Ch. 3 Basic Principles of Heredity

Question 1

gene

Answer 1

inherited 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 alternative forms of a gene

Question 3

locus

Answer 3

specific place on a chromosome occupied by an allele

Question 4

genotype

Answer 4

set of alleles possessed by an individual organism

Question 5

homozygous

Answer 5

an individual organism possessing two of the same alleles at a locus

Question 6

heterozygous

Answer 6

an individual organism possessing two different alleles at a locus

Question 7

phenotype

Answer 7

the appearance or manifestation of a characteristic

Question 8

monohybrid cross

Answer 8

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 x aa); also refers to a cross between two individuals that are heterozygous for two alleles at a single locus (Aa x 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

pair of 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 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 in homozygotes (aa); the recessive allele is not expressed in the heterozygote (Aa) phenotype

Question 15

principle of segregation (Medel’s first law)

Answer 15

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

theory stating 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

Punnett square

Answer 19

shorthand method of determining the outcome of a genetic cross; on a grid, the gametes of one parent are written along the upper edge and the gametes of the other parent are written along the left-hand edge; within the cells of the grid, the alleles in the gametes are combined to form the genotypes of the offspring

Question 20

probability

Answer 20

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 21

multiplication rule

Answer 21

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

Question 22

addition rule

Answer 22

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

Question 23

conditional probability

Answer 23

probability that is modified by additional information that another event has occurred

Question 24

testcross

Answer 24

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

Question 25

wild type

Answer 25

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

Question 26

dihybrid cross

Answer 26

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

Question 27

principle of independent assortment (Mendel’s second law)

Answer 27

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 28

chi-square goodness-of-fit test

Answer 28

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 are due to chance