Download It*s All in the genes - North Buncombe High School

IT’S ALL IN THE GENES
WHY IS GENETICS IMPORTANT?
• The modern science of genetics influences many aspects of daily life, from
the food we eat to how we identify criminals or treat diseases.
Understanding genetics is particularly relevant to many current issues such
as:
• Cloning
• Stem cell and gene therapy
• Genetic testing for human diseases
• Recent privacy laws requiring personal medical information
• So……what is GENETICS?
• Humans have always wondered how traits, such as eye and hair color are
passed along from one generation to the next. The basic units of heredity
are known as Genes. The study of the function and behavior of genes is
called Genetics.
• In 1865, an Austrian monk named Gregor Mendel first studied inheritance
patterns in a scientific way. He used the garden pea plants to determine
that traits were inherited as separate units. His research formed the
foundation for later scientific achievements in the field of genetics.
JEANS OR GENES?
• Every living organism, from the smallest bacteria to the largest animal carries
a set of genes inside its cell.
• Genes are bits of biochemical information.
• DNA( deoxyribonucleic acid) is a coiled molecule that transmits the
information . It usually exists in a double-stranded form that naturally winds
together to form a double helix. The genes exist in segments along the length
of the DNA molecule.
• Chromosomes are very long, continuous pieces of DNA which contains
many genes .
• Although all humans share the same set of genes, individuals can inherit
different forms of a given gene from their parents, making each person
genetically unique…..except for identical twins. The inheritance process is
• Responsible for the variation in traits we see in nature like the color of a
flower and human behavioral traits such as musical talent.
MENDEL’S RULES: A PATTERN OF
INHERITANCE
• Mendel started his scientific study of on heritance by focusing on seven
different traits in the pea plant. One he could readily identify was seed color.
He found that :
• each trait had 2 forms: seeds were either green or yellow
• The colors didn’t blend, like if you mixed yellow and green paint
• That when he crossed a plant with green seeds with a plant with yellow
seeds, the offspring all had yellow seeds and the green color disappeared.
From this, he concluded that the gene for yellow seeds was dominant over
its alternate gene for green seeds, which were recessive. This is known as an
Allele: any one of a number of viable DNA codings of the same gene
occupying a given position on a chromosome.
R
• Genotype= the combination of genes that code for a trait
• Phenotype= describes the physical manifestation of that trait
• In an organism like Mendel’s pea plant, 2 copies exist of each of its
chromosomes so 2 alleles make up its genotype.
• Mendel’s plants had 2 alleles for the gene that controlled seed color. Yellow
being dominant and green being recessive. When he crossed these offspring
with each other, about 25% had green seeds,75% had yellow.
• Sex cells have only one set of chromosomes. When the egg and sperm fuse,
the result is a baby with half of its chromosomes from one parent and half
form the other.
EXCEPTION TO THE RULE
• Since 1865, scientists have learned that sometimes genes do not easily
conform to Mendel’s patterns of inheritance.
• Incomplete dominance: the inheritance of a dominant and recessive allele
results in a blending of traits. For example, 4o’clock plants may have red,
white or pink flowers.
• Quantitative inheritance: Mendel focused in traits determined by a single
pair of genes resulting in a phenotype that was easy to distinguish. A tall
plant is different from a short one, for example. But, some traits are not easy
to distinguish like human skin color. This trait is determined by more than one
pair of genes. At least 4 pairs of genes determine skin color.
• Multiple alleles: Certain traits are controlled by multiple alleles that have
complex rules of dominance. The gene for human blood type has 3 alleles.
• Gene linkage: Mendel studied traits in pea plants where one trait did not
appear to influence another such as the plant’s height and texture. These 2
phenotypes occur randomly with respect to one another in a manner known
as independent assortment. Today, scientists know that independent
assortment occurs when genes affecting the phenotypes are found on
different chromosomes. When genes appear near one another on the same
chromosome, they are inherited as a single unit and are considered linked.
• Sex-linked traits: Most chromosome pairs consist of identical partners. There is
one pair of chromosomes that are different, these are called the sex
chromosomes because they determine the differences between male and
female.
BREAKING IT DOWN
• DNA carries all the information our cells need to function and carries hereditary
information in a from that can be copied and passed from generation to
generation.
• The genetic code is the biochemical instruction that is found within the gene and
specifies the chemical structure of a particular protein.
• Proteins are composed of long chains of amino acids and the specific sequence of
these amino acids dictates the function of each protein.
• DNA molecules form chains of building blocks called nucleotides. They consist of a
sugar molecule called deoxyribose; a phosphate group and one of four bases:
adenine (A), cytosine (C), guanine (G), and thymine (T).
• These are the elements that make up the DNA chain. In the cells of most organisms,
2 long strands of DNA join in a single molecule resembling a spiral ladder, commonly
called a double helix. The bases of one strand join bases from another to form the
rungs of the ladder, the pairing of bases.
• The pairing of bases in the DNA double helix is highly specific—adenine
always joins with thymine, guanine always links to cytosine. These base
combinations play a fundamental role in the DNA’s function by aiding in the
replication and storage of genetic information.
• Genes line up in a row along the length of a DNA molecule. A single gene
can vary in length from 100 to more that 1,000,000 bases. Genes make up
less than 2% of the length of a DNA molecule. The rest is made up of long,
highly repetitive nucleotide sequences.
• Scientists now believe these nucleotide sequences may play a role in the
survival of cells, and identifying these function is a thriving field of genetics
research.
READING THE CODE
• New DNA is produced during mitosis=one nonsex cell splits into two; there
are only two possible base pairings- A with T and G with C. This process is
called DNA replication. During replication, the DNA strand unwinds and the
chemical bonds joining the base pairs break, separating the DNA molecule
into tow separate strands. Each strand directs the synthesis of another
complimentary strand.
• Transcription is the process the DNA goes through to produce the proteins
involved in every activity of the cell thereby producing an intermediary
molecule called ribonucleic acid (RNA). Transcription involves the
production of a special kind of RNA known as messenger RNA (mRNA). The
mRNA consists of linked exons that together make up the genetic code for a
protein.
• Translation is the process that translates the information coded in the four
bases found in mRNA into instructions encoded by the 20 amino acids used
in the formation of proteins.
• Translation takes place in cellular organelles called ribosomes. They act like a
clamp on workbench, holding the mRNA strand and coordinating the
activity of enzymes and other molecules essential to translation.
• Transfer RNA (tRNA) is responsible for reading the genetic code and carrying
the correct amino acid that the code specifies. This process continues
repeatedly, with the new tRNA receiving the growing chain of amino acids,
known as the polypeptide chain, from a resident tRNA. The process ends
when the entire sequence of mRNA has been translated. The polypeptide
chain falls away from the ribosomes as a newly formed protein, ready to go
to work in in the cell.
BEYOND MENDEL ------MOLECULAR
GENETICS
• Genetic engineering-----the alteration of genes in an organism . These tools
are used in industry to develop commercial products such as hardier crops,
microbes the can break down oil slicks, decompose garbage an improve
medicine.
• Recombinant DNA—DNA molecules are universal, all forms have the same
DNA structure and the same four bases. Scientists have made use of these
similarities in a technology called recombinant DNA. With this, scientists can
create changes in the genetic makeup of an organism that would be
unlikely to occur through natural processes.
THE FUTURE OF GENETICS
• Gene therapy: the insertion of one or more genes into an individual to treat
disease, especially inherited(genetic) diseases. In experiments using gene
therapy, researchers have replaced defective genes with normal alleles. A
gene must be delivered to the cell using a carrier or “vector”. The vectors
most commonly used in gene therapy are viruses.
•
In some gene therapy clinical trials, cell fro the patients blood or bone
marrow are removed and grown in a lab. This type of gene therapy is called
ex vivo.
• The earliest success in human gene therapy involved treatment if infants who
cannot produce an enzyme important to normal function of the immune
system. These children have a devastating disease called severe
immunodeficiency disorder(SCID), dubbed the bubble boy disease.
GENES AND SOCIETY
• If scientists have developed genetic tests that shed light on a person’s personality ,
what dilemma’s could that present?
• Eugenics is the study of hereditary improvement of the human race by controlled
selective breeding.
• Few areas of science hold as much promise or controversy as the area focused on
what happens in our bodies at the molecular level. In the coming years we can
expect much public debate about issues such as stem cell research and cloning.
DNA fingerprinting and the right of privacy, prenatal genetic testing and the ethics
of pregnancy termination and much more. Understanding basic genetics will
provide you with the tools you need to make informed decisions about these
important issues.