Lecture 4 1. Different alleles of a gene • usually all result in the same phenot

Question

Lecture 4

1. Different alleles of a gene

• usually all result in the same phenotype

• may result in a wide variety of phenotypes

• can complement to produce a wildtype hybrid

• are usually null mutations

2. One of the necessary conditions for a recessive lethal to be identified is that

• it also have a dominant morphological effect

• it interact with other genes that are not lethal

• some homozygotes are able to survive

• none of these are necessary

3. If a man with blood type A marries a woman with blood type B, which of the following blood types could not occur in their offspring?

• O

• AB

• A

• all could occur

4. Which of the following phenotypic ratios reflects incomplete dominance?

• 3:1

• 1:1

• 2:1

• 1:2:1

5. At which of the following levels will expression of the sickle cell gene be observed as a completely dominant trait?

• organismal - the presence of anemia under certain environmental conditions

• cellular - the shape of the red blood cell under certain environmental conditions

• protein - the structure of the hemoglobin molecules

• all of these

6. Which of the following would best characterize a conditional mutation?

• inability to develop normal wings at 250 C, normal development at 180C

• inability to synthesize the vitamin biotin at any temperature

• a reduction in the number of eye facets

• inability to fly at 290C, normal flying ability regained at 210C.

7. In a complementation test, a cross between two different mutants in the same gene will produce offspring with a _____ phenotype, and a cross between two different mutants in different genes will produce offspring with a _____ phenotype.

• wildtype; mutant

• mutant; wildtype

• mutant; unpredictable

• neither outcome will be consistently predictable

Explanation / Answer

1. Different alleles of a gene- may result in a wide variety of phenotypes

2. One of the necessary conditions for a recessive lethal to be identified is that it also have a dominant morphological effect

3. If a man with blood type A marries a woman with blood type B, which of the following blood types could not occur in their offspring? all could occur

Which of the following phenotypic ratios reflects incomplete dominance? 1:2:1

At which of the following levels will expression of the sickle cell gene be observed as a completely dominant trait? All of these

Which of the following would best characterize a conditional mutation- inability to fly at 290C, normal flying ability regained at 210C

In a complementation test, a cross between two different mutants in the same gene will produce offspring with a __mutant___ phenotype, and a cross between two different mutants in different genes will produce offspring with a __wildtype___ phenotype.

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