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Ptosis is a weakness in the muscles of the eyelid - VCE - SSCE Biology - Question 2 - 2004 - Paper 1
Question 2
Ptosis is a weakness in the muscles of the eyelid. a. Using the information in the text box below, construct a pedigree to fit the description of the inheritance of... show full transcript
Worked Solution & Example Answer:Ptosis is a weakness in the muscles of the eyelid - VCE - SSCE Biology - Question 2 - 2004 - Paper 1
Step 1
a. Construct a pedigree to fit the description of the inheritance of ptosis in the family.
Answer
To construct the pedigree, begin by representing each individual according to their condition. Since Bill has ptosis, he is represented with a filled symbol. His wife Jill, who does not have ptosis, is represented with an unfilled symbol. Their children Ben (unaffected) and Daisy (affected) are represented accordingly. Daisy's husband Bob, who does not have ptosis, is also unfilled, and their daughters are depicted with two filled symbols (for the two girls with ptosis) and one unfilled symbol (for the girl without ptosis). Ensure that the lineage connecting these individuals is clearly drawn to represent the family structure.
Step 2
b.i. Based on the information in this pedigree, what is the most likely mode of inheritance of ptosis?
Answer
The most likely mode of inheritance of ptosis in this pedigree is autosomal dominant. This conclusion is based on the observation that individuals with the condition can be found in every generation, and the presence of both males and females being affected suggests equal likelihood of inheritance regardless of sex.
Step 3
b.ii. Provide two pieces of evidence from the pedigree that support this conclusion.
Answer
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In the pedigree, the affected individuals (filled symbols) can be traced back to an affected parent, clearly showing that the trait is passed from parent to offspring.
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Both the daughters of Daisy show the condition, indicating that as long as one parent carries the allele for ptosis, the children have a probability of expressing the condition, which is characteristic of an autosomal dominant trait.