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Dyskeratosis congenita (DKC) is a rare genetic disorder characterized by abnormal fingernails and skin pigmentation, the formation of white patches on the tongue and cheek, and progressive failure of the bone marrow. An autosomal dominant form of DKC results from mutations in the gene that encodes the RNA component of telomerase. Tom Vulliamy and his colleagues examined a series of families with autosomal dominant DKC (T. Vulliamy et al. 2004. Nature Genetics ). They observed that the median age of onset of DKC in parents was 37 years, whereas the median age of onset in the children of affected parents was 14.5 years. Thus, DKC in these families arose at progressively younger ages in successive generations, a phenomenon known as anticipation (see Chapter 5). The researchers measured the telomere lengths of members of these families; the measurements are given in the accompanying table. Telomeres normally shorten with age, so telomere length was adjusted for age; the values given in the table are the differences between the actual length and the expected length based on age. Note that the values of all members of these families are negative, indicating that their telomeres are shorter than normal for their age; the more negative the number, the shorter the telomere.a. How does the telomere length of the parents comparewith the telomere length of the children? (Hint:Calculate the average telomere length of all parentsand the average telomere length of all children.)b. Explain why the telomeres of people with are shorter than normal.c. Explain why DKC arises at an earlier age in subsequent generations.

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Dyskeratosis congenita (DKC) is a rare genetic disorder characterized by abnormal fingernails and skin pigmentation, the formation of white patches on the tongue and cheek, and progressive failure of the bone marrow. An autosomal dominant form of DKC results from mutations in the gene that encodes the RNA component of telomerase. Tom Vulliamy and his colleagues examined a series of families with autosomal dominant DKC (T. Vulliamy et al. 2004. Nature Genetics ). They observed that the median age of onset of DKC in parents was 37 years, whereas the median age of onset in the children of affected parents was 14.5 years. Thus, DKC in these families arose at progressively younger ages in successive generations, a phenomenon known as anticipation (see Chapter 5). The researchers measured the telomere lengths of members of these families; the measurements are given in the accompanying table. Telomeres normally shorten with age, so telomere length was adjusted for age; the values given in the table are the differences between the actual length and the expected length based on age. Note that the values of all members of these families are negative, indicating that their telomeres are shorter than normal for their age; the more negative the number, the shorter the telomere.a. How does the telomere length of the parents comparewith the telomere length of the children? (Hint:Calculate the average telomere length of all parentsand the average telomere length of all children.)b. Explain why the telomeres of people with are shorter than normal.c. Explain why DKC arises at an earlier age in subsequent generations.
TopicAll topics
SubjectBiology
ClassClass 11