ch04_review Questions

ch04_review Questions - CHAPTER 4 1 REVIEW QUESTIONS True...

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CHAPTER 4   REVIEW QUESTIONS 1. True or false? A wild-type allele corresponds to the allele that is responsible for the normal  phenotype and is always dominant. HINT: Alleles are alternative forms of genes that influence a phenotype. False. The wild-type allele is designated arbitrarily to identify the normal phenotype and is  often, but not necessarily, dominant.  4.1 Alleles Alter Phenotypes in Different Ways (p. 67) 2. In incomplete dominance, heterozygotes have a phenotype that is HINT: Incompletely dominant alleles produce novel phenotypes in the heterozygous  condition. a. Characteristic of both homozygous phenotypes Incorrect. Alleles producing this phenotype show  codominance 4.3 In Incomplete  Dominance, Neither Allele Is Dominant (p. 68) b. Not clearly like either homozygous phenotype Correct. Alleles showing incomplete dominance produce heterozygotes that have an  intermediate phenotype between the homozygous phenotypes.  4.3 In Incomplete  Dominance, Neither Allele Is Dominant (p. 68) c.Indistinguishable from the homozygous phenotypes Incorrect. Alleles producing this phenotype show  complete dominance 4.3 In  Incomplete Dominance, Neither Allele Is Dominant (p. 68) d. More environmentally influenced than the phenotypes of the homozygotes Incorrect. This situation is extremely rare.  4.3 In Incomplete Dominance, Neither Allele  Is Dominant (p. 68) 3. Some cases that appear to exhibit complete dominance may really be cases of incomplete  dominance. What is the evidence for this statement? HINT: Consider the enzyme hexosaminidase A in Tay-Sachs disease. a. Hybrids exhibit both phenotypes. Incorrect. This is the definition of  codominance 4.3 In Incomplete Dominance, Neither  Allele Is Dominant (p. 68) b. Hybrids show an intermediate phenotype. Incorrect. This is the definition of  incomplete dominance  rather than complete  dominance.  4.3 In Incomplete Dominance, Neither Allele Is Dominant (p. 68) c.Quantitative analysis of the level of gene product indicates that hybrids produce an  intermediate amount. Correct. Analysis of the level of gene product often reveals an intermediate level of  gene expression in heterozygotes, even when they exhibit the dominant phenotype.  4.3 In Incomplete Dominance, Neither Allele Is Dominant (p. 68)
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d. The homozygous recessives show the recessive phenotype. Incorrect. This would be true whether the alleles showed complete dominance,  incomplete dominance, or codominance.  4.3 In Incomplete Dominance, Neither Allele  Is Dominant (p. 68) 4. True or false? Heterozygotes of single locus traits with codominant alleles produce a 1:2:1  phenotypic ratio in Mendelian crosses.
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