This document provides an introduction to genetic disorders. It defines key genetic terms like alleles, dominant and recessive alleles, and Punnett squares. It then describes the main types of genetic disorders: single-gene disorders caused by one gene, multifactorial disorders caused by multiple genes and environment, chromosomal disorders from abnormalities in chromosomes, and mitochondrial disorders from mutations in mitochondrial DNA. Examples are given for each type of genetic disorder.

1. INTRODUCTION
TO
GENETIC DISORDERS
Presented By :
Velo, John R.
DMD2D

2. What is an Allele?
 an alternative form of a gene located at a specific
position on a specific chromosome.
 These DNA codings determine distinct traits that
can be passed on from parents to offspring.
 May be dominant or recessive
 The process by which alleles are transmitted was
discovered by Gregor Mendel and formulated in
what is known as Mendel's law of segregation.

3. Difference between a dominant and
recessive allele
 If the two alleles from both parents are :
 Similar : homozygous offsprings
 Different : heterozygous
 the stronger of the two will show up in the
offspring while the weaker one is masked

4. Difference between a dominant and
recessive allele
 Dominant Allele
 A gene (allele) which is expressed clinically in the
heterozygous state
 In a dominant disorder, only one mutant allele need be
present as it masks the normal allele
 Recessive Allele
 A gene (allele) which is only expressed clinically in the
homozygous state
 can be suppressed if present with a dominant gene and will
not show it's character in presence of a dominant gene
 Recessive alleles or genes will only show up if the offspring
inherits recessive copies of the trait from both parents

5. Difference between a dominant and
recessive allele
 Dominant genes are usually the ones that are oftentimes
observed in an offspring and passed down to subsequent
generations while recessive genes will only show for a few
generations and eventually disappear.
 Dominant genes are represented by capital letters and
recessive genes are represented by small letters.
 There are three combinations of genotypes or alleles:
 AA (receives dominant traits from both parents),
 Aa (receives a dominant trait from one parent and a recessive
trait from the other), and
 aa (receives recessive traits from both parents)

6. What is a Punnett Square?
 a diagram that is used to predict an outcome
of a particular cross or breeding experiment
 is visual representation of Mendelian
inheritance

7. How is a trait transmitted?

8. Types of Genetic Disorders :
 Genetic disorder - disease caused by
abnormalities in an individual’s genetic
material (genome).
 The four different types of genetic disorders
are :
 (1) single-gene,
 (2) multifactorial,
 (3) chromosomal, and
 (4) mitochondrial

9. (1) Single-gene (Mendelian or
monogenic)
 caused by changes or mutations that occur in the
DNA sequence of one gene.
 Genes code for proteins, perform most life
functions, and make up the majority of cellular
structures. When a gene is mutated, it's protein
product can no longer carry out its normal
function, a disorder can result.
 Some examples are cystic fibrosis, sickle cell
anemia, Marfan syndrome, Huntington’s
disease, and hereditary hemochromatosis.

10. Examples of Single-Gene Disorders
B.
A.
C.
A. Marfan’s Syndrome
B. Cystic Fibrosis
C. Huntington’s Disease

11. (2) Multifactorial (complex or
polygenic)
 caused by a combination of environmental
factors and mutations in multiple genes.
 Examples include heart disease, high blood
pressure, Alzheimer’s
disease, arthritis, diabetes, cancer, and
obesity
 Multifactorial inheritance is also associated
with heritable traits such as fingerprint
patterns, height, eye color, and skin color.

12. (3) Chromosomal
 Chromosomes - distinct structures made up of DNA
and protein, are located in the nucleus of each cell
 Because chromosomes are carriers of genetic
material, such abnormalities in chromosome
structure as missing or extra copies or gross breaks
and rejoinings (translocations) can result in disease.
 Examples include Down syndrome or trisomy
21, Turner syndrome (45,X), Klinefelter syndrome
(47, XXY) and cri du chat syndrome, or the "cry of
the cat" syndrome (46, XX or XY, 5p-).

13. Examples of Chromosomal
Disorders

14. (4) Mitochondrial
 This relatively rare type of genetic disorder is caused
by mutations in the nonchromosomal DNA of
mitochondria.
 Examples of mitochondrial disease include:
 an eye disease called Leber's hereditary optic atrophy;
 a type of epilepsy called MERRF which stands for
myoclonus epilepsy with Ragged Red Fibers; and
 a form of dementia called MELAS for mitochondrial
encephalopathy, lactic acidosis and stroke-like episodes