Lecture 3

Question 1

incomplete dominance

Answer 1

phenotype of the heterozygous hybrid is the intermediate between the homozygous parents
genotype and phenotype 1:2:1
phenotype caused by half the amount of gene product formed

Question 2

codominance

Answer 2

phenotypes of both alleles are observed equally
genotype and phenotype: 1:2:1
ex. blood type (with multiple alleles)

Question 3

complete dominance

Answer 3

one allele is expressed and the other is not

genotype: 1:2:1
phenotype: 3:1

Question 4

multiple alleles

Answer 4

more than two alleles in a single gene, often have a hierarchy of dominance for alleles
ex. coat color in guinea pigs

Question 5

multiple gene control

Answer 5

multiple genes can control the same process, will have 9:3:3:1
if two mutants complement, they have mutations in different genes

Question 6

epistasis

Answer 6

one gene interferes with or masks another gene

Question 7

lethal alleles

Answer 7

mutations in genes that are essential for viability

Question 8

penetrance

Answer 8

% with expected phenotype for a give genotype

ex. 100% penetrance: Mendel’s Peas and ABO
ex. incomplete penetrance: retinoblastoma, huntington’s disease

Question 9

expressivity

Answer 9

variation in intensity of phenotype for a given genotype

ex. PKU results in severe mental retardation if untreated

Question 10

polygenic traits

Answer 10

phenotype controlled by many genes with many alleles
produce a continuum of phenotypes
ex. Height