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Chapter 3: Problem 14

Dentinogenesis imperfecta is a rare, autosomal, dominantly inherited disease of the teeth that occurs in about one in 8000 people (Witkop 1957 ). The teeth are somewhat brown in color, and the crowns wear down rapidly. Assume that a male with dentinogenesis imperfecta and no family history of the disease marries a woman with normal teeth. What is the probability that (a) their first child will have dentinogenesis imperfecta? (b) their first two children will have dentinogenesis imperfecta? (c) their first child will be a girl with dentinogenesis imperfecta?

Short Answer

Expert verified
Answer: The probabilities are as follows: (a) 50%, (b) 25%, and (c) 25%.

Step by step solution

01

Determine the genotypes of the parents

The father has dentinogenesis imperfecta, so his genotype is Dd. The mother does not have dentinogenesis imperfecta, so her genotype is dd.
02

Create a Punnett Square

We will create a 2x2 Punnett square to determine the possible genotypes of their children. ``` D d _________ d| Dd | dd | _________ d| Dd | dd | _________ ```
03

Calculate the probability for (a) their first child will have dentinogenesis imperfecta?

From the Punnett square, we can see that there are 4 possible outcomes, and 2 of them (the two Dd boxes) represent children that will have dentinogenesis imperfecta. So, the probability that their first child will have dentinogenesis imperfecta is 2/4, which simplifies to 1/2 or 50%.
04

Calculate the probability for (b) their first two children will have dentinogenesis imperfecta?

Since the probability of each child having dentinogenesis imperfecta is independent, we only need to multiply the probability of the first child having the disease (1/2) by the probability of the second child having the disease (1/2). Doing so, we get a probability of (1/2) * (1/2) = 1/4 or 25%.
05

Calculate the probability for (c) their first child will be a girl with dentinogenesis imperfecta?

In order to answer this question, we need to take into account the sex of the child. The probability of having a girl or a boy is 1/2. So, the probability of having a child with dentinogenesis imperfecta (1/2) must be multiplied by the probability of having a girl (1/2). This yields a probability of (1/2) * (1/2) = 1/4 or 25%.

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Most popular questions from this chapter

Tay-Sachs disease (TSD) is an inborn error of metabolism that results in death, often by the age of \(2 .\) You are a genetic counselor interviewing a phenotypically normal couple who tell you the male had a female first cousin (on his father's side) who died from TSD and the female had a maternal uncle with TSD. There are no other known cases in either of the families, and none of the matings have been between related individuals. Assume that this trait is very rare. (a) Draw a pedigree of the families of this couple, showing the relevant individuals. (b) Calculate the probability that both the male and female are carriers for TSD. (c) What is the probability that neither of them is a carrier? (d) What is the probability that one of them is a carrier and the other is not? [Hint: The \(p\) values in (b), (c), and (d) should equal \(1 .]\)

What is the basis for homology among chromosomes?

Two organisms, \(A A B B C C D D E E\) and aabbccddee, are mated to produce an \(\mathrm{F}_{1}\) that is self-fertilized. If the capital letters represent dominant, independently assorting alleles: (a) How many different genotypes will occur in the \(\mathrm{F}_{2}\) ? (b) What proportion of the \(\mathrm{F}_{2}\) genotypes will be recessive for all five loci? (c) Would you change your answers to (a) and/or (b) if the initial cross occurred between \(A A b b C C\)ddee\(\times\)aaBBccDDEE parents? (d) Would you change your answers to (a) and/or (b) if the initial cross occurred between \(A A B B C C D D E E \times\) aabbccddEE parents?

Assume that Migaloo's albinism is caused by a rare recessive gene. (a) In a mating of two heterozygous, normally pigmented whales, what is the probability that the first three offspring will all have normal pigmentation? (b) What is the probability that the first female offspring is normally pigmented? (c) What is the probability that the first offspring is a normally pigmented female?

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.) (a) Two normal parents have five children, four normal and one albino. (b) A normal male and an albino female have six children, all normal. (c) A normal male and an albino female have six children, three normal and three albino. (d) Construct a pedigree of the families in (b) and (c). Assume that one of the normal children in (b) and one of the albino children in (c) become the parents of eight children. Add these children to the pedigree, predicting their phenotypes (normal or albino).
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