molecular genetics experiment: In what way do the percentages of yellow leaves vary between dishes on Day 2? How do you account for this difference? Compare the percentage of yellow seedlings in dish 2 on day 2 with the percentage on day 4. What is the difference? What experimental variable accounts for this difference? How can you account for the difference between the seedlings in dish 1? Is the yellow color genetically or environmentally controlled? How can environmental factors affect inheritance? (Use human height as an example.)

1. dermis

2. chemical

3. urine

4. viruses

5. antibodies

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.

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