Chapter 5

Question 1

Complete dominance

Answer 1

same phenotype is expressed in homozygotes (AA) and in heterozygotes (Aa); only the dominant allele is expressed in a heterozygote

Question 2

Incomplete dominance

Answer 2

phenotype falls between two homozygote and dominance is incomplete

Question 3

codominance

Answer 3

phenotype of heterozygote includes the phenotypes of both homozygotes

Question 4

incomplete penetrance

Answer 4

the genotype does not always produce the expected phenotype

Question 5

Penetrance

Answer 5

the percentage of individual organisms having a particular genotype that express the expected phenotype

Question 6

Expressivity

Answer 6

the degree to which a trait is expressed

Question 7

lethal allele

Answer 7

causes death at an early stage of development , before birth, so that some genotypes do not appear among the progeny.

• one or more genotypes are missing from the progeny of a cross

Question 8

Multiple alleles

Answer 8

when two alleles are present in loci

Question 9

Gene interaction

Answer 9

genes at different loci contribute to the determination of a single phenotypic characteristic

Question 10

epistasis

Answer 10

effect of gene interaction is that one gene masks (hides) the effect of another gene at a different locus

Question 11

How is epistasis different from dominance?

Answer 11

dominance does it on the same locus, in epistasis, the gene that does the masking is an epistatic gene

Question 12

hypostatic gene

Answer 12

gene whose effect is masked

Question 13

recessive epistasis

Answer 13

presence of two recessive alleles (homozygous genotype) inhibits the expression of an allele at a different locus

Question 14

dominant epistasis

Answer 14

only a single copy of an allele is required to inhibit the expression of an allele at a different locus

Question 15

duplicate recessive epistasis

Answer 15

2 recessive alleles at either two different loci are capable of suppressing a phenotype

Question 16

complementation test

Question 17

when does a lack of complementation occur?

Answer 17

when two recessive mutations occur at the same locus, producing a mutant phenotype

Question 18

complementation

Answer 18

individual organism that has two recessive mutations has a wild-type phenotype, indicating that the mutations are at nonallelic genes

Question 19

sex-influenced characteristics

Answer 19

determine by autosomal genes and are inherited and readily expressed in one sex
- - higher penetrance in one of the sexes

Question 20

sex-linked characteristic

Answer 20

genes located on the sex chromosomes

Question 21

sex-limited characteristic

Answer 21

autosomal genes who expression is limited to one sex
- the trait has zero penetrance in the other sex

Question 22

Genetic maternal effect

Answer 22

nuclear genotype of the maternal parent
- genes inherited from both parents but phenotype is determined by the genotype its mother

Question 23

cytoplasmic inheritance

Answer 23

cytoplasmic genes, which are usually inherited from only one parent

-Typically inherited by maternal parent

Question 24

genomic imprinting

Answer 24

genes whose expression is affected by the sex of the transmitting parent

Question 25

epigenetics

Answer 25

phenomena due to alterations in DNA that due not include changes in the base sequence, often affects the way in which DNA sequences are expressed.
- reversible changes in DNA that do not alter the base sequence but may affect how a gene is expressed

Question 26

anticipation

Answer 26

Genetic trait becomes strongly expressed or is expressed at an earlier age as it is passed from generation to generation
- caused by an unstable region of DNA that increases in size from generation to generation

Question 27

phenocopy

Answer 27

produced by environmental effects that mimics the phenotype produced by a genotype