AUTOSOMAL DISORDERS

PATTERNS OF INHERITANCE IN FAMILIES 1

A pattern of inheritance can be predicted by studying alleles and how they work together to produce traits

GENES; these are units of heredity. They contain enough information to produce a complete protein, they control traits expressed in an individual

CROMOSOMES; They carry the genes on specific points called loci

ALLELES; these are forms or variations of a gene. They occupy the same position on a chromosome i.e same locus and control the same trait but are variations of a trait, so a variation of a gene is an allele of the gene

Ø  AUTOSOMAL DOMINANT ALLELE; These are traits that are inherited in a dominant fashion i.e they find expression even if its only present in one copy of the chromosome. These traits are found on the autosomal chromosomes. These traits affect the male and female child equally. Disorders as a result of autosomal dominant allele are rare because the affected people do not live long enough to get to reproduce and pass on the disease to their offsprings. Some examples of these disorders are; HUNTINGTON’S DISEASE, NEUROFIBROMASTOSIS,TUBEROSCLEROSIS, ALZHEIMER’S DISEASE, FAMILIAL HYPERCHOLESTEROLEMIA  etc.

Ø  HUNTINGTON’S DISEASE; this is a disease caused by a dominant allele. It is not usually expressed until the age of 30 or 40 years.the protein Huntingtin is the protein in charge of this didorder and if present it attacks the brain cells degenerating it. This dominant gene is found on chromosome 4. It is characterized by chorea, problemswith coordination, judgment and thinking due to degeneration of the nerve cell at frontal lobe, and also at the cerebellum ( jerkin muscles, slurred speech, swallowing difficulty, loss of balance, incapacitation, pneumonia or heart failure) and finally death. It is not gender biased i.e it affects male and female eqully when being passed down from parents to offspring. This chromosomal disorder is one of the few autosomal disorders that can survive into reproductive age of the carrier since it doesn’t show up until an older age

Ø  NEUROFIBROMASTOSIS; This is also called elephant man disease. The affected individuals usually have 6 spots which have the tendency to increase in size, number and darkness, nerve cells form bening tumors, there may be learning disability, hyperactivity. It is usually mild, but sever cases occur whichcan lead to death. It occurs on chromosome 17.

2.AUTOSOMAL RECESSIVE; These are chromosomal diseases that appear on the non sex chromosomes. They cannot be expressed unless there are two copies of the gene, if not it will be suppressed by a normal gene present making the individual a carrier ( this gene may later on be passed down to later generation offsprings).

Ø  CYSTIC FIBROSIS;  This is caused by a recessive gene found on chromosome 7. It causes the formation of  mucus clogs along the breathing passage ways and also digestive difficulties. It is equally distributed in male and female children. Common among Caucasian

Ø  TAY SACHS; This is due to a defective enzyme which digests fatty material. This disease causes the clustering of fatty materials around the neurons of affected individuals which will lead to paralysis on the long run. It is common amon the Jewish population and amon the Frenc- Canada population. Carriers are resuistant to tuberculosis.

Ø  PHENYLKETONURIA; This disease is due to the inanbility of a person’s body to break down the amino acid phenylalanine and so a gradual build up of this amino acid in the body and interfere with the nervous system.

Ø  SICKLE CELL ANAEMIA; this is a chromosomal disease caused by a gene found on chromosome 11. It only occurs when there are two copies of the gene. Here we have one DNA base different ( precisely the A changed to T). this change causes an abnormality in the  protein structure for heamoglobin ( responsible for oxygen in blood). So in cases of low oxygen level, the red cells take abnormal shapes ( usually sickle shape) which causes difficulty in blood flow, pain during exercise and sticking of these abnormal cells to organs, internal haemorrhaging, jaundice. Carriers of this traits (recessives) are resistant to malaria.

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