Question

Questions 1-4

1. DNA polymerase I is thought to add nucleotides ________.

		in the place of the primer RNA after it is removed
		to the 5' end of the primer
		to the 3' end of the primer
		on single-stranded templates without need for an RNA prime

2.

In individuals affected with Tay-Sach' s disease, there is almost no activity of an enzyme called hexosaminidase A. Heterozygotes, with only a single copy of the mutant gene, have 50% enzyme function but are phenotypically normal. This illustrates ______.

		Genetic anticipation
		The Threshold Effect
		Codominance
		Multifactorial inheritance
		Dominance

3.

wo recessive mutations that cause a "wingless" mutation in Drosophila are independently isolated. A researcher wonders whether the mutations are in the same gene or different genes, so he crosses the two strains. The outcome is that all offspring develop normal wings. Restoration of the wild-type phenotype is due to _________.

		Genomic imprinting
		Methylation
		Complementation
		X-linked inheritance

4.

For some genetic disorders, the expression of the phenotype depends on whether an allele is inherited from the mother or father. An example in mice occurs with a gene for insulin-like growth factor II (Igf2): a heterozygous mouse will be dwarf if its normal allele comes from his mother and its mutant allele comes from his father. This is an example of _________.

		Genomic imprinting
		Maternal inheritance
		Sex-influenced inheritance
		Sex-limited inheritance
		Sex-influenced inheritance

Answer 1

1. DNA polymerase I is thought to add nucleotides to the 3' end of the primer because DNA strand always extends in 5' to 3' direction.

2. In individuals affected with Tay-Sach' s disease, there is almost no activity of an enzyme called hexosaminidase A. Heterozygotes, with only a single copy of the mutant gene, have 50% enzyme function but are phenotypically normal. This illustrates Dominance of the alleles of enzyme.

3. wo recessive mutations that cause a "wingless" mutation in Drosophila are independently isolated. A researcher wonders whether the mutations are in the same gene or different genes, so he crosses the two strains. The outcome is that all offspring develop normal wings. Restoration of the wild-type phenotype is due to Complementation of the alleles.

4. For some genetic disorders, the expression of the phenotype depends on whether an allele is inherited from the mother or father. An example in mice occurs with a gene for insulin-like growth factor II (Igf2): a heterozygous mouse will be dwarf if its normal allele comes from his mother and its mutant allele comes from his father. This is an example of Sex-limited inheritance as only the male allele is responsible for the normal phenotype in this case.