It is important to know that gene expression can be influenced by environmental factors. For example, available nutrients, salinity, and temperature can influence gene expression in organisms. In E. coli bacteria, the lac operon gene is only turned on when the bacteria are using lactose as a primary food source.
Another example of environmental factors influencing gene expression is metamorphosis . Metamorphosis is regulated by external and internal factors, including temperature, available resources, and hormones. For example, a tadpole in a pond will go through many physical changes as it responds to the environment. Environmental conditions trigger hormone release that allows the tadpole to create new specialized cells so that it can survive in its environment.
Look at the pictures below. The tadpole in Figure A will spend about 16 weeks of its life undergoing metamorphosis before becoming an adult frog.
The cells of the tadpole in Figure B, living in an area of drought with less water, will release hormones to speed up the process of metamorphosis in response to its environment. Both tadpoles will survive to become adult frogs, but their cell differentiation is being controlled at different rates.
Explain how an environmental factor, like temperature, can influence gene expression. Environmental temperatures can trigger a hormone to be released that allows organisms to create new specialized cells so that it can survive in temperature.
1 . The genetic code by which DNA stores the genetic information consists of nucleotides that include three parts: a sugar, a phosphate, and a nitrogenous base. The functional segments of DNA which code for genetic information are called genes. With four possible bases, the three nucleotides can give 4 3 = 64 different possibilities, and these combinations are used to specify the 20 different amino acids used by living organisms.
2. For almost all organisms, including humans, flies, yeast, and bacteria, the same codons are used to code for the same amino acids.
Therefore, the genetic code is said to be universal. The universality of the genetic code strongly implies a common evolutionary origin to all organisms, even those in which the small differences have evolved.
1. What are the components that make up the genetic code? nucleotides that include three parts: a sugar, a phosphate, and a nitrogenous base
2. How does DNA carry information about the traits of an organism? genes
3. Why is the genetic code common to all organisms?
For almost all organisms the same codons are used to code for the same amino acids
4. What role does a common genetic code play in evolution?
The universality of the genetic code strongly implies a common evolutionary origin to all organisms

In this activity, you will be given two sequences of DNA. Sequence 1 is from a human and sequence 2 is from a cow. In both humans and cows, this sequence is part of a set of genetic instructions for controlling a bodily function.
1. Using the DNA sequence, make a complimentary mRNA strand for both the human and the cow. Write the mRNA strand directly below the DNA strand.
2. Use the codon chart to determine what amino acids are assembled to make the insulin protein in both the cow and the human. Write your amino acid chain.
Sequence 1 - Human
DNA: CCA TAG CAC GTT ACA ACG TGA AGG TAA mRNA: GGU AUC GUG CAA UGU UGC ACU UCC AUU
Amino Acids: gly-iso-val-glu-cys-cys-thr-ser-iso
Sequence 2 - Cow
DNA: CCG TAG CAT GTT ACA ACG TGG AGG C TAT mRNA: GGC AUC GUA CAA UGU UGC ACC UCC AUA
Amino Acids: gly-iso-val-glu-cys-cys-thr-ser-iso
1. Comparing the human gene to the cow gene, how many of the codons are exactly the same? 5 out of 9
2. How many of the amino acids in the sequence are exactly the same? 9 out of 9
3. Could two humans (or two cows) have some differences in their
DNA sequences for insulin, yet still make the exact same insulin proteins? Explain. Yes, the different codons that are transcribed from the DNA sequence can code for the same proteins