Autosomal Recessive Inheritance

1. Autosomal Recessive Inheritance By: Joey Cisneroz 1 2 1

2. 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

3. 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

4. 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

5. 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

6. Cystic Fibrosis and Tay-Sachs Disease 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 hexosaminidasegangliosides 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 Cystic 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

7. 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

8. References Pictures • www.petridish.org • biologia-lacienciadelavida.blogspot.com • lady-rosales.blogspot.com • www.accessexcellence.org • www.mayoclinic.com Information • http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001554/ • http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002390/ • http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001167/