In human gestational development, abnormalities of the closure of...

Question

In human gestational development, abnormalities of the closure of the lower part of the mid-face can result in cleft lip, if the lip alone is affected by the closure defect, or in cleft lip and palate (the roof of the mouth), if the closure defect is more extensive. Cleft lip and cleft lip with cleft palate are multifactorial disorders that are threshold traits. A family with a history of either condition has a significantly increased chance of a recurrence of mid-face cleft disorder in comparison with families without such a history. However, the recurrence risk of a mid-face cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone.

Construct a similar explanation of why the recurrence risk of a cleft disorder is higher in families with a history of cleft lip with cleft palate than in families with a history of cleft lip alone.

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together. Suppose an individual has congenital hip dysplasia in which there is a misalignment in the upper leg, bone ball with its socket on the hip. Considering that this phenotype is a threshold trait who among the following is likely to be affected by this trait. The answer options are a grandparents, b cousins, c siblings and D in-laws. Now recall that a threshold trait is a polygenic or multifactorial treat. And I like to think of them as an all or nothing trait. Either the individual will have congenital hip dysplasia as in this problem or they will not. Now, in threshold traits, the phenotype is determined by a lies with varying genetic liabilities. So the ayes have varying genetic liabilities. Now, what does that mean an individual may have certain allys that can push the phenotype past this threshold of liability or pass that line that determines the all or nothing, meaning certain allys may contribute more than others. And once that threshold of liability is met, the individual would then have congenital hip dysplasia. Now, the chance of an individual having congenital hip dysplasia is determined by their genotype. Therefore, someone who is likely to be affected by this trait would share similar DNA to the individual. Now, siblings share approximately 50% of the same DNA. So the correct answer is option c siblings. All right, everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

Key Concepts

Multifactorial Inheritance

Threshold Traits

Familial Aggregation

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