Download Ch. 4: Modern Genetics

Ch. 5: Modern Genetics
Sect. 1: Human Inheritance
Sect. 2: Human Genetic Disorders
Sect. 3: Advances in Genetics
Sect. 1: Human Inheritance
Traits are inherited through 3 inheritance
patterns.
1. Single gene with 2 alleles
2. Single gene with multiple alleles
3. Multiple genes working together
1. Single genes with 2 alleles.
– Dominant vs. Recessive.
Examples: Widow’s Peak, Sickle Cell Anemia,
Huntington’s Disease.
2. Single genes with multiple alleles.
– Multiple alleles are 3 or more forms of a genes that
code for a specific trait.
Example: Blood types: A, B, & O
A & B are codominant, O is recessive.
Blood type gene found on Chromosome 9
3. Multiple genes that work together to produce a
trait also known as polygenic genes.
– Skin color
Controlled by 6 genes; 3 received from each parent.
– Height
Total number that control height unknown
Current thinking is that there is at least 8; 4 from each parent.
– Body Built
Sex chromosomes
–
–
–
Chromosomes that carry genes that determine the
sex of a newborn as well as other genes.
The 23rd pair of chromosomes.
Female sex chromosomes (XX):
X-received from mom, X-received from dad.
Egg cell contains only X chromosomes.
–
Male sex chromosomes (XY):
X-received from mom, Y-received from dad.
X chromosome substantially bigger than Y chromosome.
Gene located on Y, called the SRY gene initiates the
release of testosterone during embryonic development to
turn embryo into a male.
Sperm cell contains either an X or a Y chromosome.
Sex-linked genes
– Genes carried on the X or Y chromosomes.
– Unlike the other 22 pairs of chromosomes, X
& Y chromosomes do not have all the same
genes.
– Sex-linked traits
Traits that are controlled by genes found on either
the X or the Y chromosome.
– Example: Colorblindness: inability to distinguish between
certain colors.
Red-Green colorblindness
Blue-Yellow colorblindness
Achromatopsia (Total colorblindness): inability to see
any colors.
– Example: Facial Hair
Gene for facial hair is found on the X chromosome &
is recessive.
– Example: Hemophilia
Genetic disorder in which the blood clots slowly or
does not clot properly resulting in excessive bleeding
when injured.
Gene for hemophilia is found on the X chromosome
& is recessive.
– Example: Male-patterned baldness
Gene for hair loss is found on the X chromosome &
is dominant.
– Example: Retinitis pigmentosa
Genetic disorder in which a person gradually loses
their eyesight eventually becoming blind.
Gene found on the X chromosome & is a dominant
gene.
– Example: Muscular Dystrophy
Genetic disorder in which a person gradually lose
muscle control throughout the body.
– Because females have 2 X chromosomes
typically they are only carriers for sex-linked
genetic disorders.
Carrier: A person who has both a dominant &
recessive allele for a trait & does not express the
trait.
– Because males only have 1 X chromosome if
the trait is located on their 1 X, they have the
trait. If it is not located on their 1 X, they don’t
have the trait.
Example:
– H: non-hemophilia, h: hemophilia
– XHXh (female with hemophilia but a carrier)
– XhY (male with hemophilia)
Environmental factors can also influence
the expression of traits.
– Lack of exercise.
– Proper diet.
Intake of proper amounts of proteins.
Intake of proper amounts of minerals.
Intake of proper amounts of vitamins.
Sect. 2: Human Genetic Disorders
Genetic Disorders
– A genetic disorder is an abnormal condition
that a person inherits through genes &
chromosomes.
– Causes of genetic disorders
1.
Mutations in the DNA of genes
–
2.
Substitution, deletion, or addition of nitrogen base pairs
in the genetic code.
Changes in the overall structure or number of
chromosomes.
–
Caused by the failure of chromosomes to separate
properly during meiosis.
Examples of Genetic Disorders
1. Cystic Fibrosis is a genetic disorder in which
thick mucus is produced within the lungs &
intestines.
Caused by the deletion of 3 nitrogen base pairs from
the DNA molecule.
2. Sickle-Cell Anemia is a genetic disorder in
which the red blood cells form a sickle cell
shape instead of the usual round shape.
Caused by the substitution of 1 nitrogen base pair in
the DNA molecule that cause the hemoglobin protein
to form incorrectly.
3. Down Syndrome is a genetic disorder in
which a person has 3 copies of chromosome
21.
Caused by the failure of chromosome 21 to
separate during Meiosis.
Typically the mother’s chromosome-21.
Also called Trisomy-21
4. Albinism is a genetic disorder in which a
person does not produce substantial
amounts of pigment within their skin, eyes,
or hair.
Albinism results from inheritance of a recessive
gene and is known to affect all organims including
humans.
Hemophilia: disorder in which a person’s body
does not clot properly due to the lack of the
production of a specific protein.
Caused because of a recessive gene found on the X
chromosome.
Hemophilia is more common in males than females.
There are 2 primary types….
Hemophilia A occurs in about 1 in 5,000 – 10,000 male
births.
Hemophilia B occurs in about 1 in 20,000 – 34,000 male
births.
Other non-common genetic disorders….
– Prader Willi syndrome
Prader Willi syndrome is a rare genetic disorder in
which seven genes (or some subset thereof) on the
father’s chromosome 15 are deleted or unexpressed.
This results in an inability to produce the chemical
signal that tells the body when it is “full” as a result the
person constantly feels hunger.
– Angelmen’s syndrome
Angelman’s syndrome is a rare genetic disorder that
affects the same genes as Prader Willi but on the
mother’s chromosome 15.
This results in is a neuro-genetic disorder characterized
by intellectual and developmental delay, sleep
disturbance, seizures, jerky movements (especially
hand-flapping), frequent laughter or smiling, and
usually a happy demeanor.
– Tach Sach’s syndrome
Is an autosomal recessive genetic disorder.
It causes a relentless deterioration of mental and physical
abilities that begins around six months of age and usually
results in death by the age of four.
The disease occurs when harmful quantities of cell
membrane components known accumulate in the nerve cells
of the brain, eventually leading to the premature death of
those cells.
There is currently no cure or treatment.
– Turner’s syndrome
Genetic disorder found in women caused by the
lack of a 2nd X chromosome.
Genetic counselors
– Professionals that work with prospective
parents to determine the likelihood of
producing offspring with particular traits.
– Tools used by genetic counselors
Punnett Squares
Karyotype: a picture of all 46 chromosomes
arranged in matching pairs.
Pedigree
– Chart or “family tree” that tracks which members have a
particular trait.
– Circles represent female members of the family.
– Fully shaded means a person has the trait.
– Half shaded means a person is a carrier for the trait.
– Unshaded means a person does not have the trait.
Sect. 3: Advance in Genetics
Selective breeding.
– Selective breeding is the process of selecting
a few organisms with desired traits to serve
as parents of the next generation.
– Types selective breeding techniques.
1. Inbreeding is a technique in which 2 individuals
with similar sets of alleles & traits breed in hopes
of maintaining those traits/alleles in the next
generation.
– Examples:
Domestic turkeys,
Purebred dogs,
Championship race horses.
2. Hybridization is a technique in which 2 breeders
with different sets of alleles & traits breed in
hopes of getting the best traits/alleles from both
species in the next generation.
– Disadvantage of hybrids most hybrid species cannot
reproduce.
Mule: cross between Horse & Donkey
Liger: cross between Lion & Tiger
Wolphin: cross between Dolphin & Killer Whale
Cama: cross between Llama & Camel
Clone
– A clone is an organism that has the exact
same genes as the organism from which it
was produced.
Identical twins are natural occurring clones.
Genetic engineering
– Genetic engineering is the transfer of a gene
from the DNA of one organism into another
organism in order to produce an organism
with desired traits.
– Bacterial engineering
1. Scientists remove plasmids, small rings of DNA, from
bacterial cells.
2. An enzyme cuts open the plasmid DNA. The same
enzyme removes the human insulin gene from its
chromosome.
3. The human insulin gene attaches to the open ends of
the plasmid to form a closed ring.
4. Some bacterial cells take up the plasmids that have the
insulin gene.
5. When the cell reproduce, the new cell will contain
copies of the “engineered” plasmid. The foreign gene
directs the cell to produce human insulin.
Genetic engineering has been used to incorporate genes into
plants to make them
– resistant to frost,
– produce more offspring,
– change color, texture & taste.
Genetic engineering has been used to incorporate genes into
animals to make them
– Bigger, faster, & stronger.
– Cows: produce more milk, produce more muscle tissue
Gene therapy
– Process in which scientist attempt to remove or fix a faulty gene
or chromosome by replacing it with a correctly functioning
gene.
Concerns about genetic engineering
– Long term safety effects to humans of genetically engineered
food & animals.
– Concern that people will be able to “engineer” offspring.
– Concern that “engineering” specific traits could eventually leave
organisms ill prepared to handle any future changes.
Human Genome Project
– The Human Genome Project was a multinational
scientific endeavor to study the human genome.
Genome is the term that refers to all the DNA contained in 1
cell of an organism.
– Sponsored by various world governments &
companies to determine…
1.
2.
3.
The number of genes in the human genetic code.
The function of the genes in the human genetic code.
The location of the genes in the human genetic code.
– Goal is to use this information to better understand,
diagnose, treat, and possibly prevent genetic
disorders and their effects.
– It began in 1990 and was completed in 2003.
– Total US investment over the 13 years is
approximately 3 billion dollars.