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David Hein
DNA Investigation 3
Biology, Miller
6 December 2010
I have blue eyes. The rest of my family though has brown eyes. I am always wondering
why I have blue eyes, yet every one in my family has brown. Well, the answer to this is DNA.
DNA shapes how everything and everyone looks. From your eye color to your hair, your DNA
affect everything. The important genetic factors that affect how you look are: DNA, genes,
chromosomes, RNA, proteins, gene expression and inheritance.
DNA is a major part of how you look. DNA stands for deoxyribonucleic acid. Most
DNA is found in the nucleus of a cell (nuclear DNA). The function of nuclear DNA is to store
and transmit genetic information. This tells cells what proteins to make. There are four
nitrogen-containing bases found in DNA. They are A- Adenine, G -Guanine, C-Cytosine, and TThymine. Adenine combines with Thymine and Guanine combines with Cytosine. These are
called complementary base pairs. Adenine and Guanine are purines and Thymine and Cytosine
are pyrimidines. The pyrimidines and purines are bonded together with hydrogen bonds. The
pairs are held on with deoxyribose and phosphate molecules in a sequence that curves to make a
double helix.
Replication of DNA is important to create identical new cells. The first step is the
unwinding of the chain by an enzyme called helicase. This breaks the hydrogen bonds apart and
the two paired strands of nucleotides are now separate. Then the other half of the DNA is copied
by DNA- polymerase and creates their nucleotide partner. Nucleotides are joined to new
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covalent bonds and phosphate groups and bonded to the old nucleotides by hydrogen bonds.
There are now two helixes of DNA.
DNA Helix
Genes are play a major role in who you are. Each person has two copies of each gene.
Genes are segments of DNA that contain the coding for making polypeptides or protein. The
Human Genome project estimates that humans have between 20,000 and 25,000 genes. Some
genes are called housekeeping genes. They enable the cells to make the proteins needed for
basic functions. Other genes are inactive most of the time. An example of this are genes that are
active only during early embryonic development and then become inactive. A third type of gene
encodes proteins unique to each kind of cell character such as a brain cell. Cells activate genes
when needed and suppress them when not needed.
Chromosomes play a major role in your heredity. Human cells have two sets of
chromosomes. One set from the mother and one set from the father. Each human cell contains
23 pairs of chromosomes. These include twenty-two pairs of autosomes and 2 pairs of sex
chromosomes. Females have two X chromosomes and males have one X and one Y
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chromosome. A karyotype that show the numbered chromosomes is done in genetic testing to
show the sex of the baby and to show other genetic factors.
Chromosomes are long strands of genes found in the cell nucleus. Chromosomes are two
very longs thin strands of thickly packed DNA chains. These chains become more thickly
packed during cell division. Each chromosome looks like an X. The constriction point of this X
is called the centromere. The centromere makes sure the chromosomes are correctly distributed
to the new cells. The top, short parts of the X are the”p” arms and the long, bottom parts of the
X are the “q” arms. These arms make up the part of the chromosome called the telomere.
Telomeres stop the chromosome from shortening during replication.
Karyotype
RNA play a major role in making proteins that shape who you are. RNA (Ribonucleic
acid) is made up of nucleotides much like DNA. The difference between RNA and DNA is that
RNA is made up of ribonucleic acid instead of deoxyribonucleic acid. The nucleotides are also
slightly different. Uracil replaces Thymine in RNA and is paired with Adenine. There are three
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basic types of RNA which are; mRNA, tRNA, and rRNA. mRNA is the messenger of genetic
information. It carries the information from the DNA is the nucleus to the cytosol. tRNA is
transfer RNA. It is about 80 RNA nucleotides. It folds into a hairpin shape and binds to an
amino acid to deliver to the ribosome. rRNA combines amino acids to form proteins.
Transcription is the process where RNA is made from DNA. The enzyme RNA
polymerase binds to the DNA. There are three stages of transcription. The first is initiation
where the RNA polymerase binds to the DNA at a specific sequence of nucleotides called the
promoter. The RNA polymerase then unwinds the DNA at the start of the gene. The second step
is elongation. One of the unwound DNA strands is a template for the RNA. RNA polymerase
forms the mRNA. The transcribed DNA re-winds to the double helix. The third step is
termination. The new mRNa is released.
The flow from DNA to RNA to protein synthesis is basic to molecular biology. This is
sometimes called the “central dogma”. The purpose of protein synthesis is to create a
polypeptide, which is a protein made out of a chain of amino acids. Proteins are used inside
cells, sent out of cells or excreted from cells. An example of protein made in the body is hair or
keratin. The protein is made into long fibers. These protein fibers emerge from your scalp.
Collagen is a protein that is part of you skin, muscle and bone. Hemoglobin is a protein that
carries oxygen in red blood cells.
Gene inheritance and expression plays a major role in your appearance. It shows through
your health, personality and character traits. In gene regulation signals from the environment
from other cells activate proteins called transcription factors. After the gene is read and copied it
is then translated to build a protein. These regulation signals can change as the environment
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changes and therefore your body might adjust with the environmental changes. A particular
medical condition may be in your genetic make-up and certain conditions may switch this
condition on or off.
The founder of genetics is Gregor Johann Mendel. He was an Austrian monk who
worked with garden peas and observed different traits in the plants. Mendel's Principles of
inheritance are as follows. The Law of Segregation: Each of the two inherited alleles possessed
by the parent will segregate and pass into separate gametes (eggs or sperm) during meiosis. Each
of these carry only one of the alleles. The Law of Independent Assortment: In the gametes,
alleles on one gene separate independently of those of the other gene. This makes all possible
combinations of alleles equally probable. The Law of Dominance: Each trait is determined by
two alleles, inherited on from each parent. These alleles exhibit a characteristic dominant, dodominant, or recessive expression. Those that are dominant will hide the expression of those that
are recessive. Reginald Punnett devised a way to determine the probability of offspring having a
particular trait. It is the summary of every combination of one maternal allele and one paternal
allele for each gene.
Punnett square
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The important genetic factors that affect how you look are: DNA, genes, chromosomes,
RNA, proteins, gene expression and inheritance. The reason why I have blue eyes is because a
gene encoded by my DNA tells my eye to make proteins that have blue pigment. The reason
why my family has brown eyes is because the blue eye trait is recessive. Both my parents have
the the blue recessive gene. They both have the brown dominant gene. I inherited the blue
recessive gene from both of them. This is necessary to have blue eyes. DNA is the secret code
to all life. Scientists are continuing to unravel this code to further our understanding of life.
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Works Cited
The Centre for Genetics Education. The Australasian Genetics Recorce Book. 2007: Centre for Genetics
Education, 2007. N. pag. PDF file.
"How the Body Works." About Kid's Health. The Hospital for Sick Children Genetics, n.d. Web. 7 Dec.
2010. <http://www.aboutkidshealth.ca/howthebodyworks/Gene-Expression.>.
National Center For Biotechnology Information. "What Is a Genome." National Center for Biotechnology
Information. National Center For Biotechnology Information, 31 Mar. 2004. Web. 4 Dec. 2010.
<http://www.ncbi.nlm.nih.gov/About/primer/genetics_genome.html>.
Oracle Thinkquest Education Foundation. "Dominant Vs. Recessive Traits." Oracle Think Quest. Oracle
Thinkquest Education FOundation, n.d. Web. 4 Dec. 2010. <http://library.thinkquest.org/
C0118084/Gene/Genetic_variation/dominant_recessive.h>.