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Genetics
The science that relates to the study
of genes and the patterns of heredity
Please don’t talk over the lesson….raise your hand if
you have a question to make.
Thank You
Heredity
A puppy gets
its traits from
its parents
just as we get
ours from our
parents, but
just how are
traits
inherited?
KARYOTYPE
Each human has 46
chromosomes
located in their body
cells nucleus of the
cell (diploid cells)
These are divided
into 23
chromosomes- a
baby inherits one
chromosome from
each parent from
each pair of
chromosomes
Of the 46 total
chromosomes,
two of them
are sex
chromosomes.
XX- female
Xy- male
A piece of DNA on a chromosome is called a gene. Genes also come
in pairs. They determine many of the characteristics of a baby.
Alleles, are variations of a
gene, and they usually
come in pairs. Alleles
determine the appearance
of our characteristics
There are at least two
alleles for every
characteristic
If the two alleles are the
same then it is said to be
homozygous for that gene
If they are different then
they are heterozygous
Gregor Mendel
 Gregor Mendel is known as
the father of genetics
 He was born in Austria in
1822
 He grew up on a farm and
learned a lot about flowers
and trees
 When he was 21 yrs old he
joined a monastery and
became a monk. As a monk
he taught science and
performed scientific
experiments
• Mendel spent most of his time and energy
performing experiments with pea plants
• He was very curious as to how offspring
inherited their traits
• He used pea plants in his experiments because
peas had many desirable traits that made
them easy to work with
GREGOR MENDEL
USED PEAS FOR HIS
EXPERIMENTs- WHY?
• Peas were a good choice because
• They grow quickly
• They come in many varieties with
easy to observe traits: round,
wrinkled, yellow, green, smooth
bumpy, tall, short
• Some cross pollinate, others selfpollinate
• Self –pollination was important
because Mendel was able to grow
true- breeding plants for his
experiments
• Mendel noticed that one trait was always
present in the first generation and the other
one seemed to disappear
• He called the trait that appeared the
dominant trait and the trait that seemed to
fade away the recessive trait
• To find out what might have happened to the
recessive trait, Mendel decided to perform
another set of experiments
P stands for the
parents of the first
generation (purple
flower crossed with
white flower)
F1 stands for the
offspring of the a self of
the purebred cross
above.
F2 stands for the
offspring when an F1
flower is self-fertilized
were crossed.
• Brown eyes is a dominant trait, so we would
write the genotype for brown eyes as BB, Bb
• Blue eyes is a recessive trait. The only way to
show a recessive trait is to have a genotype with
two recessive alleles, such as bb
Alleles
• An allele is a variation of a gene:
BB, Bb, CC, Cc, cc, DD, EE, ee
Some alleles are dominant and some alleles are
recessive. Dominant alleles are represented by
capital
letters in genetics, and recessive alleles are
represented by lower case letters
Genotype and Phenotype
• Genotype is the
combination of alleles
that code for a specific
trait
DD for example could be
the genotype for having
dimples.
• Phenotype is the
physical appearance
that the genotype
codes for.
• Dimples is a phenotype.
What is a phenotype
that you have?
PHENOTYPES
Your adorable
smile, the shape and
color of your eyes,
and your hair
texture are just a
few examples of
phenotypes
We know that genes
determine our
smile, but what
about personality?
Yes, some of our
personality is
hereditary, but part
of it is also a result
of the environment
we are exposed to
as a child
Nature vs.
Nurture
Homozygous and Heterozygous
Genotypes
• Homozygous
genotypes with either
all dominant alleles or
all recessive alleles
(think: the same)
• DD, dd, cc, CC, EE, ee,
FF, gg, GG, dd, DD
• Heterozygous
genotypes have at least
one dominant allele and
one recessive allele
• (think: different)
• Dd, Ff, Gg, Ee, Ee, Cc,
Gg, Rr...
Punnett Squares predict the possible genotypes of
offspring in a particular cross using the genotypes of the
parents
What color feathers will the offspring in
the test cross below have?
PTC tasting is a dominant trait
A brown furred rabbit (Bb) mates with a white furred
rabbit (bb). What is the probability that they will have
dark-furred offspring?
Answer:
• Approximately 50% of their offspring will be dark-furred,
with a heterozygous (Bb) genotype.
• What percent would likely have the recessive phenotype of
white fur?
• To show the recessive trait, the offspring must have
inherited two recessive alleles (bb), one from each parent.
They also have a 50% chance of having white furred
bunnies…..
Punnett Square Problem
• Two brown furred rabbits with the genotypes
Bb mate and produce ¼ offspring that are light
furred with the genotype bb. How is this
possible?
Answer
• The ¼ offspring received one recessive allele
from each parent giving them a recessive trait
• True or false
A puppy receives half its genes from its
mother and half from its father
Incomplete
Dominance
An inheritance pattern
where neither allele is
dominant, but instead
the phenotype of the
offspring is in between
both homozygous
genotypes
In this case, the R allele
codes for a red color, so
the more of this of this
protein, the more red
the petal color
Codominance
• An inheritance pattern where neither allele is
dominant, but rather they share dominance,
and thus, the offspring will have traits of both
alleles if it inherits one of each
Human blood type is determined
by codominance
There are three alleles for blood
type. We inherit two from our
parents.
IA and IB share dominance and i is
recessive
See chart to the side….
A person with alleles A and B is
neither A or B blood type, but
rather, blood type AB.
A person must have two i alleles
to have blood type O because O
blood type is a recessive trait.
Type A and B
individuals can
be either
homozygous
(IA,IA, or IB, IB),
or heterozygous
(IA i, or IB i)
A person must
have two i alleles
to have blood
type O
• A woman with blood type
A and a man with type B
blood could potentially
have offspring with which
of the following blood
types?
Multiple Genes
• Some traits, such as hair, eye and skin color
are determined by multiple genes, giving a
wide variety in the colors produced
Environment
al Influences
• Some genes can remain
unexpressed until something in
the environment influences it
• For example, some people have
a gene for developing lung
cancer that may not be
expressed unless the person is
exposed to the chemicals in
tobacco
• The Himalayan rabbit has a gene
for fur color that produces dark
fur, but it is only activated at
cooler temperatures, which is
why the cooler body parts, like
ears and nose are black.
These Rabbits have a gene that causes fur color to be
black if exposed to low temperatures
EYE COLOR
• Different eye colors are produced because of
the different amounts and patterns of
pigments in the iris (colored part of the eye),
which is determined by one’s genetic make up
• The DNA inherited from one’s parents
determines what color eyes they will have
• Right now there are three known gene pairs
that control eye color, and at least two are
incompletely dominant
• The bey 2 gene on chromosome 15 has a
brown and blue allele
• On chromosome 15 the bey 1 gene contains
the central brown gene
• On chromosome pair 19, the gey gene
contains a blue allele and a green allele
BB Xbb
All children with Bb genotype
Bb X Bb
Possible genotypes: BB,Bb,Bb,
bb
Can two brown-eyed parents have a blue-eyed
child? Explain and show your work.
Yes, if both are heterozygous for brown eyes and
the child inherits a recessive allele from each
parent. There is 25% chance…
 A green allele is dominant to a blue allele
 And brown allele is dominant to both a blue and a
green allele
 For the bey 2 gene if a person has a brown allele then
they will have brown eyes
 In the gey gene the green allele is dominant to the blue
alleles but still recessive to brown
 A person will have green eyes if they have a green allele
on chromosome 19 and all or some blue alleles
 Blue eyes is produced by having only recessive genes
 So for a blue eyed person all four alleles have to be blue
• If two parents have a blue and a brown gene,
there eyes are brown, but they can have a
blue eyed child if the child inherits a blue gene
from each parent
• If the child inherits one blue gene and one
brown gene the child will have brown eyes,
because brown is dominant to blue
Heterochromia- condition where a
person has two different colored eyes
What are the causes of
heterochromia?
• Disease or injury to that affects the health of
the melanocytes (cells in the eyes that
produce eye colors)
• Wardenburg Syndrome- A mutation in certain
genes that causes melanocytes to get lost on
their way to where they are supposed to go
• Chimarism (very rare!)- when two fertilized
eggs fuse to form one egg, each with a
different set of DNA
David Bowie
Genetic Disorders
 A genetic disorder is one that is caused by abnormalities
in the genes or chromosomes
 While some diseases, such as cancer, are caused by
genetic abnormalities in some cells, a “genetic disease” is
one that is present in all cells and has been present since
conception
 When something goes wrong with the chromosomes in
processing a new human being, the code cannot be read
properly and the child’s brain and body may not develop
properly. When a problem results from this genetic
mistake, we call is a genetic disorder.
Karyotype
 A karyotype is a picture of
all the chromosomes in a
cell
 A normal human
karyotype has 46
chromosomes, 22 are
identical pairs
 The other two are the sex
chromosomes.
 Is this the karyotype of a
male or a female
individual?
Turner’s Syndrome XO
 Occurs 1 in every 2000
 These women have only
45 chromosomes; they are
missing an x chromosome
 They are genetically
female, but do not mature
sexually during puberty
and are infertile
 They have a short stature
 98% of these fetuses die
before birth
Trisomy X
• A condition where a
female has an extra
copy of an X
chromosome, typically
inherited from the
mother
• It is a random event
• Typically diagnosed
later in life, if ever
Trisomy X (XXX)
• Sometimes there are no
symptoms and symptoms
vary a lot between
individuals
• Possible symptoms:
• Tall stature
• Speech and language
delays
• Delayed motor skills
• Below average
intelligence
• Occurs 1 in 1000 births
• These women are fertile
and capable of having
normal (XX) and (XY)
children
Super Male XYY
 These are males with an
extra Y chromosome
 They tend to be taller than
average
 More prone to acne
 Usually have a low mental
IQ
 Used to be thought that
these men were more
likely to end up in prison,
but no study was able to
back this claim
Klinefelter’s Syndrome XXY
• A chromosomal condition that affects a male’s
sexual development
• Most males with this have an extra copy of the X
chromosome in each cell
• Because the testicles of these males do not form
normally, affected males may have low levels of
the hormone, testosterone, beginning during
puberty
• A lack of this hormone can cause breast
development, reduced facial and body hair, and
the inability to father children (infertility)
Klinefelter’s Syndrome
Down Syndrome
 This individual has an extra # 21
chromosome, instead of two
copies, they have three
 The extra chromosome causes
physical differences in
appearance as well as learning
challenges
 About half of these individuals
have heart defects
 These children did not used to live
very long due to heart defects and
other ailments, but today they are
able to live in to adulthood,
thanks to advances in medicine

Down Syndrome
A medical procedure
used in prenatal
diagnosis of genetic risk
factors, in which a
small amount of
amniotic fluid is
extracted from the
amnion or the amniotic
sac around the fetus,
and the fetal DNA is
examined for genetic
abnormalities
A commonly used test
to detect Down
Syndrome- has a 99%
accuracy rate
Amniocentesis
which can result in harm to the baby
if it is not performed correctly and
carefully
Chorionic Villus Sampling
• Another diagnostic test to help detect genetic
abnormalities, such as Down Syndrome
• Done early in pregnancy (around tenth week)
• 1 in 100 chance of miscarriage
• Chorionic villi are tiny finger-shaped growths
in the placenta
• The DNA in the villus projections are the same
as in the baby’s cells, so in this test, samples
of the chorionic villus cells are taken for a
biopsy for the chromosomes to be studied
Multiple Sclerosis
• This is a chronic inflammatory disease of the
immune system
• Two genes have been found to increase a
person’s risk for MS, and they are found in the
immune system
• The person’s immune system begins to attack the
fatty covering around the axon of a nerve cell,
called a myelin sheath, this interrupts the
electrical signals necessary in the relaying of
impulses from one nerve cell to another
In patients with multiple sclerosis, the axon’s myelin
sheath is destroyed by the person’s own immune system
Albinism
An albino is a person or
animal who lacks the
pigment, melanin, the
protein that gives skin,
eyes, and hair color. This
is due to a recessive
inheritance pattern.
These people are prone
to vision problems and
sun burning because of
the lack of melanin.
Albinos inherited a recessive allele one from each parent. This recessive gene causes the
individual to have no melanin production, and so their skin, hair, and eyes lack
pigmentation (color)
Sickle Cell Anemia-one bad copy of a gene for this disease and the person is
carrier, two bad copies and the person is affected with the disease
 One out of 500 African
Americans has sickle cell
anemia
 This disease is caused by a
mutation in the alleles for a
gene that carries
instructions for how the
protein hemoglobin in red
blood cells should look like
 The error causes the protein
to come out with the wrong
shape
 It causes red blood cells to
collapse and into sickle
shapes that are hard and
sticky
Sickle Cell Can Cause Clots in
Arteries and Veins
 Sickle cells do not carry
oxygen as well as normal
red blood cells and they
sometimes get stuck in
the blood vessels causing
a clot
 It can cause chronic
anemia and pain
 Anemia means the blood
is low in oxygen
 Two cures: bone marrow
transplant or hydroxyure
drug
Cystic fibrosis
 Cystic fibrosis is a fatal
genetic lung disease caused
by a defect in the CFTR gene
 This gene makes a protein
that controls the movement
of salt and water in and out
of your cells
 This gene does not work
right and results in a thick,
sticky mucus in lungs and
salty sweat
 With better treatment,
people with CF are living
longer-may live into their
30’s
A child must carry two abnormal copies of the CFTR gene,
one from each parent to have the disease. If the child has
one copy, he or she is a carrier
If the problem lies on a sex
chromosome, we call it a sex-linked
disease or disorder
• Hemophilia and Color Blindness are two sexlinked recessive disorders we will discuss in
this class. For both, the problem lies on the X
chromosome with a recessive inheritance
pattern.
Color blindness is a Sex -linked
recessive disorder
 This condition is more
common in males than in
females because the
problem lies on the X
chromosome (we’ll do
pedigree charts on this)
 Humans have three color
receptors, if one or more are
faulty or missing, a person
will not see all the colors
 Red/green colorblindness is
the most common
A color blind person could not see the numbers and
letters inside the squares
Hemophilia
• An X linked chromosomal disorder in which a
person does not clot blood well
• With hemophilia a person lacks the gene for
proper blood clotting.
Pedigree Charts show the patterns of inheritance among
families; it is a tool used by geneticists to help council
patients who are worried that they might pass down a
faulty gene to their children
Cri du Chat
• A rare genetic disorder which results from the
deletion of or loss of a significant portion of
the genetic information of the arms of the
chromosome #5
• Infants with this disorder have a distinctive
high pitched cry which sounds like a cat
• The disorder is also characterized by mental
retardation, delayed development, small head
size, distinctive facial features, low birth
weight, and weak muscle tone
Gene Therapy
 Gene therapy is a technique for correcting defective
genes responsible for disease development
 Several approaches are used:
 A normal gene can be inserted into a nonspecific
location in the genome to replace a nonfunctional
gene (using a carrier, vector, to deliver the gene)
 An abnormal gene can be repaired through
selective reverse mutation
 The regulation of a gene (degree to where it is
turned on or off) can be altered
 Gene therapy is still a new area in science and is
considered to be in experimental stages
How Does Gene Therapy work?
 In most gene therapy cases, a normal gene is inserted
into the genome to replace an abnormal gene
 A carrier molecule such as a vector is used to deliver
the therapeutic gene to the patient’s target cell
 Currently the most common vector is a virus that has
been genetically altered to carry human DNA
 Viruses have evolved a way to encapsulate and deliver
their genes in to human cells to cause disease, so
scientists have tried to take advantage of this capability
and manipulate the virus by removing disease causing
genes and replacing it with therapeutic ones.
Factors that prevent gene therapy from
being an effective way to treat genetic
diseases