Page 111 - Genetics_From_Genes_to_Genomes_6th_FULL_Part3

Problems 405

c. Mutations in HPRT1 are associated with two dif- 44. We think of people as having two genomes (one from
ferent syndromes. What are these syndromes? For their mother and one from their father) that are identical
each, answer the following questions: (i) What are in every somatic cell and in germ cell precursors.
the symptoms associated with the syndrome? (ii) Is However, with every DNA replication and thus every
the mutant allele that causes the syndrome domi- cell division, a genome has an opportunity to mutate.
nant, recessive, codominant, or incompletely domi- When a mutation occurs in a single cell, all of that cell’s
nant with respect to the normal allele, or do special mitotic descendants will thus have a mutation that the
conditions apply? (iii) Is the syndrome associated other cells in the body do not have. Humans are in this
with a loss-of-function or a gain-of-function dis- sense mosaic—we are a patchwork of cells with some-
ease allele? (iv) Does the syndrome display allelic what different genotypes. Explain how human mosa-
heterogeneity? (v) Does the syndrome display lo- icism could complicate the process of pinpointing a
cus heterogeneity? (Note: You do not need to un- recessive or dominant disease-causing mutation by po-
derstand everything in the OMIM entries to answer sitional cloning or by genome sequencing.
these questions.)