The Effects of Genetics

							The Effects of Genetics

 Diseases due to Chromosomal
Abnormalities and DNA mutations
            Nondisjunction
• Nondisjunction occurs when homologous
  chromosomes fail to separate during
  anaphase 1.
• The result is haploid gametes with an extra
  copy of a chromosome, or with a missing
  chromosome
• After gametes fuse, the zygote may have
  either 3 or 1 of the given chromosome.
    Nondisjunction - Trisomy
• XXX syndrome
• Occurs in 1/1,000 females
• Women can have developmental issues
  (learning disabilities, physical development).
• Every female cell develops a bar body
  anyways (so only one X chromosome is
  active), XXX females simply have 2 inactive X
  chromosomes.
    Nondisjunction - Trisomy
• Klinefelter's syndrome (XXY)
• Occurs in 1/500 men.
• Men are usually infertile, slightly more
  feminized in appearance.
   Nondisjunction - Trisomy
• XYY syndrome
• IQ lower by 12 points on average
• Average of 7cm taller
    Nondisjunction - Trisomy
• Down syndrome (Trisomy 21)
• Occurs in about 1/ 900 births
• At maternal age 20 to 24, the probability
  is one in 1562; at age 35 to 39 the
  probability is one in 214, and above age
  45 the probability is one in 19
Down Syndrome
   Nondisjunction - Trisomy
• Edwards syndrome (Trisomy 18)
• Occurs in 1 / 3,000 births
• The syndrome has a very low rate of
  survival, resulting from heart
  abnormalities, kidney malformations,
  and other internal organ disorders.
• 95% of cases result in miscarriage.
        Edward’s Symptoms
• characteristics: kidney malformations,
  structural heart defects at birth, intestines
  protruding outside the body (omphalocele)
  esophageal atresia, mental retardation,
  developmental delays, growth deficiency,
  feeding difficulties, breathing difficulties, and
  arthrogryposis (a muscle disorder that causes
  multiple joint contractures at birth)
Edward’s Syndrome
    Nondisjunction - Trisomy
• Patau syndrome (Trisomy 13)
• Occurs in 1 / 12,000 births
• As with all nondisjunctive disorders,
  mother’s age is predictive of incidence.
• There are MANY abnormalities
  associated
• Infants typically die within days.
Patau Syndrome
 Nondisjunction - Monosomy
• Turner syndrome (single X)
• Occurs in 1/ 2,500 females
• 98% of fetuses are spontaneously
  aborted (miscarriage).
• Results in short stature, webbed neck,
  and low hairlines.
  Nondisjunction - Monosomy
• Cri du chat (Monosomy 5)
• Infants have a characteristic cat cry
• Results in mental retardation,
  hyperactivity and tantrums.
       Williams syndrome
• Results from a deletion of 26 genes on
  chromosome 7.
• Individuals are very social, but lack
  “common sense.
William’s Syndrome
     Autosomal Dominant
          Disorders
• Marfans
       Autosomal Dominant
            Disorders
• Huntington’s Disease
• Globally, up to 7 people in 100,000 have the
  disorder
• Results from 36 or more CAG base repeats
  (less than 26 is normal) on a section of DNA
  on chromosome 4.
• CAG codes or Glutamine (so an extra long
  protein that functions differently).
• Results in onset of uncoordinated, jerky body
  movements and a decline in some mental
  abilities.
      Autosomal Dominant
           Disorders
• Marfan Syndrome
• Occurs in about 1/5,000 births
• Results in a defective protein in
  connective tissue - causing people to be
  taller than normal with arachnodactyly
  (spider fingers)
• Death often results from problems with
  the aorta.
Marfan Syndrome
       Autosomal Recessive
            Disorders
• Tay - Sachs
• 1 in 30 Ashkenazi Jews, French Canadians,
  and Cajuns is a recessive carrier
• Occurs when harmful quantities of a fatty acid
  derivative called a ganglioside accumulate in
  the nerve cells of the brain.
• Tay-Sachs disease is caused by a genetic
  mutation on the HEXA gene on chromosome
  15
• Children usually die by age of 5.
Tay Sachs
          Autosomal Recessive Disorders

• Sickle-cell Anemia
• Occurs in 1 in 5,000,
• Affecting mostly those of African descent.
• Beneficial in regions with malaria,
  Trypanosoma larva can’t infect sickle-cells.
• Results from a substitution (T subs for A)
  turning valine into glutamine. At the middle of
  the 6th codon on for the haemoglobin protein
  on chromosome 11.
• Under low oxygen conditions the cells
  “deflate”. They can collect in arteries, etc.
  and cause pain.
     Diagnosis - Karyotypes
• Karyotypes reveal chrmosomal
  abnormalities such as monosomy,
  trisomy,
• Also reveal structural abnormalities
  such as translocations, inversions,
  large-scale deletions or duplications
Male Karyotype
Diagnosis - Genetic Screening
• Parents may be “screened” before
  pregnancy.
• Fetus’ may be screened by sampling via
  chorionic villi or amniocentesis. Either on
  carries a risk of infection or miscarriage.
• Babies may be screened after birth via blood,
  hair, cells, etc. using Gel electrophoresis
Mutations
I told you…