Chapter 4 - BB (1)

Flowered plants f2 purple and white flowered purplein

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Unformatted text preview: ea white X true-breeding white white – F1: Purple flowered plants – F2: Purple- and white-flowered Purplein a 3:1 ratio in These results were not surprising F2 generation ratio - 9 purple : 7 white flower color is determined by two flower different genes different – C (one purple-color-producing) allele is dominant to c (white) (white) – P (another purple-color-producing) allele is dominant to p (white) (white) – cc or pp masks P or C alleles, cc or masks producing white color producing Epistasis - situation in which a gene can mask the phenotypic effects of another gene phenotypic Epistatic interactions - two (or more) different Epistatic proteins participate in a common cellular function proteins – an enzymatic pathway Colorless precursor Enzyme C Colorless intermediate Enzyme P Purple pigment If an individual is homozygous for either recessive allele – – – It will not make any functional enzyme C or enzyme P Therefore, the flowers remain white Complementation Two-Gene Interaction - 8:4:3:1 ratio Cream-Eye allele in Drosophila Cream-Eye Drosophila – Calvin Bridges Calvin – rare fly with cream-colored eyes, in a true-breeding rare culture of flies with eosin eyes culture 1. A new mutation changed the eosin allele into a cream 1. allele allele 2. A mutation occurred in another gene that modified the 2. expression of the eosin allele expression The Hypothesis The Cream-colored eyes in fruit flies are due to the Cream-colored effect of a second gene that modifies the expression of Cross Outcome P cross: the eosin allele the Cream­eyed male X F1: all red eyes wild­type female F1 cross: F1 brother X F1 F2: 104 females with red sister eyes 47 males with red eyes 44 males with eosin eyes 14 males with cream eyes One possibility is that the cream allele is an autosomal One recessive allele recessive – C = Normal allele Does not modify t...
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