus

Answer 3

Position on a chromosome where a specific gene is located.

Question 4

genotype

Answer 4

The set of genes possessed by an individual organism.

Question 5

homozygous

Answer 5

Refers to an individual organism that possesses two identical alleles at a locus.

Question 6

heterozygous

Answer 6

Refers to an individual organism that possesses two different alleles at a locus.

Question 7

phenotype

Answer 7

Appearance or manifestation of a characteristic.

Question 8

monohybrid cross

Answer 8

A cross between two individuals that differ in a single characteristic—more specifically, a cross between individuals that are homozygous for different alleles at the same locus (AA × aa); also refers to a cross between two individuals that are heterozygous for two alleles at a single locus (Aa × Aa).

Question 9

P (parental) generation

Answer 9

First set of parents in a genetic cross.

Question 10

F1 (first filial) generation

Answer 10

Offspring of the initial parents (P) in a genetic cross.

Question 11

reciprocal cross

Answer 11

Crosses in which the phenotypes of the male and female parents are reversed. For example, in one cross, a tall male is crossed with a short female and, in the other cross, a short male is crossed with a tall female.

Question 12

F2 (second filial) generation

Answer 12

Offspring of the F1 generation in a genetic cross; the third generation of a genetic cross.

Question 13

dominant

Answer 13

Refers to an allele or a phenotype that is expressed in homozygotes (AA) and in heterozygotes (Aa); only the dominant allele is expressed in a heterozygote phenotype.

Question 14

recessive

Answer 14

Refers to an allele or phenotype that is expressed only when the recessive allele is present in two copies (homozygous). The recessive allele is not expressed in the heterozygote phenotype.

Question 15

principle of segregation (Mendel’s first law)

Answer 15

important principle of heredity discovered by Mendel that states that each diploid individual possesses two alleles at a locus and that these two alleles separate when gametes are formed, one allele going into each gamete.

Question 16

concept of dominance

Answer 16

Principle of heredity discovered by Mendel stating that, when two different alleles are present in a genotype, only one allele may be expressed in the phenotype. The dominant allele is the allele that is expressed, and the recessive allele is the allele that is not expressed.

Question 17

chromosome theory of heredity

Answer 17

States that genes are located on chromosomes.

Question 18

backcross

Answer 18

Cross between an F1 individual and one of the parental (P) genotypes.

Question 19

probability

Answer 19

Likelihood of the occurrence of a particular event; more formally, the number of times that a particular event occurs divided by the number of all possible outcomes. Probability values range from 0 to 1.

Question 20

multiplication rule

Answer 20

States that the probability of two or more independent events occurring together is calculated by multiplying the probabilities of each of the individual events.

Question 21

addition rule

Answer 21

States that the probability of any of two or more mutually exclusive events occurring is calculated by adding the probabilities of the individual events.

Question 22

conditional probability

Answer 22

Probability that is modified by additional information that another event has occurred.

Question 23

testcross

Answer 23

A cross between an individual with an unknown genotype and an individual with the homozygous recessive genotype.

Question 24

wild type

Answer 24

The trait or allele that is most commonly found in natural (wild) populations.

Question 25

dihybrid cross

Answer 25

A cross between two individuals that differ in two characteristics—more specifically, a cross between individuals that are homozygous for different alleles at the two loci (AA BB × aa bb); also refers to a cross between two individuals that are both heterozygous at two loci (Aa Bb × Aa Bb).

Question 26

principle of independent assortment (Mendel’s second law)

Answer 26

Important principle of heredity discovered by Mendel that states that genes encoding different characteristics (genes at different loci) separate independently; applies only to genes located on different chromosomes or to genes far apart on the same chromosome.

Question 27

chi-square goodness of fit test

Answer 27

Statistical test used to evaluate how well a set of observed values fit the expected values. The probability associated with a calculated chi-square value is the probability that the differences between the observed and the expected values may be due to chance.