Bio 97 Peer Tutor W3.doc

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Biological Sciences
Rahul Warrior

Tutor: Christina Phan Week 3 Worksheet Bio 97: Warrior/Cinquin/Bardwell OH: Wednesday, 12-2 PM, SH 149 [email protected] 1. What is epigenetics? Give 2 examples of epigenetics? Study of DNA modification that affects gene expression 1. Histone modification: - Acetylation: removes (+) charge  increase gene transcription - Methylation: leaves charge intact - Phosphorylation: adding negative charge  DNA more accessible 2. Methylation of cytosine residues on DNA  blocks transcription - CpG islands: frequency of C-G base pairs is higher than in any other stretches of DNA 2. How might epigenetics account for observed differences between identical twins? Environment can affect identical twins - life style choices 3. Determine whether each Punnett square is being performed by test cross/back cross or reciprocal cross? _______Test cross _______________ ________Reciprocal ______________ Test cross: unknown x homozygous recessive parent - Aa Reciprocal cross: 2 different crosses are done with the same trait - identical results in both crosses - Aa Back cross: offspring from F1is crossed with its parent 4. If you fertilized a purebred dominant with a purebred recessive, what are the F2 phenotype ratios? F1 phenotype ratios? F2 genotype ratios? F1 genotype? Parent: AA x aa A: tall ; a: short F 1 4:0 (Aa)  tall F 2 1:2:1(AA: Aa: aa)  3 tall and 1 short Tutor: Christina Phan Week 3 Worksheet Bio 97: Warrior/Cinquin/Bardwell OH: Wednesday, 12-2 PM, SH 149 [email protected] 5. In mice, black is dominant over tan and short tails are dominant over long. • Use B for black and b for tan; Use S for short and s for long. • Write the genotype for a heterozygous black, short-tailed mouse. • Cross two of these individuals. • From the Punnett Square, describe the phenotype of the offspring. 9 black and short 3 black and long 1 tan and long 3 tan and short Dihybrid cross ONLY produce phenotypes (cannot tell if it is recessive or dominant) 6. Which of the following shows the pedigree for a recessive allele? True or False: In general for pedigrees of the recessive allele, those who are affected have parents that are affected. FALSE True or False: For both the dominant and recessive allele pedigree, both sexes are affected. TRUE Recessive allele Dominant Affected have parents that are Parents are affected unaffected  heterozygotes (carriers) ½ offspring are affected when ½ offspring affected parents are unaffected Tutor: Christina Phan Week 3 Wor
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