In a hypothetical diploid organism, “squareness” of a cell is due to a threshold

Question

In a hypothetical diploid organism, “squareness” of a cell is due to a threshold effect (gene product levels are important): more than 60 activity units of "square factor" per cell produces a “square” phenotype while less than 60 activity units produces a “round” phenotype. square (s) is a gene that controls the synthesis of square factor. The most common allele found in nature is sc. This allele contributes 50 units of square factor, thus, sc homozygotes have 100 units and are phenotypically square. sn is a null allele (no functional gene product made). sn homozygotes are phenotypically round. A final mutant allele, sh, contributes 70 units of square factor. Sh homozygotes have 140 units and are phenotypically square.

a. The Sc allele is also known as the ________________ allele (insert term).

b. Recall the Sn is a null allele. How many activity units of square factor is made within Sn homozygotes. _______________

c. Describe the expected dominance relationship between sc and sn alleles? Explain your answer. In your explanation, use ALL the terms listed on the next page that apply.

d. Describe the dominance relationship between, sh and sn alleles? Explain your answer. In your explanation, use ALL the terms listed below that apply.

           recessive           haploinsufficinet

           dominant           haplosufficient  

           semidominant codominant

Explanation / Answer

a. Haploinsufficient

b. No activity units can be measured as the product is a non functional protein.

c. sc allele appears to be dominant over sn allele as sc allele produces a functional gene product (50 units of square factor) leading to a square phenotype, whereas sn is a null allele with no functional gene product. However, sc is a haploinsufficient allele as both the allele products are required for the phenotype.

d. sh is dominant over sn allele. The logic behind this explaination is that sh produces a functional product (70 units of square factor) and sn being a null allele does not produce a functional product at all.

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