summary of Autosomal recessive inheritance for health science students ... By Abdoulwahab Mahdi Ali (Student)

1. Autosomal recessive
inheritance (presentation)
By: Abdoulwahab Mahdi Ali

2. Important concepts:
Phenotype: Observable physical properties of an organism
Genotype: Genetic makeup of an organism
Allele: Is a variant form of a gene.
Homozygous: Genotype consisting of two identical alleles of a gene for a particular trait.
Heterozygous: Different alleles of gene for particular trait.
Consanquinity: Close blood relationship.

3. Autosomal recessive inheritance
 Autosomal recessive is one of several ways that a trait, disorder, or disease can be passed
down through families.
 An autosomal recessive disorder means two copies of an abnormal gene must be present in
order for the disease or trait to develop.
 Inheriting a specific disease, condition, or trait depends on the type of chromosome that is
affected. The two types are autosomal chromosomes and sex chromosomes. It also depends on
whether the trait is dominant or recessive.
 A mutation in a gene on one of the first 22 non sex chromosomes can lead to an autosomal
disorder.
 It’s Fairly rare in populations.

5. Continue…
 Genes come in pairs. One gene in each pair comes from the mother, and the other gene comes
from the father.
 Recessive inheritance means both genes in a pair must be abnormal to cause disease.
 People with only one defective gene in the pair are called carriers. These people are most
often not affected with the condition. However, they can pass the abnormal gene to their
children.

6. CHANCES OF INHERITING A TRAIT
 If you are born to parents who carry the same autosomal recessive change (mutation), you
have a 1 in 4 chance of inheriting the abnormal gene from both parents and developing the
disease.
 You have a 50% (1 in 2) chance of inheriting one abnormal gene. This would make you a
carrier.

8. Continue…
 In other words, for a child born to a couple who both carry the gene (but do not have signs of
disease), the expected outcome for each pregnancy is:
 A 25% chance that the child is born with two normal genes (normal).
 A 50% chance that the child is born with one normal and one abnormal gene (carrier, without
disease).
 A 25% chance that the child is born with two abnormal genes (infected with the disease).

9. Characteristics of Autosomal recessive
inheritance
 males and females have the condition in roughly equal proportions.
 people with the condition are usually in one sib-ship in one generation.
 consanguinity, where both parents have one or more ancestors in common, increases the
chance that a condition presenting in a child of theirs might be due to both parents being
carriers for the same recessive gene alteration.

10. Recurrence risks
Autosomal recessive inheritance when both
parents are unaffected genetic carriers for the
condition. The faulty copy of the gene containing
a recessive mutation is represented by ‘r’; the
working copy of the gene by ‘R’.

11. Autosomal recessive inheritance when only one of
the parents is an unaffected genetic carrier for the
condition. The faulty copy of the gene containing a
recessive mutation is represented by ‘r’; the
working copy of the gene by ‘R’.

12. Autosomal recessive inheritance when one of
the parents is affected or predisposed to develop the
condition and the other parent is an unaffected non-
carrier for the condition. The faulty copy of the gene
containing a recessive mutation is represented by ‘r’;
the working copy of the gene by ‘R’.

13. Autosomal recessive inheritance when one of the
parents is affected or predisposed to develop the
condition and the other parent is an unaffected
genetic carrier for the condition. The faulty copy of
the gene containing a recessive mutation is
represented by ‘r’; the working copy of the gene by
‘R’.

14. Autosomal recessive inheritance when both
parents are affected or predisposed to
develop the condition.

15. Common autosomal recessive disorders
Common autosomal recessive disorders include:
 cystic fibrosis
 sickle cell anemia
 Tay-Sachs disease
 Gaucher disease

16. cystic fibrosis (CF)
 Cystic fibrosis (CF) is a common, inherited, single-gene disorder, in white race.
 People with CF produce mucus that is abnormally thick and sticky that can damage body
organs.
 The mucus interrupts the function of vital organs, especially the lungs, and leads to chronic
infections.
 CF also involves the pancreas and causes decreased absorption of essential nutrients and can
cause reproductive system damage.
 With improved treatment and management of the disease, affected people may live well into
adulthood. Ultimately, death most often occurs from respiratory failure. Other people with
variants of CF may have only lung involvement, sinusitis, or infertility.

17. Sickle Cell Anemia
 Sickle cell anemia is another common, inherited, single-gene disorder found mostly in African-
Americans.
 About 1 in 500 African-American babies is born with sickle cell anemia. About 1 in 12 African-
American people carries the gene for this disease.
Sickle cell disease involves the hemoglobin in the red blood cells, and their ability to carry
oxygen.
Normal red blood cells cells are smooth, round, and flexible, like the letter "O." They can
easily move through the vessels in our bodies.

18.  Sickle cells are stiff and sticky. When they lose their oxygen, they form into the shape of a
sickle, or the letter "C."
 These sickle cells tend to cluster together and can't easily move through the blood vessels.
 The cluster causes a blockage and stops the movement of healthy, normal, oxygen-carrying
blood.
This blockage is what causes the painful and damaging complications of sickle cell disease.

19.  Sickle cells live only for about 15 days. Normal hemoglobin cells can live up to 120 days.
Sickle cells risk being destroyed by the spleen because of their shape and stiffness.
The spleen helps filter the blood of infections. Sickle cells get "stuck" in this filter and die.
Due to the decreased number of hemoglobin cells circulating in the body, a person with sickle
cell is chronically anemic.

20.  The spleen also suffers damage from the sickle cells, which block the healthy oxygen-carrying
cells, after repeated blockages, the spleen is very small and does not work properly.
 Without a functioning spleen, these people are more at risk for infections.
 Infants and young children are at risk for life-threatening infections.
 Treatment includes prompt emergency care for fevers and infections, appropriate
vaccinations, penicillin, and management of anemia.

21. Tay-Sachs disease
 Tay-Sachs disease is a fatal disorder in children (usually by age 5) that causes a progressive
degeneration of the central nervous system.
 It is caused by the absence of an enzyme called hexosaminidase A (or hex A). Without hex A, a
fatty substance builds up on the nerve cells in the body, particularly the brain.
 The process begins early in pregnancy when the baby is developing.
It is not apparent until several months after the birth.
 there is no cure for Tay-Sachs.
About 1 in 27 persons of European Ashkenazi Jewish ancestry carries the Tay-Sachs gene.

22. Gaucher disease
 Many of your organs and tissues can be damaged from this disease. An enlarged liver
and spleen, as well as anemia, are common.
 Some people also have seizures and brain damage.
 The most severe type causes problems for babies before they’re born or in the days right after
birth.