Exceptions/Extensions to Mendel's Rules

Question 1

variable expressivity

Answer 1

same gene, but phenotypes different severity in forms of expression

Question 2

reduced penetrance

Answer 2

all or nothing expression phenotype, allele is present but phenotype if absent

Question 3

incomplete dominance

Answer 3

heterozygous phenotype is a blend of both homozygous phenotypes
ex. RR (red) x rr (white) = Rr (pink)

Question 4

codominance

Answer 4

both alleles are equally expressed
ex. blood type AB

Question 5

pleiotropy

Answer 5

one gene, multiple phenotypic effects (plenty of effects)

Question 6

genetic heterogeneity

Answer 6

one phenotype, multiple genetic causes

Question 7

multiple alleles

Answer 7

more than two gene versions in the population (but each individual still has only two)