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2008midterm1B_key - BICD100 Midterm 1 KEY B 1 Variation in...

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BICD100 Midterm 1 KEY B 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 (6 pts). i. X-linked recessive ii. autosomal recessive iii. X-linked dominant iv. autosomal 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 (6 pts). i. A loss of function mutation that is semi-dominant to wild type ii. A loss of function mutation that is recessive to wild type iii. A gain of function mutation that is semi-dominant to wild type iv. A gain of function mutation that is fully dominant to wild type 1
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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. Change # Position (nucleotide #, counting the A in the ATG start codon as +1) Change in DNA sequence relative to wild type allele Effect on protein levels, expression pattern, and protein sequence 1 Upstream of coding region (-300) A to C None 2 Intron 1 (+37) C to A None 3 Intron 1 (+76) G to A None 4 Exon 1 (+295) C to G Normal protein levels and expression pattern, but changes Ile to Met 5 Intron 2 (+401) G to A None 6 Exon 2 (+511) C to T None 7 Intron 3 (+604) T to A None 8 Intron 6 (+829) C to T None 9 Exon 8 (+1171) T to C None 10 Exon 8 (+1416) C to T None c.
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