“It’s in Their Genes” Reading Prompt”- 2012
Name: ______________________________________ Block:________ Date:____________
What is DNA? DNA , or Deoxyribonucleic Acid, is in every living thing. DNA is made of nucleotides.
Nucleotides are made of phosphate, sugar, and base molecules. DNA bases are adenine, thymine, guanine,
and cytosine and are usually listed as A, T, G, and C. The A and T, and the C and G, fit together like puzzle
pieces to form a twisted ladder that like a “spiral staircase”.
A. What are the 4 DNA bases? _______________________________________________________________
B. Which bases pair with each other?_______ to _________; ________ to ___________
Who discovered DNA? The discovery of DNA happened in 3 main stages.
1. Chargaff finds that the amounts adenine equals thymine, and the amounts of cytiosine equals guanine.
2. Franklin makes an x-ray of DNA suggesting that it is spiral. (She doesn’t get full credit for it, though.)
3. Watson and Crick made and published a model of DNA showing the spiral staircase structure with the
A to T and C to G basepairs. They get the Nobel Prize for it. Franklin is not credited.
C. What shape does DNA have?____________________________________
D. What scientist(s) First theorized that shape?__________________________________________________
What does DNA look like in the cell? In Prokaryotic cells like bacteria, DNA is loose in the cell in a stringy or
circular form. In bacteria, the chromosomes copy, then the cell simply splits by binary fission. In Eukaryotic
Cells, DNA is usually hidden inside the nucleus unless Mitosis is occurring in the form of Chromatin. During
Mitosis, DNA thickens into chromosomes which look like little “X”s under a light microscope. Mitosis is the
small part of the cell life cycle where the nucleus of the mother cell gets copied and split into 2 new daughter
cells with identical DNA. The cell life cycle and binary fission are types of asexual reproduction which help
organisms grow or replace old cells.
E. What is the difference between mitosis and binary fission?_____________________________________
_________________________________________________________________________________________________
_________________________________________________________________________________________________
What does DNA do? DNA acts much like “boss” of a factory because it controls all of the functions of the cell,
including reproduction and protein-making. It acts like an assembly or operating manual for a toy or
electronic device. A combination of 3 nucleotides called a codon makes one part of the protein. The parts are
linked together to make a protein like connecting beads on a necklace. Each gene does this by making very
specific proteins in very specific quantities. In turn, these proteins make everything else that the cell needs.
DNA controls heredity, the passing of characteristics from one generation to the next. In asexual reproduction,
DNA is just copied. Each new cell gets an almost identical copy.
F. What does DNA do for the cell?______________________________________________________________
_________________________________________________________________________________________
G. How many nucleotides makes a codon?_________________________
How does DNA control heredity? In sexual reproduction, the DNA is split up the middle. Each egg or sperm
cell only gets half of the DNA at the end of meiosis. Meiosis is different than mitosis. At the end of mitosis you
have 2 identical cells with the same numbers of pairs of chromosomes. In humans, that would be 23 pairs for
a total of 46 chromosomes. The result of meiosis is 4 egg or sperm cells with half the number of slightly
different chromosomes. In humans, that would be 23 chromosomes. When the sperm cell fertilizes the egg
cell, the male and female halves (alleles) of the DNA combine to form an entirely new combination of the
organism. The offspring might be similar to the parents, but it has slightly different appearance and abilities,
called traits.
H. What is the result of mitosis? _____________________________________________________________
________________________________________________________________________________________
I. What is the result of meiosis? ______________________________________________________________
________________________________________________________________________________________
Why is there a difference between parents and their offspring? Those differences come from 2 things that
happen in meiosis. First, each meiosis cycle produces 4 eggs from the mother or 4 sperm from the father.
That makes 16 possible difference combinations. Second, when the chromosome pairs duplicate (double),
they are so close together that parts of them stick together. When they separate again, the parts stay with the
chromosome they to which they stuck. That process is called crossover and is a lot like shuffling genetic cards.
Amazingly, each chromosome is usually complete! Crossover is also the reason that identical or maternal
twins have minor differences between them, like different fingerprints.
J. What 2 things make offspring different than their parents? _______________________________________
__________________________________________________________________________________________
What happens when things go wrong? Damage or a mistake to the DNA molecule is called a mutation.
Mutations can come from environmental damage such as ultraviolet rays, radiation, viruses, or toxic chemicals
which cause tears in the DNA. Most tears are repaired by the DNA. But if those tears aren’t repaired, the
correct proteins aren’t made for the cell to function properly. The cell could die or malfunction causing the
organism to get sick or die. Insertion mutations happen when an extra base pair is put in the DNA sequence.
Deletion mutations happen when a base pair is removed from the DNA sequence. Substitution mutations
happen when a base pair is replaced by another in the DNA sequence such as in sickle cell anemia.
Polychromy is a mutation where an entire extra chromosome is added to a cell such as in Down’s Syndrome.
K. What is a mutation?______________________________________________________________________
L. What things can cause a mutation?__________________________________________________________
_________________________________________________________________________________________
M. What can happen to an organism if a mutation is not repaired by the DNA? _________________________
_________________________________________________________________________________________
N. What are 4 types of DNA mutations? ____________________________, ___________________________,
_________________________________________, & ____________________________________________
How do humans alter an organism’s genome? A genome is basically a listing of all the genes in all of the
chromosomes in an organism. The human genome contains over 33,000 genes in every cell. Those genomes
have developed by natural selection where characteristics that helped an organism better survive were
inherited by offspring. Unsuccessful characteristics eventually leave the genome, since those adults are less
likely to survive. Man has been altering organisms’ genomes for thousands of years by artificial selection or
selective breeding. In artificial selection, humans take 2 individuals of very similar organisms and breed them
for desired characteristics. Tomatoes are no longer poisonous and we have over 200 breeds of dogs because
of selective breeding. These are all at the organism level of cellular organization.
Since 1974, man has been able to genetically engineer the genome of some organisms at the cellular
level of organization to make Genetically Modified Organisms (GMOs). Scientists started with bacterial DNA
because it is very simple and easier to cut and splice (“glue”). They used it to make new organisms that could
make special substances, especially drugs like insulin, which diabetics need to inject to live, or bacteria to help
digest oil spills and sewage to make water cleaner. Next scientists modified plants to make them resist disease
or severe weather, or make more food per acre. This is different than selective breeding because you are
making entirely new plants directly from DNA, not from crossbreeding the actual plants.
Animals have also been cloned where actual eggs are altered with the DNA of an adult to make an
exact copy of that adult. Dolly, the sheep, was the first mammal to be cloned. Cloning doesn’t reduce the
amount of time from “birth” to adulthood. It’s done to create exact copies of an organism with prized traits.
Unfortunately these clones don’t live as long because their DNA is old. Many scientists and consumers
disagree with cloning and GMO’s because they might be dangerous or unethical. Some agree with cloning.
O. What is the difference between a GMO and a selectively bred organism?____________________________
__________________________________________________________________________________________
P. Why do scientists want to produce GMO’s or clones?_____________________________________________
__________________________________________________________________________________________