Clouded sulfur butterflies are common in our area and can be either yellow or white. While most individuals in the total population are yellow, it is known that a single autosomal gene controls color and that the white allele is completely dominant over the yellow allele. However, when analyzing crosses we find the following results: Yellow male x yellow female = 100% yellow males:100% yellow females Yellow male x yellow female = 100% yellow males:50% white females:50% yellow females Yellow male x white female = 100% yellow males:100% white females Yellow male x yellow female = 100% yellow males:100% white females Yellow male x white female = 100% yellow males:75% white females:25% yellow females What do these results suggest about the genetic inheritance patterns of this trait in clouded sulfur butterflies? Solution Colias philodice, the common yellow butterfly, also sometimes called the clouded sulphur butterfly. The different forms of a gene that are found at a locus along a given chromosome are known as alleles. Diploid organisms have two alleles for each autosomal gene; one inherited from the mother, one inherited from the father. If the phenotype associated with a gene is observed, in an individual having only one copy, the allele is said to be autosomal dominant. The phenotype will be observed whether the individual has one copy of the allele (heterozygous) or has two copies of the allele (homozygous). Females carrying a dominant allele w+ at a single autosomal locus are white instead of the species-specific red, orange, or yellow displayed by their homozygous recessive ww sisters and by all males. The cross is outlined below: We know that females are XX homogametic males are XY heterogametic. P generation: Female w+w+ (white) × Male w (yellow) F1 generation: Female w+w (white) × Male w+ (white) The fact that all the F1 progeny had white color wings, suggests that the wild-type (w+) allele is dominant over the yellow allele..

1. Clouded sulfur butterflies are common in our area and can be either yellow or white. While most
individuals in the total population are yellow, it is known that a single autosomal gene controls
color and that the white allele is completely dominant over the yellow allele. However, when
analyzing crosses we find the following results:
Yellow male x yellow female = 100% yellow males:100% yellow females
Yellow male x yellow female = 100% yellow males:50% white females:50% yellow females
Yellow male x white female = 100% yellow males:100% white females
Yellow male x yellow female = 100% yellow males:100% white females
Yellow male x white female = 100% yellow males:75% white females:25% yellow females
What do these results suggest about the genetic inheritance patterns of this trait in clouded sulfur
butterflies?
Solution
Colias philodice, the common yellow butterfly, also sometimes called the clouded sulphur
butterfly.
The different forms of a gene that are found at a locus along a given chromosome are known as
alleles. Diploid organisms have two alleles for each autosomal gene; one inherited from the
mother, one inherited from the father.
If the phenotype associated with a gene is observed, in an individual having only one copy, the
allele is said to be autosomal dominant. The phenotype will be observed whether the individual
has one copy of the allele (heterozygous) or has two copies of the allele (homozygous).
Females carrying a dominant allele w+ at a single autosomal locus are white instead of the
species-specific red, orange, or yellow displayed by their homozygous recessive ww sisters and
by all males.
The cross is outlined below: We know that females are XX homogametic males are XY
heterogametic.
P generation:
Female w+w+ (white) × Male w (yellow)
F1 generation:
Female w+w (white) × Male w+ (white)
The fact that all the F1 progeny had white color wings, suggests that the wild-type (w+) allele is
dominant over the yellow allele.