Autosomal Recessive Inheritance
By: Joey Cisneroz
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Genetic Inheritance
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When each person is conceived they receive a set of
instructions called genes from each of their parents
These instructions give each person their features, light or
dark hair, brown or blue eyes, etc.
There are two common types of genes, A dominant and a
recessive gene
These genes are represented by alleles, a capital letter
represents a dominant gene (A) and a lowercase letter
represents the recessive gene (a)
These alleles are represented in pairs (AA, Aa, aa)
When two of the same type of alleles are paired together it
is a homozygous pair (AA- homozygous dominant/ aahomozygous recessive)
When there is one of each type of allele it is called a hybrid
or a heterozygous pair (Aa)
This pair becomes a dominant gene because the dominant
gene overpowers the recessive gene
Punnet Squares help show how the genes are passed down
from parents to offspring
What is an Autosome?
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An autosome is any chromosome that is not considered a sex chromosome
A human cell has 23 pairs of chromosomes, 22 of these pairs are known as
autosomes while the one remaining pair is a sex chromosome (X and Y
chromosomes)
An autosome is any of the chromosomes represented by a number 1-22
Many disorders like Downs Syndrome occur in the autosomes
Autosomal Recessive Inheritance
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A person’s DNA (genetic information) is carried
inside their chromosomes
When a person is born with a certain characteristic
they inherit it from their parents
Some people are born with a characteristic that
neither their mother nor their father show
The reason the offspring can have this characteristic
is because both their parents have heterozygous
genes
For example if the mother has brown eyes and the
father has brown eyes and their offspring has blue
eyes they must have both been carrying the blue
eye trait; therefore, the parents were both
heterozygous recessive
Autosomal Recessive disorders
• Often times the recessive trait is harmless, like the brown v.
blue eyes trait
• The blue eye trait is neither beneficial nor harmful
• In some cases, there is a trait that determines whether or not
you have a certain disease
• Three cases of this are, the sickle cell anemia disease, the
cystic fibrosis disease, and the Tay-Sachs disease
• If a person has the full affects of any of these diseases they
have homozygous recessive alleles
• If each parent has heterozygous alleles for the same disease,
there is a 25% chance each child they have will be affected by
this trait
Cystic Fibrosis and Tay-Sachs Disease
Cystic Fibrosis
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As a result of the Cystic Fibrosis disease, an
unusually thick, sticky mucus builds up in the
person’s lungs and other organs and parts of
their body
It is one of the most common life threatening
lung diseases in children and young adults
An estimated 1 in 29 Caucasian Americans are
thought to have had the gene
Most CF children are diagnosed at age 2
People diagnosed at 2 usually have a less
serious case of the disease
The disease is most harmful to the lungs and
pancreas as a result of mucus build up in
these organs
This disease can also affect the sweat glands
and, in a man, their reproductive system
Tay-Sachs Disease
• Tay-Sachs disease is a result of a
defective gene on chromosome 15
• Tay-Sachs disease is a result of the
body’s lack of hexosaminidase, a
chemical found in nerve tissues called
gangliosides
• Without hexosaminidase gangliosides
build up in nerve cells in the brain and
other cells
• Tay-Sachs disease can be infantile,
juvenile, or an adult form
• Adult forms of Tay-Sachs is very rare
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Sickle Cell Anemia
Sickle Cell anemia is one of the well known recessively
inherited diseases
This disease causes sickling of red blood cells when the
person is in a situation of low oxygen, ex. After a run
In each of the sickled cells there is an unusual form of
hemoglobin, Hemoglobin S
These cells deliver less oxygen to the body’s tissues
Unlike the other two diseases, sickle cell anemia still
affect a person who has a heterozygous pair of alleles
for that gene
The person who is a carrier but does not have extreme
sickling will lose their breath easily while doing
something active
With this trait there is a benefit, a person with a
heterozygous gene for sickle cell anemia will be less
likely to be affected by a disease like malaria that
harms red blood cells
A situation like this could be classified as incomplete
dominance
References
Information
• http://www.ncbi.nlm.ni
h.gov/pubmedhealth/P
MH0001554/
• http://www.ncbi.nlm.ni
h.gov/pubmedhealth/P
MH0002390/
• http://www.ncbi.nlm.ni
h.gov/pubmedhealth/P
MH0001167/
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Pictures
www.petridish.org
biologialacienciadelavida.blogspot.
com
lady-rosales.blogspot.com
www.accessexcellence.org
www.mayoclinic.com