Chapter 9 Definitions

Question 1

Effects from alleles of multiple genes that all contribute to the ultimate phenotype for a given characteristic.

Answer 1

additive effects

Question 2

Alternative versions of a gene.

Answer 2

allele

Question 3

In genetics, an individual who carries one allele for a recessive trait and does not exhibit the trait; if two carriers mate, they may produce offspring that do exhibit the trait.

Answer 3

carrier

Question 4

The case in which a heterozygote displays characteristics of both alleles.

Answer 4

codominance

Question 5

The breeding of organisms that differ in one or more traits.

Answer 5

cross

Question 6

An individual that is heterozygous at two genetic loci.

Answer 6

dihybrid

Question 7

A cross between two individuals that are heterozygous for the same two genetic loci.

Answer 7

dihybrid cross

Question 8

In genetics, describes an allele that masks the phenotypic effect of the other, recessive allele for a trait. The phenotype shows the effect of the dominant allele in both homozygous and heterozygous genotypes.

Answer 8

dominant

Question 9

The genes that an organism carries for a particular trait; also, collectively, an organism’s genetic composition.

Answer 9

genotype

Question 10

The greater resemblance of offspring to their parents than to other individuals in the population, a consequence of the passing of characteristics from parents to offspring through their genes.

Answer 10

heredity

Question 11

Describes the genotype of a trait for which the two alleles an individual carries differ from each other.

Answer 11

heterozygous

Question 12

Describes the genotype of a trait for which the two alleles an individual carries are the same.

Answer 12

homozygous

Question 13

The case in which the heterozygote has a phenotype intermediate between those of the two homozygotes; an example is pink snapdragons, with an appearance intermediate between that of a homozygote for white flowers and a homozygote for red flowers.

Answer 13

incomplete dominance

Question 14

Genes that are close to each other on a chromosome and so are more likely than others to be inherited together.

Answer 14

linked gene

Question 15

The principle that allele pairs for different genes separate independently in meiosis, so the inheritance of one trait generally does not influence the inheritance of another trait (the exception, unknown to Mendel, occurs with linked genes).

Answer 15

Mendel’s law of independent assortment

Question 16

The principle that during the formation of gametes, the two alleles for a gene separate, so that half the gametes carry one allele, and half the gametes carry the other.

Answer 16

Mendel’s law of segregation

Question 17

The case in which a single gene has more than two possible alleles.

Answer 17

multiple allelism

Question 18

In genetics, a type of family tree that maps the occurrence of a trait in a family, often over many generations.

Answer 18

pedigree

Question 19

The manifested structure, function, and behaviors of an individual; the expression of the genotype of an organism.

Answer 19

phenotype

Question 20

A phenomenon in which an individual gene influences multiple traits.

Answer 20

pleiotropy

Question 21

Describes a trait that is influenced by many different genes.

Answer 21

polygenic

Question 22

A diagram showing the possible outcomes of a cross between two individuals; the possible crosses are shown in the manner of a multiplication table.

Answer 22

Punnett square

Question 23

Describes an allele with a phenotypic effect that is masked by a dominant allele for that trait

Answer 23

recessive

Question 24

A trait controlled by a gene on a sex chromosome

Answer 24

sex-linked trait

Question 25

A trait that is determined by instructions on only one gene; examples are a cleft chin, a widow’s peak, and unattached earlobes.

Answer 25

single-gene trait

Question 26

A mating in which a homozygous recessive individual is bred with individuals of unknown genotype that have the dominant phenotype. This type of cross can reveal the unknown genotype by the observed characteristics, or phenotypes, of the offspring.

Answer 26

test-cross

Question 27

Describes a population of organisms in which, for a given trait, the offspring of crosses of individuals within the population always show the same trait; for example, the offspring of pea plants that are true-breeding for round peas always have round peas.

Answer 27

true-breeding