The Effects of Genetics

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The Effects of Genetics

• Diseases due to Chromosomal Abnormalities and DNA
  mutations

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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.

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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.

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Nondisjunction - Trisomy

• Klinefelter's syndrome (XXY)
• Occurs in 1/500 men.
• Men are usually infertile, slightly more
  feminized in appearance.

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Nondisjunction - Trisomy

• XYY syndrome
• IQ lower by 12 points on average
• Average of 7cm taller

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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

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Down Syndrome
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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.

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Edwards 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)

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Edwards Syndrome
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Nondisjunction - Trisomy

• Patau syndrome (Trisomy 13)
• Occurs in 1 / 12,000 births
• As with all nondisjunctive disorders, mothers
  age is predictive of incidence.
• There are MANY abnormalities associated
• Infants typically die within days.

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Patau Syndrome
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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.

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Nondisjunction - Monosomy

• Cri du chat (Monosomy 5)
• Infants have a characteristic cat cry
• Results in mental retardation, hyperactivity and
  tantrums.

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Williams syndrome

• Results from a deletion of 26 genes on chromosome
  7.
• Individuals are very social, but lack common
  sense.

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Williams Syndrome
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Autosomal Dominant Disorders

• Marfans

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Autosomal Dominant Disorders

• Huntingtons 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.

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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.

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Marfan Syndrome
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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.

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Tay Sachs
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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 cant 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.

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Diagnosis - Karyotypes

• Karyotypes reveal chrmosomal abnormalities such
  as monosomy, trisomy,
• Also reveal structural abnormalities such as
  translocations, inversions, large-scale deletions
  or duplications

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Male Karyotype
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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

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Mutations
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I told you