Modification of Mendelian Ratios

Question 1

intra-allelic gene interactions

Answer 1

interaction between alleles of a locus

types: complete dominance, incomplete dominance, codominance, overdominance

Question 2

incomplete dominance

Answer 2

heterozygous genotype exhibits an intermediate phenotype between the phenotypes of the 2 homozygous genotypes
neither allele is dominant
single gene, 2 alleles
(same ratio as codominance)

Question 3

codominance

Answer 3

both alleles are expressed in a heterozygote
F2= 1:2:1
can exhibit either one or both alleles
heterozygotes are codominant
- distinct expression of both gene products (alleles)
(same ratio as incomplete dominance)

ex: MN blood groups

Question 4

complete dominance

Answer 4

one allele dominates

Question 5

simple dominance hierarchy

multiple allelic series-relationship

Answer 5

each allele is dominant to the remaining alleles in a series
alleles can be arranged in order of dominance
# of phenotypes= # of alleles
ex: coat color in rabbits

Question 6

Multiple allelic series relationship

Answer 6

incomplete dominance or codominance
# of possible phenotypes= # of possible genoypes
ex: A,B,O blood groups

Question 7

Inter-allelic interactions

Answer 7

gene interactions between non-allelic genes

type: epistasis
- duplicate recessive
- duplicate dominant
- recessive
- dominant

Question 8

epistasis

Answer 8

expression of one gene or gene a pair masks or modifies the expression of another gene/gene pair; modified F2 ratio (9:3:3:1 ratio)
occurs in sixteenths (clue that 2 genes are involved in controlling the observed phenotype)
principles of segregation & independent assortment hold true (not dominance/recessiveness)
*more than one phenotype –> clue that it’s epistasis

Question 9

Recessive Epistasis

Answer 9

9:3:4

ex: color pigment & pigment distribution
one gene produces pigment
on gene reduces pigment
A/a and B/b
when b is homozygous, color effects Gene A are masked

Question 10

Dominant Epistasis

Answer 10

12:3:1

dominant allele at one gene locus masks the expression of alleles at a second locus

Question 11

Duplicate Recessive Epistasis

Answer 11

9:7

ex: flower color
A/a and B/b
presence of a dominant allele of each gene is required for the production of purple flower color
all other allele combos= white flower color
(homozygous condition of either recessive allele masks the expression of the dominant allele at the other locus)

Question 12

Duplicate Dominant Epistasis

Answer 12

15:1
2 genes provide an alternative genetic determination of a specific genotype
the presence of a dominant allele of either gene= dominant phenotype