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Unformatted text preview: 1 BICD100 Midterm (10/27/10) KEY 1. Variation in tail length is characteristic of some dog breeds, such as Pembroke Welsh Corgis, which sometimes show a bob tail (short tail) phenotype (see illustration below, left). A bob tailed male Corgi was mated with a female from a true-breeding line of long tailed Boxers. Female progeny of this cross were backcrossed repeatedly to males from the true-breeding long tailed Boxer line to generate the pedigree shown below. a. Assuming that the bob tailed trait is fully penetrant, which of the following are possible modes of inheritance for this trait? Circle all that are possible (8 pts). i. autosomal recessive ii. X-linked recessive iii. autosomal dominant iv. X-linked dominant b. Among the progeny of matings between bob tailed males and females of generation V, 1/2 had the bob tailed phenotype, 1/4 had the long tailed phenotype, and 1/4 had a tailless phenotype. Based on this and information provided earlier (do not take into account any information given later!), which of the following types of mutations could be causing the bob tailed phenotype seen in the Corgis? Circle each one that is possible (8 pts). The information in this paragraph tells you the trait is semi-dominant, not fully dominant. i. A gain of function mutation that is fully dominant to wild type ii. A gain of function mutation that is semi-dominant to wild type iii. A loss of function mutation that is recessive to wild type iv. A loss of function mutation that is semi-dominant to wild type 2 Further analysis led to the finding reported in the journal Mammalian Genome in 2001 that the bob tailed phenotype in Pembroke Welsh Corgis is due to allelic variation in the T gene, which encodes a transcription factor (a protein that binds to DNA upstream of other, so called target genes and regulates their transcription). Sequencing of T alleles determining the bob tailed phenotype revealed several differences relative to non bob tail (wild type) alleles, as summarized in the table below. Note that genes are composed of exons (which contain the protein coding information) and introns (which are spliced out of mRNA before it is translated). Change # Location of change Change in DNA sequence relative to wild type allele Effect on protein levels, gene expression pattern, and protein sequence 1 Upstream of ATG start codon A to C None 2 Intron 1 G to A None 3 Exon 1 C to G Normal gene expression pattern and protein levels, but changes isoleucine codon to methionine codon 4 Intron 2 G to A None 5 Exon 2 C to T None 6 Intron 3 T to A None 7 Intron 6 C to T None 8 Exon 8 T to C None c. Based on the information provided in this table, which of these changes could be correctly described by the term given? Put your answer on the line provided by indicating the appropriate change # shown in the table. If there is more than one possibility, then just name one. If none of the changes could be described by the term given, so state (12 pts). described by the term given, so state (12 pts)....
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