6. All the offspring of a white hen and a black rooster are gray. The sim- plest
ID: 136155 • Letter: 6
Question
6. All the offspring of a white hen and a black rooster are gray. The sim- plest explanation for this pattern of inheritance is a. pleiotropy. b. sex linkage. c. codominance. d. incomplete dominance. 7. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes? (Hint: Review Figure 9.20.) a. A, B, or O b. AB only c. AB or O d. A, B, AB, or O 8. Duchenne muscular dystrophy is a sex-linked recessive disorder char- acterized by a progressive loss of muscle tissue. Neither Rudy nor Carla has Duchenne muscular dystrophy, but their first son does have it. If the couple has a second child, what is the probability that he or she will also have the disease? 9. Adult height in people is at least partially hereditary; tall parents tend to have tall children. But people come in a range of sizes, not just tall or short. What extension of Mendel's model could produce this variation in height?Explanation / Answer
6) Option 'd' is the correct answer.
The case given in the question is an example of incomplete dominance in which neither the allele for black color is dominant nor the allele for white color, i.e., both thr traits are not expressed compltely over the other. The result is a third phenotype of intermediate grey color which is a combination of both the alleles for black and white color.
7) Option 'd' is the correct answer.
If the genotype of mother and father for A and B blood types is IaIo and IbIo respectively, then the possible genotypes are given in the punnet square as follows:
8) Duchenne muscular dystrophy is an X-linked disease, therefore the presence of only one diseased allel in males is sufficient to produce the symptoms of disease, while females with one affected allele act as carriers for the disease while themselves not showing any symptom of the disease.
In case of Rudy and Carla, their first son suffers from muscular dystrophy, hence it stands to reason that the diseased X-allele must come from one of the parents. Since, it is already given that both Rudy and Carla are phenotypically normal and disease free and since muscular dystrophy is a sex linked disease and the presence of diseased allele in male will produce symptoms, therefore we can conclude that Carla, i.e, mother must be the carrier of disease. Hence, the genotype of the parents will be XY for father and XX for mother, where X represents the diseased allele.
The possible genotypes of their second child can be predicted as follows:
Therefore, there is a 25% probability that the second child of Rudy and Carla will suffer from Duchenne muscular dystrophy.
9) Inheritance of human height is an example of polygenic inheritance, i.e, height is not controlled by just one gene, rather it is a result of expression of multiple genes and their traits. When there are large number of genes involved, it becomes hard to distinguish the contribution of one single gene. There is an additive effect of the traits of multiple genes. Other than that, environmental factors such as nutrition also play a role in determining a person's height.
Parental alleles Ia Io Ib IaIb = AB blood type IbIo = B blood type Io IaIo = A blood type IoIo = O blood typeRelated Questions
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