CHEM 237 finalkey - Final Exam Key, GENOME 371 Autumn 2005...

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Final Exam Key, GENOME 371 Autumn 2005 Berg/Brewer 1A. (4 pts) 1A. (4 pts) d. sex-linked recessive b. autosomal recessive Define notation: Derma = X d ; normal = X D Define notation: Freckles = f; no freckles = F I-1 X D X d I-1 Ff II-3 X d Y II-3 F? III-8 X D X d III-8 Ff IV-4 X D X ? IV-4 F? 1B. (4 pts) 1B. (4 pts) b. autosomal recessive d. sex-linked recessive Define notation: Freckles = f; no freckles = F Define notation: Derma = X d ; normal = X D I-1 Ff I-1 X D X d II-3 F? II-3 X d Y III-8 Ff III-8 X D X d IV-4 F? IV-4 X D X ? 1C. (5 pts) 5 cM Xe7 D F 25 cM (between 20 and 30 cM) 15 cM (between 10 and 22 cM) D and F are more than 20 cM apart 5 cM Xe7 25 cM (between 20 and 30 cM) 15 cM (between 10 and 22 cM) D F D and F are more than 20 cM apart 1D. (3 pts) Pedigree analysis reveals that Freckles is autosomal and Derma is sex-linked, yet the marker Xe7 is linked to both. This conflicting information can be resolved by realizing that Freckles resides on the pseudosutosomal region of the X and Y, while Derma is in the X-specific portion of the X. Freckles therefore behaves as if it were an autosomal gene—showing no differences in males and females, while Derma shows the classic signs of being X-linked and not having an allele on the Y. (Most people decided that Xe7 was a bad marker—that is, repeated in the genome. Repeated molecular markers are not used in mapping so this answer was not an entirely satisfactory answer.)
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2A . (4 pts) Based on the maps of the wild type and orange alleles, the orange allele appears to be a deletion mutation. It could have occurred through improper recombination (or crossing-over) between misaligned retrotransposons on homologues or on sister chromatids, or by intrachromosomal recombination between the two retrotransposons on the same chromatid. 2B. (4 pts) To determine if the orange allele is dominant or recessive we need to test the phenotype of a heterozygous cell and ask whether that cell makes orange pigment or black pigment. Since the Orange locus is on the X chromosome and is subject to random X-chromosome inactivation, no cell in the heterozygous cat is actually expressing both alleles at the same time. 2C.
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CHEM 237 finalkey - Final Exam Key, GENOME 371 Autumn 2005...

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