Genetics and Man

• CYTOGENETICS

  The study of chromosome number, structure, function, and behavior in relation to gene inheritance, organization and expression.
• Variations in Chromosome number

  Euploidy

  Polyploidy

  Aneuploidy
• Euploidy

  normal number and sets of chromosomes
• Polyploidy

  3 or more complete sets of chromosomes
• Aneuploidy

  presence of additional or missing individual chromosomes.
• Common Types of Polyploidy

  Triploidy

  Tetraploidy

  Pentaploidy
• Triploidy

  3n = 3(23) = 69
• Tetraploidy

  4n = 4(23) = 92
• Pentaploidy

  5n = 5(23) = 115
• Common Types of Aneuploidy

  Monosomy

  Trisomy
• Monosomy

  one less chromosome = (23 x 2) – 1 = 45
• Trisomy

  one additional chromosome = (23 x 2) + 1 = 47
• Turner Syndrome

  • named after Henry Turner
  • signs and symptoms may vary significantly, probably showing prenatally or at birth or during infancy and even during teen and adults years of a female.
• Mosaicism

  due to errors in cell division during early fetal development; chromosomal change in only some of the cells.
• Y chromosome material


  present in some cells together with the x chromosome (while some cells have only 1 copy of the X chromosome)
• Trisomy 21 (Down Syndrome)

  • named after John Langdon Down
  • One of the most common causes of human birth defects Symptoms vary from person to person and can range from mild to severe.
  • Persons with this condition have an increased risk of certain types of leukemia, which can also cause early death.
  • The level of intellectual disability varies, but is usually moderate. Adults with Down syndrome have an increased risk of dementia.
• (Trisomy 21) TYPES OF DOWN SYNDROME:

  1. Trisomy - 95%
  2. Translocation Down Syndrome - 3%
  3. Mosaic Down Syndrome - 2%
• Translocation Down syndrome – 3%

  • occurs when an extra part or a whole extra chromosome 21 is present, but it is attached or “translocated” to a different chromosome rather than being a separate chromosome 21.
• Mosaic Down Syndrome

  – affects about 2% of the people with down syndrome.
• (Trisomy 18) Edwards Syndrome

  • named after John Hilton Edwards
  • Congenital heart defects
  • Growth retardation
  • Dysmorphic features
  • Facial clefts
  • Severe developmental delay
  • Spina bifida
• Trisomy 18 types:

  1. Full Trisomy 18 - 95%
  2. Partial Trisomy 18 - very rare
  3. Mosaic Trisomy 18 - very rare
• (Trisomy 13) Patau Syndrome

  – named after Klaus Patau
• Types:1.Trisomy 132. Mosaicism3. Partial trisomy 13
• Mosaicism Syndrome

  • Also known as Warkany syndrome after Dr. Josef Warkany
  • A pear-shaped, bulbous nose with upturned nostrils, a protruding lower lip and large ears.
  • Spina bifida, renal and ureteral anomalies, CHD
  • Large ears, deep plantar furrows.
  • Most cases have mosaicism
  • Stiff joints with a limited range of movement; clenched or bent fingers and/or toes; deep palm and sole creases; occasionally under-developed nails: missing or small kneecaps. Typically have mild to moderate intellectual disabilities.
• Sex Chromosome Variations (Trisomy X) 47, xxx

  • Incidence 1 in 1000 female births
  • Most have learning disabilities
  • Behavioral problems common
  • Many never diagnosed.
  • Normal phenotype
  • Above average stature
• Sex Chromosome Variations - Klinefelter Syndrome (47, xxy)

  • 1:1000 male births
  • Tall structure
  • Gynecomastia
  • Hypogonadism
  • Infertility
  • Learning disabilities
  • Problems with socialization
  • Many never diagnosed.
• Sex Chromosome Variations - Jacob Syndrome (47, xyy)

  • 1/1000 newborn males
  • Most phenotypically normal
  • Normal IQ but 50% have learning disabilities (language and speech)
  • Tall stature
  • Many never diagnosed
  • Most males with this syndrome have normal sexual development and are able to father children.
  • Delayed development of motor skills (such as sitting and walking), weak muscle tone (hypotonia), hand tremors or other involuntary movements (motor tics), and behavioral and emotional difficulties are also possible.
• Factors that influence non-disjunction or premature sister chromatid separation:

  Age

  Recombination events
• The rate of Down syndrome and other trisomies increases with maternal age.
• INBORN ERRORS OF METABOLISM

  Lactase Deficiency

  PKU (Phenylketonuria)

  Classic Galactosemia (GALT deficiency)
• Lactase Deficiency

  Common in adults; occurs more often in native americans and people of Asian, African, and South American descent than among people of European descent.
• PKU (Phenylketonuria)


  AR

  Rare
• Classic Galactosemia (GALT deficiency)

  • Also known as type I is the most common and most severe form of the condition.
• BEHAVIORAL GENETICS

  • An interdisciplinary field of study concerned with the genetic basis of behavior and personality.
  • Both genes and environment interact to shape human behavior.
  • The fundamental issue is how much a role genetics do play in shaping human behaviors
  • Genes do not directly produce behaviors.
  • They produce proteins that increase the probability that a behavior will develop under certain circumstances.
  • Genes can also have an indirect effect.
  • Genes can alter your environment by producing behaviors or traits that alter how people in your environment react to you.
• Evolutionary Psychology (Sociobiology)

  • focuses upon functional explanations of how behaviors evolved.
  • Assumes that behaviors characteristic of a species have arisen through natural selection and provide a survival advantage.
  • Examples: differences in peripheral/color vision, sleep mechanisms in the brain, eating habits, temperature regulation.
• Some behaviors are more debatable regarding the influence of natural selection.
• Some behaviors are more debatable regarding the influence of natural selection.Examples:

  • Life span
  • Gender differences in sexual promiscuity
  • Altruistic behavior
• Some behavioral disorders that are influenced by genes:

  1. Alcoholism2. Schizophrenia

  3. Depression