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1. Prepared by Hamze Abdilahi Ali
University: Red Sea University
Faculty: Education
Depart; Bochemistry
course; genetics
Contect
Definition of genetic disorder
Types of genetic dis order
Mitochondrial inheritance
Chrommosome disorder and types

2. Definition of genetic disorder
Genetic disorders are conditionsTrusted Source that occur as a result of changes
to or mutations in DNA within the body’s cells.
Most cells in the body contain long strands of DNA that provide the cell with
instructions. Each DNA strand is tightly coiled around a protein called a
histone. This coiled structure is called a chromosome.
Chromosomes contain small sections of DNA called genes. These genes
provide the body with a specific set of instructions. Each human cell normally
contains 23 pairs of chromosomes, with one of each pair provided by each
parent. Therefore, a person has two copies of every gene.

3. Cont…
• A change or fault in the DNA can cause a genetic condition. Since
genes pass from parent to child, these disorders may be heritable.
However, not everyone with a genetic condition in their family will
experience symptoms of the disorder.
• Genetic conditions can affect any gene or chromosome. This means
that there are a wide range of genetic disorders, each causing various
symptoms.

4. • Development
• Genetic conditions tend to run in families. Parents pass genes on to their children, and some of
these genes may contain the basis of a genetic disorder.
• However, each parent only passes down half of their genes. The version of each gene that a parent
passes down is known as an allele.
• If two alleles from each parent differ, the body may only take instructions from one of them. The
allele that the cell takes instructions from is known as the dominant allele. The other is known as the
recessive allele.
• Some genetic conditions are carried by a dominant allele, while others are carried by a recessive
allele. Generally, a person will only inherit a particular genetic disorder if they have at least one
dominant allele for the disorder or two recessive alleles for the disorder.

5. 1. Single inheritance
A single inheritance, or monogenic, disorder is a condition that results from a fault within a
single gene. The sections below will outline some examples of single inheritance conditions.
Huntington’s disease
Huntington’s disease Huntington's disease is a condition that stops parts of the brain
working properly over time. Is degenerative brain disorder that causes:
 uncontrolled movements
 emotional disturbances
 cognitive decline
Huntington’s disease develops due to a mutation on a dominant allele within chromosome 4.

6. Dominant diseases
Dominant diseases are single gene disorders that occur in the heterozygous
state – when an individual has one mutant? copy of the relevant gene and
one healthy copy.
An example of a dominant single gene disorder is Huntington’s disease?,
which is a disease of the nervous system.

7. Recessive diseases
Recessive diseases are single gene disorders that only occur in the
homozygous state – when an individual carries two mutant versions
(alleles) of the relevant gene.
Recessive diseases are more difficult to trace through family.
because carriers of a mutant allele do not show symptoms of the disease.

8. X-linked disorders
• X-linked disorders are single gene disorders that result from the
presence of a mutated gene on the X chromosome?.
• Because females (XX) have two copies of the X chromosome but
males (XY) only have one copy, X-linked disorders are more
common in males. If a male’s single copy on the X chromosome is
mutated he has no healthy copy to restore healthy function.

9. X-linked recessive diseases
Examples of X-linked recessive disorders include red-green colour
blindness, haemophilia and the Duchenne muscular dystrophy?.
X-linked recessive disorders are much more common in males than
females because two copies of the mutant allele are required for the
disorder to occur in females, while only one copy is required in males.

10. Sickle cell diseases
Sickle cell diseases (SCDs) are a group of conditions that affect red blood cells.
Sickle cell anemia is a type of SCD in which the red blood cells that transport oxygen to the
body’s tissues are misshapen. Their unusual shape means that they are less able to transport
oxygen and more likely to clump together.

11. Cont..
Clumps of these blood cells may block a blood vessel, potentially causing:
 pain
 infections
 acute chest syndrome
 stroke
SCDs occur as a result of mutations in the HBB gene. This gene provides
instructions for the production of red blood cells.
SCDs are recessive. This means that a person would need to inherit two alleles
containing the mutation in order to have the disorder.

12. Muscular dystrophies
• Muscular dystrophies are a group of genetic conditions that cause muscle damage and weakness over time.
They are due to mutations on the DMD gene.
• Muscular dystrophies are X-linked disorders, meaning that they affect a gene on the X chromosome. These
conditions are more common in males. This is because males have one X chromosome and one Y chromosome,
whereas females have two X chromosomes. In females, the unaffected X chromosome can counteract the
affected one, but in males, there is not another X chromosome to do this.

13. 2. Multifactorial inheritance
• Multifactorial inheritance disorders (MIDs) are conditions that develop due
to a combination of genetic factors and environmental or lifestyle factors.
 These diseases also are called complex diseases.
 Although complex diseases tend to run in families, unlike single gene
disorders, they do not have clear-cut patterns of inheritance so it is difficult
to predict a person’s risk of inheriting or passing on these diseases.
 Because they can be caused by both genetic and environmental factors,
complex diseases can be difficult to treat.

14. Some of these non-genetic factors may include:
 smoking
 drinking alcohol
 eating an unhealthful diet
 not getting enough sleep
 living in an area that has high levels of air
pollution

15. Cont…
Some conditions that may fall into the category of MIDs include:
 asthma
 heart disease
 diabetes
 certain cancers
 schizophrenia
 Alzheimer’s disease
 multiple sclerosis

16. 3. Chromosomal abnormalities
• Chromosomal abnormalities are problems that affect a chromosomeTrusted
Source. Chromosomal abnormalities can involve:
 having a missing chromosome
 having an extra chromosome
 having a chromosome that has some kind of structural abnormality
• Chromosomal abnormalities usually occur when there is an error as a cell is
dividing. These errors usually occur within the egg or sperm, but they can also
happen after conception.
• It is possible to inherit a chromosomal abnormality from a parent. However,
some develop within a person for the first time.
• The sections below will outline some examples of chromosomal abnormalities.

17. Down syndrome
Down syndrome is a type of chromosomal abnormality that affects intellectual and physical
development.
• Down syndrome occurs when a person receives an extra copy of chromosome 21Trusted
Source. This means that each cell within the body contains three copies of chromosome 21
instead of the usual two copies.

18. Wolf-Hirschhorn syndrome
• Wolf-Hirschhorn syndrome is a chromosomal abnormality that can affect the entire body.
The major features of this condition include:
 delayed growth and development
 reduced muscle tone
 intellectual disabilities
 Seizures
• Wolf-Hirschhorn syndrome develops due to a deletion of a section of chromosome 4. Most
cases occur for the first time within the person who has the disorder. However, it is also
possible for a person to inherit the condition from a parent who has the chromosomal
abnormality.

19. Mitochondrial inheritance
• Mitochondria are biological structures that exist inside the body’s cells.
They generate most of the energy that the cells need to carry out their
biochemical reactions.
• Mitochondrial disorders are a group of genetic conditions that affect DNA
within the mitochondria themselves. These DNA mutations result in the
mitochondria failing to produce enough energy to sustain the body’s cells.
• Mitochondrial disorders can affect any organ or part of the body. The
symptoms a person experiences will depend on the part of the body the
disorder affects.

20. Some possible symptoms of mitochondrial disorders include:
 poor growth
 muscle weakness
 loss of muscle coordination
 visual problems
 hearing problems
 developmental delays
 intellectual disabilities
 autism spectrum disorder
 diabetes
 heart, liver, or kidney disease
 respiratory disorders
• Mutations in mitochondrial DNA are inherited maternally. This means that only
a mother can pass down mitochondrial disorders.

21. What is a chromosome disorder?
• A chromosome disorder results from a change in the number or structure of
chromosomes.
 Each of our chromosomes? has a characteristic structure and number.
• Numerical abnormalities
 The most severe chromosome disorders are caused by the loss or gain of
whole chromosomes, which can affect hundreds, or even thousands,
of genes, and are usually fatal.

22. Structural abnormalities
 This is when large sections of DNA are missing from or are added to a
chromosome.
 Structural abnormalities can take several forms.
 Deletion: a mutation causing part of the chromosome to be missing.
 Duplication: a mutation causing part of the chromosome to be
repeated, resulting in extra genetic material.

23. Cont…
 Translocation: a mutation causing one portion of a chromosome to be
moved to a different part of the chromosome (intrachromosomal) or to a
different chromosome altogether (interchromosomal). There are two key
types:
 reciprocal: segments from two different chromosomes are exchanged
 Robertsonian: an entire chromosome attaches to another.
 Inversion: a mutation resulting in a portion of a chromosome being in
the opposite orientation (inverted).
 Ring: when a portion of a chromosome has broken off and formed a
circle or ring