MIT Department of Biology 7.013: Introductory Biology - Spring 2005 Instructors: Professor Hazel Sive, Professor Tyler Jacks, Dr. Claudette Gardel NAME_______________________________________________________________TA________ 7.013 Spring 2005 Problem Set 2 FRIDAY February 18, 2004 Problem sets will NOT be accepted late. Question 1 The following family was used to study the transmission of a gene responsible for a rare trait. Since the trait is 'rare', assume that people marrying into the family have 2 normal alleles for the gene of interest in this case. This family was found to carry the rare allele manifesting in the ability to see through walls (“x-Ray vision”). The pedigree for this phenotype follows. 1 2 3 4 5 female male Normal vision x-Ray vision a) What is the most likely mode of inheritance? (Choose from: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked dominant, and Y-linked recessive, or mitochondrial inheritance.) b) Use “R” and “r” for the x-Ray vision alleles. Use the capital letter for the allele conferring the dominant phenotype and include sex chromosomes if appropriate. What is the genotype of individual 2? c) What is the genotype of individual 3? d) If individual 4 marries individual 5, what is the probability that their child will be heterozygous at the locus of interest? Show your work. 1Amazingly (and conveniently), the same family carries the rare allele for having 6 fingers. The inheritance pattern follows. The inheritance patterns for both the 6-finger phenotype and x-Ray vision are illustrated in the following pedigree. 1 2 3 4 5 6 fingers x-Ray vision Both x-Ray vision and 6 fingers e) What is the most likely mode of inheritance for the allele causing the 6-finger phenotype? (Choose from: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked dominant, and Y-linked recessive, or mitochondrial inheritance.) f) If the genes conferring x-Ray vision and having 6 fingers are linked, what alleles of the two genes are found on each chromosome of individual #1, IF NO recombination occurs,? Use “D” and “d” to describe the alleles of the finger or Digit locus. Use “R” and “r” to describe the alleles of the x-Ray locus. Use the capital letter for the allele conveying the dominant phenotype. Place the alleles for each locus on the chromosomes shown below. Indicate whether the chromosomes below are sex chromosomes. Individual #1 one chromosome other matching chromosome digit locus x-Ray vision locus 2Question 2 Near the halls approaching the BioCafe, you discover a colony containing amazing never before seen glow-in-the-dark cockroaches. Curious as to how this trait is inherited, you observe the progeny descended from one particular glow-in-the-dark cockroach over several generations. 2 1 3 ? 4 5 ? normal male glow-in-the-dark male normal female glow-in-the-dark female a) What is the most likely mode of inheritance of the glow-in-the-dark trait? (Choose from: autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked dominant, and Y-linked recessive, or mitochondrial inheritance.) b) Using “R” for the dominant allele and “r” for the recessive allele, and sex chromosomes if appropriate, what is the genotype of: Cockroach # 1? _____________ Cockroach # 2? _____________ Cockroach # 3? _____________ c) What is the probability that Cockroach # 4 will glow in the dark? If male ________________________If female__________________________ d) What is the probability that Cockroach #5 will glow in the dark? If male ________________________If female__________________________ 3Question 3 In the year 2012, a Mars probe sends a Martian soil sample back to Earth. Your lab is chosen to study an organism found alive in this sample! The organism contains DNA that uses the same 4 deoxyribonucleotides (dGTP, dATP, dTTP, and dCTP) that earth organisms use. You isolate the Martian DNA polymerase so you can study DNA replication in this organism. You use Martian DNA polymerase, a short DNA primer (5’ ACCCAG 3’) (DNA primers work as well as RNA primers) and the 4 deoxyribonucloetides to replicate the following double stranded DNA template. 10 20 30 40 | | | | 5’–ACTTGATGGGGCATAACGCTACCTGGGTCCGATACAGTTT-3’ 3’–TGAACTACCCCGTATTGCGATGGACCCAGGCTATGTCAAA-5’ a) In what direction does DNA polymerization occur on Earth? 3’5’ CN 5’3’ NC b) If the Martian DNA polymerase synthesizes DNA in the 5’ to 3’ direction, write the resulting DNA sequences and indicate the polarity (5’ and 3’) and the lengths (in nucleotides) of the daughter strand(s) on the figure below. 5’ –ACTTGATGGGGCATAACGCTACCTGGGTCCGATACAGTTT- 3’ 3’ –TGAACTACCCCGTATTGCGATGGACCCAGGCTATGTCAAA- 5’ c) Based on your answer and the primer provided, will you be able to fully replicate the Martian DNA boxed above? If no, explain why not. 4c) Meselson and Stahl demonstrated that E. colireplicates in a distinct manner. (See textbook, pgs 221-222.) This was shown by first growing E. coliin medium containing 15N for the first few generations, shifting the culture to medium containing to lighter 14N and then examining the density of the next generation of DNA. Their results are shown below. lightlight heavyheavy parental 1st generation after shift 2nd generation after shift i) What manner of replication did they observe? Conservative, Semi-conservative or Dispersive? ii) You perform the same kind of experiment with your Martian organism and you get the following results. What manner of replication is this? Conservative, Semi-conservative or Dispersive? parental 1st generation after shift 2nd generation after shift 5Question 4 While working in the lab late one night, you notice something about the mice that live behind the freezers: Most of the mice are black, but there are rare cases of white mice. You capture two white mice and two black mice, and breed black with black and white with white. You find that all of the offspring of the black mice are black, and all of the offspring of the white mice are white. You find these strains to be pureor true breeding, that is to say all subsequent generations resemble their parents with respect to fur color. a) One of the white males gets tired of the local scene and sneaks out of his cage and into a cage full of black females. The next morning, you find him sleeping in the corner. After putting him
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