Chapter 6 Answers

    1. These are four common terms that are often used interchangeably by novice students, but do have distinctly different meanings and uses.
      1. gene = general term for a segment of nucleic acid that is responsible for one or more phenotypes
      2. locus = the position of a gene along a chromosome,
      3. allele = the form (DNA sequence) of a gene at a locus,
      4. transcription unit = the segment of DNA that is transcribed into RNA (often mRNA in the case of a protein coding gene).
    2. Form (1) RR (red) x rr (white) gives Rr (red progeny).  “R” is dominant to “r”.  Form (2)  r+r+ (red) x r-r- (white) gives r+r- (red progeny). “r+” is dominant to “r-”.  For pink progeny, the symbols are the same, only “R” or “r+” is semi-dominant to “r” or “r-”.
    3. If your blood type is B, then your genotype is either IBi or IBIB. If your genotype is IBi, then your parents could be any combination of genotypes, as long as one parent had at least one i allele, and the other parent had at least one IB If your genotype was IB IB, then both parents would have to have at least one IB allele.
    4. case 1 co-dominance; case 2 incomplete-dominance; case 3 incomplete penetrance; case 4 pleiotropy; case 5 haplo-sufficiency; case 6 haplo-insufficiency; case 7 broad (variable) expressivity
      • Mutant#1 = hypomorph;
      • Mutant#2 = hypermorph;
      • Mutant#3 = amorph;
      • Mutant#4 = neomorph;
      • Mutant#5 = antimorph


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