Autosomal Recessive InheritanceBy: Joey Cisneroz

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Genetic Inheritance• 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/ aa- homozygous 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?• 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• 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 DiseaseCystic Fibrosis

• 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

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

ReferencesPictures

• www.petridish.org• biologia-lacienciadelavida.

blogspot.com• lady-rosales.blogspot.com• www.accessexcellence.org• www.mayoclinic.com

Information • http://www.ncbi.nlm.ni

h.gov/pubmedhealth/PMH0001554/

• http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002390/

• http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001167/