Genes and Gene Technology
Chapter 7
What do Genes Look Like?
• 1869- DNA isolated from a cell nucleus
– Unclear of function, or role in inheritance
• 75 years later 1944-Oswald T. Avery
– Discovered DNA is the carrier of genetic information
• Each strand of DNA contains 9 billion base pairs
• If you could print a book with genetic information of one cell it would be
500,000 pages long
• Uncoiled DNA about 2m long
Pieces of a puzzle
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Traits are determined by genes
Genes are passed from one generation to another
Genes are located on chromosomes
DNA is short for deoxyribonucleic acid
Genes material must carry out two functions
– Supply complex instructions for cell processes and for
building cell structures
– Must be copied each time a cell divides
• Ensures heredity information is passed to next
generation
• 1940 genes of bacteria and viruses are made of
DNA
Nucleotides- Subunits of DNA
• DNA is made of 4 subunits-called nucleotides
• Nucleotides have 3 different types of material
– A sugar
– A phosphate
– A base
• Nucleotides are identical except for the type of base present and slightly
different shape
• Four bases
– Adanine (A)
– Thymine (T)
– Guanine (G)
– Cytosine (C)
Nucleotides
• Can you imagine
how they might
fit together?
(sugar)
Chargaff’s Rules
• 1950 biochemist Erwin Chargaff
– Studied samples of DNA from different organisms
– Amount of adenine in DNA always equals the amount of thymine
– Amount of guanine in DNA always equals the amount cytosine
– Chargaff’s rules are represented as follows
• A=T
• G=C
• Ratio of units in a DNA strand differ between organisms
• http://www.dnalc.org/view/15495-Chargaff-s-ratios-3Danimation-with-narration.html
Picture of DNA
• Chemist Rosalind Franklin
– Created images of DNA molecules
– X-ray diffraction
• X-ray hits a particle within the molecule
• Ray bounces off the particle
• Pattern is captured on film
– DNA has a spiral shape
James Watson and Francis Crick
• Built models of DNA
• DNA resembles a twist ladder shape known as a double helix
• Used model to predict how DNA is copied
• Crick is said to have exclaimed
“We have discovered the secret of life”
DNA Structure
• Refer to page 154 (picture)
• DNA structure
– Two sides of the “ladder” made of alternating sugar and phosphate
molecules
– Rungs are made of a pair of nucleotides
• Adenine always pairs with thymine
• Guanine always pairs with cytosine
• (remember Chargaff’s rules)
• Bases must pair up a certain way
• If a mistake happens, the gene will not carry the correct
information
Making copies of DNA
• Remember adenine always bonds with thymine and guanine always
bonds with cytosine
• Bases on one side of the molecule become a template (pattern) for the
other side
• One side is complimentary to the other side
• Example ACCG would have the sequence TGGC on the other side to form a
new complimentary side
• Creates two identical molecules of DNA
• DNA molecules are split down the middle where the two bases meet
• Each side of the ladder is able to pair with additional nucleotides that are
free in the nucleus
See photo pg. 155
Trait to Gene
• Bases on one side of a molecule can be put in any order
• Enormous variety of genes
• Each gene has a string of bases, the order of the bases gives the cell
information about how to make each trait
• DNA functions the same way for all organisms
• Faulty or missing genes cause disease
– Cystic fibrosis
– Sickle cell anemia
– Scientists hope to be able to treat genetic disorders someday by
altering genes within body cells
– Refer to picture on page 156-157
Traits
• Mendel’s findings uncovered basic principles of how genes are passed
from generation to generation
• Incomplete dominance
– Mendel found that different traits did not blend together to produce
an in between form
– Since then researcher have found that sometimes different traits are
equally dominant
– Each allele has its own degree of influence (incomplete
dominance)
– Ex. red and white snapdragons-produce pink snapdragons
Traits
• One gene can influence many traits
– Ex. white tiger
– White fur influenced by a single gene
– This gene also influences eye color
Many genes can influence a single trait
• Several genes acting together influence
– Skin color
– Hair color
– Eye color
• Difficult to tell sometimes if a trait is the result of a dominant or recessive
trait
• You may have blue eyes, probably a different shade than the blue eyes of a
classmate
• Different alleles result in slight differences in the amount of pigment
present
Environment
• Genes aren’t the only thing that influences your development
• Consider the importance of:
– Healthy diet
– Exercise
– Examples set by adults
• Genes may determine that you can grow tall
– Must receive the proper nutrition to reach
your potential height
– Talent may be inherited but must be developed