A 'wrongful birth' case was recently brought before a court in which a child with Smith–Lemli–Opitz syndrome was born to apparently healthy parents. This syndrome is characterized by a cluster of birth defects including cleft palate, and an array of problems with the reproductive and urinary organs. Originally considered by their physician as having a nongenetic basis, the parents decided to have another child, who was also born with Smith–Lemli–Opitz syndrome. In the role of a genetic counselor, instruct the court about what occurred, including the probability of the parents having two affected offspring, knowing that the disorder is inherited as a recessive trait. Draw a pedigree of the families of this couple, showing the relevant individuals.

Question

Accepted Answer

Hi, everyone. Welcome back. Here's our next problem. Examine the provided pedigree and decide which assertions about it is or are false. So we have a pedigree with just two generations and our choices are four different statements. And we're looking for the one that is false. There is no answer choice allowing more than one to be false. So presumably we have only one false statement. So let's go ahead and look at our pedigree here. Um We see that we have um in our first generation, both parents unaffected, they've had two affected Children, male and female and three unaffected Children, uh two females and one male. So with that in mind, let's look at our answer choices here. Choice. A says the trait that is being studied is recessive. Well, we see that our two affected individuals have unaffected parents that uh would lead us to believe that this would be true that the trait is recessive in a dominant trait. You would expect that all affected individuals have at least one affected parent because um they only need one allele to be affected and they must have inherited that allele from one of their parents. Uh who would then have been affected. So a cannot be our answer since it's a true statement. Joyce B says both the parents are heterozygous. Well, this is also a true statement. Uh given that we have reasons that our trait is recessive. Uh we have two affected um offspring, they must be homozygous, recessive two have since they're affected with the trait. So I'll write that and therefore, must have inherited two copies of the gene one from each parent. So both parents must be heterozygous carriers of the gene. So we will cross off choice B since that is also a true statement, cho C says affected offspring are homozygous. Well, this must also be true since we reason that our trait is recessive. So therefore to express the trait to be affected, the offspring must be homozygous recessive. So that is also not our answer choice. Since that is true. Finally, we're on to choice D which says the trait can be X length, recessive. Well, let's think about that. If it is linked recessive, that means any female who is affected must have two copies of the recessive gene. Since it's a recessive gene, she needs to be homozygous recessive and a female has two X chromosomes. However, a male who was affected has only a single X chromosome. Therefore, an affected male has only one copy of the recessive gene. If a male is unaffected, his a must be dominant, dominant and recessive. Don't really are somewhat meaningless to a male in an excellent trait since he can only express whichever all he has. So in this case, since we have an affected female, who must have inherited one X chromosome from each parent, each X would have had to have that recessive allele. If the trait were ex linked recessive, then that affected female must have had an affected father, which is not the case, her father is unaffected. So this statement is false and choice D is our answer. So again, looking at that pedigree, um the false assertion about it is choice D, the trait can be linked recessive. See you in the next video.

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Key Concepts

Recessive Inheritance

Punnett Square

Pedigree Analysis