6 - twogene inheritance patterns Flashcards
What is a two-factor gene?
crosses consider the inheritance of alleles of two separate loci, two genes control the expression of two separate traits
Give an example with yellow/green seeds and round/wrinkle seeds for two gene inheritance
YR Yr yR yr vs YR Yr yR yr
= 9 yellow, round, 3 yellow, wrinkled, 3 green, round, 1 green wrinkled
How can can we observe two-gene inheritance?
observed by certain phenotypes have disappeared in F1 gen but reappeared in F2 gen, all four possible in F2
With enough offspring, ratio of 9:3:3:1 can be observed
What should we consider with two gene inheritance patterns?
each gamete has 1 allele for seed color/shape
4 diff types of gametes are possible of r each f1 heterozygote (each seed color allele can be found in a gamete with either of the two seed shape alleles)
bc 4 gametes possible for each F1 male and female, there are 16 possible fertilization combos to prod f2 generation
16 possible outcomes result in 9 diff genotypes determining 4 dif phenotypes = 9:3:3:1
What is the law of independant assortment?
alleles of different genes segregate independantly during sexual reproduction
the inheritance of an allele for one gene is unaffected by the inheritance of an allele at another gene locus
What is epistasis?
when alleles of one gene mask the expression of alleles of another gene? Messes up the 9:3:3:1 ratio
New ratio is 9:4:3 phenotype ratio in F2 gen
When recessive alleles present at one locus mask a different gene locus. - recessive epistasis
the ‘4’ encompasses the 3:1 classes of 9:3:3:1 segregation ratio
Give an example of epistasis in labrador retrievers
Labrador Retrievers
O Dominant allele B
– black pigment → black
O Recessive allele b
- brown pigment → chocolate
O Dominant allele E
– needed to deposit pigment in
hair shaft
O Recessive allele e
– pigment cannot be
deposited → yellow
What is albinism an example of?
Recessive epistasis due to the white coat color resulting of a recessive epistatic allele
What is dominant epistasis?
When a dominant allele present at one locus masks expression of alleles of another gene
12:2:1 phenotype in F2 gen
Give an example of dominant epistasis in gray horses
O Grey horses
O G_ _ _ - grey horse at maturity
O gg_ _ - horse that is not grey at
maturity
O ggE_ - black horse
O ggee – chestnut horse
O F2 results (cross GgEe by GgEe):
O 12 grey: 3 black: 1 chestnut
Give a quick summary of two-gene inheritance patterns
two-factor x’s investigate the patterns of inheritance involves when two genes (traits) are involved
segregation and subsequent inheritance of alleles for each gene occur independently
a 9:3:3:1 phenotypic ratio in F2 gen
Epistasis dominance changes ratio to: 12:3:1
Epistasis recessive changes ratio to 9:3:4
