Genetics

• the study of how and why chromosomal disorders occur

• Genetic disorders - are disorders resulting from a defect in the structure or number of genes or chromosomes

• Genes – are the basic units of hereditary that determine both the physical and cognitive characteristics of people

• Composed of DNA (Deoxyribonucleic acid) – the carrier of genetic information and considered to be the auto reproducing component of chromosomes

Nature of Inheritance

• A person’s genotype refers to his or her actual gene composition

• A person’s phenotype refers to his or her outward appearance or the expression of the genes.

• A person’s genome - is the complete set of genes present which is about 50,000 - 100,000

• Normal Genome:

  • 46 XX – female with 46 total chromosomes

  • 46 XY – male with 46 total chromosomes

  • 47 XX21 – female with extra chromosomes (Down Syndrome)

Inheritance of Disease

Autosomal dominant disorder

• either a person has two unhealthy genes or heterozygous

  • Homozygous dominant - a person has two unhealthy genes

  • Heterozygous – a person with differ genes (a healthy gene from the mother and an unhealthy gene from the father or vice versa), the chances are even 50%.

Disorders

1. Huntington’s Disease

   • is a progressive neurologic disorder, characterized by loss motor control and intellectual deterioration.

   • Symptoms don’t manifest until people reach 35-45 years of age

2. Fascioscapulohumeral Muscular Dystrophy

   • a disorder of muscle weakness, a form of Osteogenesisimperfecta a disorder where bones are exceedingly brittle

3. Marfan Syndrome

   • a disorder of connective tissue that results in an individual being thinner and taller than usual associated with heart disorder

   • Symptoms

     1. Tall and slender

     2. Inappropriately long arms, legs, and fingers

     3. An abnormally curved spine

Dominantly Inherited pattern is present in the family:

1. One of the parents of a child with the disorder also will have the disorder.

2. The sex of the affected individual is unimportant in terms of inheritance.

3. There is usually a history of the disorder in other family members.

Autosomal Recessive Inheritance

• a diseases that do not occur unless two genes for the disease are present

• 25% chance a child born to the couple will be disease and carrier free (homozygous dominant for the healthy gene)

• 50% chance the child will be like the parents free of disease but carrying the gene (heterozygous)

• 25% chance the child will have the disease (homozygous recessive)

Disorders

1. Cystic fibrosis

   • is an inherited disorder that causes severe damage to the lungs, digestive system and other organs in the body

   • caused by an errant gene on the 7chromosomes

2. Adrenogenitalsyndrome

   • Inherited disorder that causes excessive production of adrenal androgens which trigger body changes

     • Masculinization

     • Virilization

     • Hermophrodism

3. Albinism

   • congenital disorder characterized by complete or partial absence of pigment in the skin, eyes and hair.

4. Tay-Sachs disease

   • is an inherited disorder that causes progressive deterioration of nerve cells, mental and physical

5. Galactosemia

   • disorder that affects an individual’s ability to regulate the sugar found in milk

6. Phenylketonuria

   • cognitive challenged

   • is an inborn error of metabolism of phenylalanine resulting in cerebral damage and mental retardation

7. Limb-girdle muscular dystrophy

   • diseases that causes weakness of muscles in the arms and legs.

8. Rh Factor incompatibility

   • is a condition if a mother has Rh ( - )blood and the baby has Rh ( + ) blood

Inherited disease:

1. Both parents of a child with the disorder are clinically free of the disorder.

2. The sex of the affected individual is unimportant in terms of inheritance.

3. The family history for the disorder is negative – that is no one can identify anyone else who had it (a horizontal transmission)

4. A known common ancestor between the parents sometimes exists. Both male and female came to possess a like gene for the disorder.

X-Linked Dominant Inheritance

• transmitted only by the female sex chromosomes (X chromosomes)

Disorder

1. Alport’ssyndrome

   • a progressive chronic glomerulonephritis

Characteristics:

1. All individuals with the genes are affected (the gene is dominant)

2. All female children of affected men are affected, all male children of affected men are unaffected

3. It appears in every generation.

4. All children of homozygous affected women are affected. 50% of the children of heterozygous affected women are affected.

X-Linked Recessive Inheritance

• disorders are recessive, and inheritance of the gene from both parents is incompatible with life.

• the disease will be manifested by any male children who receive the affected gene from their mother.

Disorders

1. . Hemophilia A (blood factor deficiencies)

2. Color blindness

3. Fragile X syndrome - a cognitive challenge syndrome

4. Duchene muscular dystrophy ( Pseudohypertropic )

Assessment

1. Only males in the family will have the disorder.

2. A history of girls dying at birth for unknown reasons often exists (females who had the affected gene on both X chromosomes)

3. Sons of an affected man are unaffected.

4. The parents of affected children do not have the disorders.

Y- Linked Inheritance

• Genes responsible for features such as:

  1. Height and tooth size are found on the Y chromosome

  2. Tall stature appears to be the only consistent phenotype feature associated with having an extra Y chromosomes (karyotype 47XY Y)

• no known disease genes are inherited by Y-chromosome transmission.

Common Chromosomal Disorders

1. Trisomy 13 Syndrome (Patau Syndrome)

   • the child has an extra chromosomes 13 and severely cognitive challenged

   • Characteristics

     1. Microcephaly with abnormalities of the forebrain and forehead

     2. Microphthalmos - eyes that are smaller than normal

     3. Low-set ears

2. Trisomy 18 Syndrome (Edward’s Syndrome)

   • have three copies of 18 chromosomes, severely cognitively challenged and tend to be small for gestational age at birth.

   • Characteristics

     1. Low-set ears and small jaw

     2. Congenital heart defects

     3. Misshapen fingers

     4. Rocker-bottom feet

3. Cri-du-Chat Syndrome (46XX5p/46XY5p)

   • is the result of a missing portion of chromosomes 5, severely cognitively challenged.

   • Characteristics

     1. Wide - set eyes, downward slant palpebral fissure of the eye

     2. Small head

4. Turner Syndrome (Female) (45X0)

   • Gonadal Dysgenesis

   • a chromosomal condition has only one functional X chromosomes

   • Charcteristics

     1. Short in stature and has small and nonfunctional ovaries.

     2. Secondary sex characteristics do not develop at puberty.

     3. Webbed short neck

     4. Hairline at the nape is low set

     5. Congenital anomalies (Aorta and Kidney disorders

5. Klinefelter Syndrome (47XXY)

   • are males with an extra X chromosomes

   • Characteristics

     1. Secondary sex characteristics do not develop.

     2. Small testesthat produce ineffective sperm

     3. Affected individuals tend to develop gynecomastia.

     4. Increase risk of male breast cancer

6. Fragile X Syndrome (46XY23q)

   • it is an Xlinked disorder in which one X chromosomes is defective

   • Characteristics

     1. Maladaptive behaviors such as hyperactivity and autism.

     2. Reduced intellectual functioning with deficits in speech and arithmetic.

     3. Large head, long face with high forehead, prominent lower jaw, and large protruding ears.

     4. Hyper extensive joints and cardiac disorders

     5. Enlarged testicles after puberty

7. Trisomy 21 Syndrome (Down Syndrome)

   • chromosomal abnormality, the number of children born with the disorder is less as many women choose to end pregnancies when diagnosis is made

   • Characteristics

     1. Broad and flat nose.

     2. Eyelids with extra fold of tissue at the inner canthus.

     3. Neck is short, back of the head is flat, low-set ears.

     4. Short, thick , little finger often curved inward, wide space between the first and second toes.

     5. Peculiar crease of the palm