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APPLIED GENETICS
GENE-CHROMOSOME THEORY
* genes and chromosomes are made up of DNA, which is the genetic material for
all life on earth (the structure of DNA will be talked about in detail next packet)
* a gene is a segment of DNA that codes for one type of molecule
* genes are found in specific places on chromosomes called LOCI
* chromosomes are condensed coils of DNA that contains thousands of genes--so
they are responsible for THOUSANDS of molecules
Applied
Genetics
* when a change happens in the genetic code (that is DNA--that is, a gene--that is,
a chromosome), it is called a MUTATION
MUTATIONS
* a change in the genetic information (DNA)
* can happen in any cell of the body
IN BODY CELLS: normally, not too much damage because only a few cells are
generally changed
IN SEX CELLS: can affect a new organism if the gametes are involved prior to
fertilization
I. TYPES OF MUTATIONS
A) Chromosome Mutations
* because chromosomes are made of thousands of genes, these mutations can
have a very large impact on the organism
1) Chromosome Number
* normally, there are 46 chromosomes in diploid human cells; and 23
chromosomes in monoploid human gametes
* now, remember MEIOSIS?
INTERPHASE -->SYNAPSIS -->A TETRAD -->CROSSING OVER ->DISJUNCTION
see what is
meant by
nondisjunction
a
comprehensive
guide to all
things involving
genetics;
download it as a
stand alone
demo here
when the pair of homologous chromosomes separate
* when the chromosomes do not split during the process of meiosis, it is called
NONDISJUNCTION
* in this case, gametes can have more or less than the n number of chromosomes
Down Syndrome is an example of NONDISJUCTION
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varying degrees of retardation
disfigured features
occurs when you have nondisjuction of chromosome 21 (3 instead of 2); this
is also called trisomy 21
total of 47 chromosomes
* if an entire set of chromosomes fail to separate, you have a polyploid organism
(where the chromosome number is 3n or 4n instead of the diploid 2n condition
* polyploidy is common in plants, an example is the funky plump strawberries
* in animals, polyploidy is usually lethal: this is because so many genes are
affected, and animals are much more complex than plants
2) Chromosome Structure
* when pieces of chromosomes are "broken" off or have other pieces added on
* sometimes can be very harmful, but depends on the number and type of genes
that are affected
ADDITION: the gain of a portion of a homologous chromosome
DELETION: the loss of a portion of a chromosome
TRANSLOCATION: the gain of a portion of a non- homologous chromosome
these video clips
explain the
chromosome
mutations of
additions,
deletions, and
translocations
See the different
types of
chromosome
mutations, as
also see to the
right.
B) Gene Mutations
* affects many less traits than chromosome mutations do
* results from a small change in DNA
* some are not harmful--albino or dwarf
* others are not seen
* MOST are RECESSIVE and HARMFUL; are called lethal alleles
* every human is a carrier for about 5 to 7 different lethal alleles
* a beneficial mutation would be one where the organism is better suited to fit in its
environment--this is EVOLUTION
II. MUTAGENIC AGENTS
* things that cause or increase the amounts of mutations (changes) in an
organism's DNA, examples:
1) RADIATION:
* cosmic rays, X-rays, UV (ultraviolet rays, radon, radioactivity, microwave
Applied Genetics
radiation, cell phones?
a comprehensive
guide to all things
involving genetics;
download it as a
stand alone demo
here
* different amounts of radiation can cause small changes in DNA
2) CHEMICALS:
* benzene, formaldehyde, asbestos, many of the additives in tobacco products--all
known carcinogens (cancer-causing chemicals)
* different amounts of these chemicals can cause changes in DNA
III. EFFECTS OF THE ENVIRONMENT
* besides genes controlling our characteristics, the environment also plays an
important role in making organism what they are
many examples...
1) hair/skin color and sunlight
* some people's hair/skin changes colors with different amounts of sunlight
* the sunlight causes an increase in melanin production in skin
2) sunlight and chlorophyll
* plants will produce chlorophyll in sunlight, otherwise, it will only make yellow
pigment
3) temperature and the Himalayan rabbit
* when the temperature is warm, the fur is white; when the temperature is colder,
the fur is black
* this enables the rabbit to stay warm--black fur absorbs more sunlight!
4) identical twins
* are identical twins truly identical? NO!
* over time since birth, they probably have had changes in the DNA (mutations),
but not the same!
* also, their social and physical environment help shape their personalities
IV. APPLICATIONS OF GENETIC THEORY
A) Artificial Selection (breeding):
* when you choose the parents because of their desirable traits
horses --> mules
ee how dogs have * ex. dogs, apples,
been bred to the
many different
types of modern B) Inbreeding:
day dog
* "crossing" of 2 parents with very similar genetic backgrounds
* can lead to genetic defects by combination of similar lethal alleles
C) Outbreeding (hybridization):
* "crossing" of 2 parents of the same species with very different genetic
backgrounds to minimize genetic defects
V. HUMAN HEREDITY
all of the Mendelian principles that we
learned last packet hold true for humans
Applied Genetics
click on the 'Selectiv
Breeding' animation
to show how to bree
a better crop throug
natural farming
methods
a comprehensive guide to all things involving
too...however, because humans are not
genetics; download it as a stand alone demo
suitable for experimentation, some
here
knowledge is limited
A) Polygenic Inheritance
* when 2 or more genes influence a
phenotype (many-genes)
* not to be confused with multiple alleles
* many human traits are caused by
polygenic inheritance: eye color, skin color,
and height
Say that the genes A and B control human
height. The dominant allele would be for
tall and the recessive allele will be for
short. However, the total height depends
on the amount of tall genes you have.
AABB
aABB, AaBB, AAbB, AABb
AaBb, aABb, AAbb, AabB, aABb, aaBB
learn a little about oncogenes; the
genes that when mutated lead to
cancer
Aabb, aAbb, aaBb, aabB
aabb
B) Oncogenes
Applied Genetics
* genes that are responsible for abnormal
cell growth -- CANCER
* ALL CANCER IS GENETIC; IT MIGHT
NOT BE ACTIVATED YET
* certain genes can cause cancer if they
are changed--mutated
* this change can cause the cell to carry
out repeated cell divisions and ignore
signals to stop
C) Genetic Counseling
* by looking at the traits of your ancestors,
you can learn more about your genotype
and that of your offspring
* genetic counseling use techniques such
as:
1) genetic screening
* the chemical analysis of body fluids such
as blood, urine, semen
2) amniocentesis
* the removal of amniotic fluid for chemical
and/or cellular analysis...used with
3) karyotyping
* the preparation of an enlarged
photograph of paired homologous
chromosomes
* can see chromosomal (gene)
abnormalities like chromosome mutations,
nondisjunction (Down's Syndrome), and
polypolid sets
VI. GENETIC DISORDERS IN HUMANS
a comprehensive
guide to all things
involving genetics
download it as a
stand alone demo
here
A) PKU (Phenylketonuria)
* caused by a recessive allele (need 2 copies to express it)
* development of mental retardation
* occurs when one gene does not produce the enzyme (a protein) needed to break
down phenylalanine (an amino acid)
* can "treat" with a diet low in phenylalanine
B) Tay-Sachs
* caused by a recessive lethal (fatal) allele
* nervous system shuts down at an early age; usually before 6-8 years
* fatty material accumulates in the nervous system because of an enzyme cannot
be produced
* found most often in European Jewish heritage and Pennsylvania Dutch (Amish)
C) Cystic Fibrosis
* caused by a recessive allele on chromosome 7
* glands produce a thick mucus that clogs and damages the lungs
* found most often in Caucasians
D) Huntington's Disease
* caused by a DOMINANT ALLELE; those that have this allele will develop this
genetic disease
* this disease causes a progressive breakdown of the brain cells followed by death
* however, symptoms do not develop until after the person is over 30-35+ years old
E) Sickle-Cell Anemia
* caused by a recessive allele but follows incomplete dominance; two copies-severe cases, one copy--moderate case
* the allele changes the structure of hemoglobin; under certain conditions, the
abnormal hemoglobin cause the biconcave shape of the red blood cells to change
PI: Pedigree
nvestigator, On the * blood vessels can become blocked (painful) and red blood cells do not carry
Case of Nicotine enough oxygen (anemia)
Addiction, from the * common in people of African decent
Genetic Science
Learning Center
VII. PEDIGREES
* a way to track genes through a family
* symbols usually are the same
- circles are females
- half-filled circle means a female carrier
- filled circle means female with condition
- squares are males
- half-filled squares means a male carrier
- filled square means male with condition
- shape with a line through it means deceased
* sometimes these can get pretty complex
Try this pedigree out. Draw the 'symbols' for each person, then answer the
questions at the end. This family treeinvolves two families and tongue rolling:
(R=DOMINANT, a roller; r=recessive, non-roller)
Place the persons genotype in their respective shapes (RR=homozyogus
dominant, Rr= heterozygous, R_=if the person is a tongue roller but you do not
know if they are homozygous or heterozygous, and rr=a non tongue roller)
Narly Story
Fred Narly, a tongue roller, broke with family tradition and married a non-tongue
rolling person, Joan Fool in 1944. Fred and Joan proceeded to have two children:
Fred Jr. and Mary. Fred Jr. carried on the Narly tradition of tongue rolling while
Mary was often chastised and berated for her inability to roll her tongue.
Fred Jr. married a tongue rolling woman named Jean Gueeba, while Mary tried to
redeem herself and marry a tongue rolling man named Steve Dorhoff.
Fred Jr. and Jean had two children: Nancy and Frank. Nancy was a true tongue
rolling Narly. While Frank was almost disinherited from his dad's will because he
could not roll his tongue.
Mary and Steve Dorhoff had a daughter, Sarah. Unfortunately, Sarah couldn't roll
her tongue.
Frank eventually ran away from home because he didn't want to bring shame to the
family. Nancy Narly settled down with Bill Quiff. After the wedding, the Narly's
discovered that Bill could not roll his tongue.
Sarah Dorhoff married a man named Ted Goof. Ted was accepted into the family
due to the fact that he could roll his tongue. Unfortunately, Ted died when he
choked on a bad Chalupa. After Ted's death, Sarah never remarried and did charity
work to help non-tongue rollers. But before Ted's death, Sarah became pregnant
and eventually had Craig Goof. Much to everyone's relief, Craig could roll his
tongue.
Meanwhile, Bill and Nancy Quiff also had a child named Candice Quiff. Again,
everyone was relieved when Candice could roll her tongue.
At a party in college, Candice Quiff and Craig Goof met and fell in love.
Dorhoff Story
In 1945, Neil Dorhoff and Marie Shoo, both tongue rollers, had a whirlwind affair
and married. They had three children, Steve, Maureen, and Tom. Steve was
always the favorite son because he could roll his tongue, while Maureen and Tom
could not. Unfortunately, Tom died in a bizarre gardening accident.
Steve Dorhoff married Mary Narly and had a child named Sarah.
Maureen met and married Bob Lee, a person who took his tongue rolling seriously.
Bob and Maureen had a child named Clarence. Luckily for the Lee's, Clarence
could roll his tongue.
Questions:
1) What type of 'relative are Candice and Craig? Can they marry legally in the US?
Should they?
2) If Candice and Craig did have a child, what is the possibility that the child could
roll his/her tongue? Show the Punnett square.
3) If Clarence marries a lady named Lucy Lavender who was not a tongue roller,
what is the possibility that their child could roll his/her tongue? Show the Punnett
square.