5. Incomplete dominance & Co-dominance, Scenario 1 – Ear spotting – Jaguars show

Question

5. Incomplete dominance & Co-dominance, Scenario 1 – Ear spotting – Jaguars show spotting patterns on the inner fleshy part of their ears. The SZ allele causes square spots at the tip of the inner portion of the ear and SW allele causes egg-shaped spots at the base of the inner portion of the ear. Individuals are found in the population that have both types of spots, how can this be explained? Scenario 2 – Apple seed number – the number of apple seeds per apple is a single-gene trait. The wild-type gene produces a protein that directly affects the number of seeds produced in a single apple. A frameshift mutation in the coding region of this gene leads to a truncated and non-functional protein. Apple trees that are heterozygous for this gene, have a fewer number of seeds in each apple than wild type but more than the homozygous mutant, how can this be explained? Scenario 3 – Smurfs – Even though we all know from television that Smurfs are solid blue, the program creators curiously hid the fact that there are also solid yellow, green and white Smurfs occurring in most Smurf populations (Note: it is not known why the creators of the show did not disclose this heterogeneity in the population, but “60 minutes” is investigating it). In some matings of blue and yellow smurfs, green smurf offspring will result. When white smurfs mate, only white smurf offspring are created, how can this be explained? Linked and Un-linked genes and crossing-over. THE FOLLOWING 2 QUESTIONS ARE OPTIONAL, BUT STRONGLY ENCOURAGED, ie they will not be graded. 1. In peas, round (R) pea coats are dominant over wrinkled (r) pea coats and yellow-colored (Y) peas are dominant over green-colored (y) peas. A true-breeding round/yellow pea plant is crossed with a wrinkled/green pea plant. The offspring of this cross (the F1) are then crossed with a new wrinkled/green pea plant and this yielded the following offspring results: 252 round / yellow 248 round / green 244 wrinkled / yellow 255 wrinkled / green What is the most likely explanation for this pattern of inheritance? Show your work to justify your answer. Is that the only explanation? 2. In rabbits, black (B) is dominant to brown (b), while straight fur (S) is dominant to curly (s). The genes controlling these traits are linked. Many rabbits that are heterozygous (created by crossing two pure-breeding lines – black/straight & brown/curly) for both traits and express black / straight, were crossed with many rabbits that express brown / curly (double-recessive for both characters) and yielded the following total number of offspring: 31 brown / curly 35 black / straight 16 brown / straight 19 black / curly What is the most likely explanation for this pattern of inheritance? Show your work to justify your answer. The next one is optional but worthwhile - Determine the arrangement of alleles in the heterozygous parent and map the distance between the two genes.

Explanation / Answer

1. The different phenotypic combinations appear in nearly equal proportion- round/yellow- 252; round/green- 248; wrinkled/ yellow- 244; wrinkled/ green- 255

This is incomplete dominance, a condition where both alleles of a gene get expressed and there is no mixing of the effect of the alleles. The resultant phenotype is a combination of the parental phenotypes.

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