Chapter 5

Question 1

complete dominance

Answer 1

when the dominant allele completely covers up the recessive allele

Question 2

incomplete dominance

Answer 2

refers to a genetic situation in which one allele does not completely dominate another allele, and therefore results in a new phenotype

(ex. A child with wavy hair as a result of one parent’s curly hair and the other’s straight hair)
- BLENDING

Question 3

co-dominance

Answer 3

Relating to two alleles of a gene pair in a heterozygote that are both fully expressed (no blending, both expressed)
ex. black and white spots

Question 4

incomplete penetrance

Answer 4

Refers to a genotype that does not always express the expected phenotype. Some individuals possess the genotype for a trait but do not express the phenotype.

Question 5

penetrance

Answer 5

Percentage of individuals with a particular genotype that express the phenotype expected of that genotype.

Question 6

expressivity

Answer 6

Degree to which a trait is expressed.

Question 7

lethal allele

Answer 7

Causes the death of an individual organism, often early in development, and so the organism does not appear in the progeny of a genetic cross. Recessive lethal alleles kill individual organisms that are homozygous for the allele; dominant lethals kill both heterozygotes and homozygotes

Question 8

multiple alleles

Answer 8

Presence in a group of individuals of more than two alleles at a locus. However, each member of the group has only two of the possible alleles.

Question 9

compound heterozygote

Answer 9

An individual with two different recessive alleles at a locus that results in a recessive phenotype.

Question 10

gene interaction

Answer 10

Interaction between genes at different loci that affect the same characteristic.

Question 11

epistasis

Answer 11

Type of gene interaction in which a gene at one locus masks or suppresses the effects of a gene at a different locus.

Question 12

epistatic gene

Answer 12

Masks or suppresses the effect of a gene at a different locus.

Question 13

hypostatic gene

Answer 13

Gene that is masked or suppressed by the action of a gene at a different locus.

Question 14

complementation test

Answer 14

Test designed to determine whether two different mutations are at the same locus (are allelic) or at different loci (are nonallelic). Two individuals that are homozygous for two independently derived mutations are crossed, producing F1 progeny that are heterozygous for the mutations. If the mutations are at the same locus, the F1 will have a mutant phenotype. If the mutations are at different loci, the F1 will have a wild-type phenotype.

Question 15

complementation

Answer 15

Two different mutations in the heterozygous condition are exhibited as the wild-type phenotype; indicates that the mutations are at different loci.

Question 16

sex-influenced characteristic

Answer 16

Characteristic encoded by autosomal genes that are more readily expressed in one sex. For example, an autosomal dominant gene may have higher penetrance in males than in females or an autosomal gene may be dominant in males but recessive in females.

Question 17

sex-limited characteristic

Answer 17

Characteristic encoded by autosomal genes and expressed in only one sex. Both males and females carry genes for sex-limited characteristics, but the characteristics appear in only one of the sexes.

Question 18

cytoplasmic inherticance

Answer 18

Inheritance of characteristics encoded by genes located in the cytoplasm. Because the cytoplasm is usually contributed entirely by only one parent, most cytoplasmically inherited characteristics are inherited from a single parent.

Question 19

genetic maternal effect

Answer 19

Determines the phenotype of an offspring. With genetic maternal effect, an offspring inherits genes for the characteristics from both parents, but the offspring’s phenotype is determined not by its own genotype but by the nuclear genotype of its mother.

Question 20

genomic imprinting

Answer 20

Differential expression of a gene that depends on the sex of the parent that transmitted the gene. If the gene is inherited from the father, its expression differs from that if the gene is inherited from the mother.

Question 21

epigenetics

Answer 21

Phenonmena due to alterations to DNA that do not include changes in the base sequence; often affect the way in which the DNA sequences are expressed. Such alterations are often stable and heritable in the sense that they are passed from one cell to another.

Question 22

anticipation

Answer 22

Increasing severity or earlier age of onset of a genetic trait in succeeding generations. For example, symptoms of a genetic disease may become more severe as the trait is passed from generation to generation.

Question 23

temperature sensitive allele

Answer 23

Expressed only at certain temperatures.

Question 24

phenocopy

Answer 24

Phenotype that is produced by environmental effects and is the same as the phenotype produced by a genotype.

Question 25

discontinuous characteristic

Answer 25

Exhibits only a few, easily distinguished phenotypes. An example is seed shape in which seeds are either round or wrinkled.

Question 26

continuous characteristic

Answer 26

Displays a large number of possible phenotypes that are not easily distinguished, such as human height.

Question 27

quantitative characteristic

Answer 27

Continuous characteristic; displays a large number of possible phenotypes, which must be described by a quantitative measurement.

Question 28

polygenic characteristic

Answer 28

Encoded by genes at many loci.

Question 29

pleiotropy

Answer 29

A single genotype influences multiple phenotypes.

Question 30

multifactoral characteristic

Answer 30

Determined by multiple genes and environmental factors.