Youve joined a research group studying how populations of le

You’ve joined a research group studying how populations of lemmings, small artic rodents, are affected by recent climate changes. You have been charged with maintaining different laboratory lines of lemmings and recently performed the following crosses between lemmings with coat colors orange, beige, and cream (the animals were not necessarily from pure-breeding lines).

beige x beige -> 3/4 beige, 1/4 cream

beige x cream -> 1/2 beige, 1/2 orange

orange x cream -> 1/2 orange, 1/2 cream

orange x orange -> 3/4 orange, 1/4 cream

Your current mastery of allele and gene interactions led you to notice that the phenotypic progeny proportions indicate that the coat color phenotypes are due to segregation of alleles of one gene (ie not alleles at two different genes that affect coat color).

Using the information given above, suggest a hypothesis to explain these results. In particular, explain in your answer how many different alleles are segregating in these crosses, and the relationship between all of the alleles (ie. full dominance, incomplete dominance, co-dominance, etc). Show your work or explain your reasoning, for example by stating what a particular cross shows and how that supports your answer or argues against alternative answers.

Solution

Lets consider B1b - beige , B2b - orange , and bb - cream. From the 1st and last result , beige (B1b) x beige (B1b) gives 3/4 beige (B1b) and bb (cream). (B2b) Orange x Orange (B2b) gives 3/4 orange and 1/4 cream (bb) The above 2 results shows that beige and orange are dominant characters and cream is recessive. Similarly 2nd result B1b x bb gives 1/2 beige and 1/2 cream 3rd result shows that B2b x bb gives 1/2 orange and 1/2 cream So we can say there are 3 different alleles B1 , B2 and b participating to give different coat color. This is simple dominance and there is no codominance or incomplete dominance because the 1st and last crosses are back crosses which shows beige color and orange are dominant character.