lecture_14__05 - The J locus controls the production of a...

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The J locus controls the production of a metabolic enzyme that has several variants. The J 1 allele makes variant 1, J 2 makes variant 2, and the j allele makes no enzyme. J 1 is dominant over J 2 and both J 1 and J 2 are dominant over the j allele. What would be the phenotypic ratios of offspring from a cross between J 1 j and J 2 j ? A. 50% variant 1, 50% variant 2 B. 50% variant 1, 25% variant 2, 25% no enzyme produced C. 25% variant 1, 50% variant 2, 25% no enzyme produced D. 50% variant 1, 50% no enzyme produced E. 100% no enzyme produced If a cross if performed between two parental strains that produces ~50% variant 1 progeny and ~50% variant 2 progeny, what can you conclude about the genotype of the parental strains? A. The parents were both heterozygous J 1 J 2 B. The parents were J 1 J 2 and J 1 j C. The parents were J 1 j and J 2 J 2 D. Either B or C E. Either A, B, or C
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? What kinds of mutations cause dominant vs. recessive disorders? Different classes of mutations that occur in cells: point mutations insertions and deletions large-scale chromosomal rearrangements Where do mutations come from? Genetically distinct alleles are usually inherited from a parent, or formed during meiotic recombination. Mutations can also arise in the form of DNA damage that occurs in somatic cells or in germ cells, but only germ cell mutations are passed on to future generations.
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Point mutations = single base-pair changes in DNA sequence Point mutations can be either in the coding region of a gene, or outside the coding region A point mutation in a coding region can lead to: A) no change in protein sequence,also known as a silent mutation B) a change from one amino acid to another, also known as a missense mutation C) a change from an amino acid to a stop codon, also known as a nonsense mutation Example: mutation of a GUG codon to GUU does not result in a change in protein sequence and is therefore 'silent' since GUU, GUC, GUG, and GUA all code for valine Example: mutation of a GUG codon to GAG results in a change from a valine residue to a glutamate residue and is thus a 'missense' mutation the effects of the mutation depends on many different factors: where the amino acid is in the three-
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This document was uploaded on 09/06/2009.

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lecture_14__05 - The J locus controls the production of a...

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