Human Genetics

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Human Genetics
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Human Genetics

• Heredity
• The passing-down of traits from parent to child
  through genes, which are located in chromosomes.
  Such traits are said to be "inherited."

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Human Genetics

• Predicting Disorders
• Record keeping helps scientists use pedigree
  analysis to study inheritance patterns, determine
  phenotypes, and ascertain genotypes.

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Human Genetics

• Pedigree
• A diagram that shows the pattern of inheritance
  of a gene in a family. These diagrams can also be
  called a family tree of inheritance.

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Human Genetics

• Pedigree symbols

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• Karyotype
• A picture of the chromosomes in a cell that is
  used to check for abnormalities.

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Human Genetics

• Sex-Linked Traits
• The sex chromosomes, X and Y, carry genes for
  many characters other than gender.
• A sex-linked gene is located on either an X or a
  Y chromosome.
• Traits that are not expressed equally in both
  sexes are commonly sex-linked traits.
• Colorblindness is an example of a sex-linked
  trait that is expressed more in males than in
  females.

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Genetic Disorders

• Genetic Disorder
• A genetic disorder is a disease that is caused by
  an abnormality in an individual's DNA.
  Abnormalities can range from a small mutation in
  a single gene to the addition or subtraction of
  an entire chromosome or set of chromosomes.
• These harmful effects are produced by inherited
  mutations (defective alleles).

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Genetic Disorders

• Types of Genetic Disorders
• Autosomal Recessive Genetic Disorders
• Autosomal Dominant Genetic Disorders
• Sex-Linked Genetic Disorders
• Nondisjunction Genetic Disorders

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Genetic Disorders

• Autosomal
• An autosome is a non-sex chromosome. It is a pair
  of chromosomes that is the same in both sexes of
  a species. For example, in humans, there are 22
  pairs of autosomal chromosomes (chromosomes 1
  through 22). The X and Y chromosomes are not
  autosomal (chromosome 23).

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Genetic Disorders

• Autosomal Recessive Genetic Disorders
• Cystic Fibrosis
• Phenylketonuria
• Galactosemia

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Genetic Disorders

• Cystic Fibrosis (13,900)
• Cystic fibrosis is a genetic disorder that
  affects the respiratory and digestive systems.
• People with cystic fibrosis inherit a defective
  gene on chromosome 7.
• The protein produced by this gene normally helps
  salt (sodium chloride) move in and out of cells.
  If the protein doesn't work correctly, that
  movement is blocked and an abnormally thick
  sticky mucous is produced on the outside of the
  cell. The cells most seriously affected by this
  are the lung cells. This mucous clogs the airways
  in the lungs, and increases the risk of infection
  by bacteria.

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Genetic Disorders

• Phenylketonuria (118,000)
• Phenylketonuria is a rare metabolic disorder that
  affects the way the body breaks down protein.
• PKU is caused by a mutation in a gene on
  chromosome 12.
• The gene codes for a protein called PAH
  (phenylalanine hydroxylase), an enzyme in the
  liver. This enzyme breaks down the amino acid
  phenylalanine into other products the body needs.
  When this gene is mutated, the shape of the PAH
  enzyme changes and it is unable to properly break
  down phenylalanine. Phenylalanine builds up in
  the blood and poisons nerve cells (neurons) in
  the brain.

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Genetic Disorders

• Galactosemia (155,000)
• Galactosemia is a rare disorder that affects the
  body's ability to break down a food sugar called
  galactose.
• Galactosemia is caused by a mutation in a gene on
  chromosome 9.
• People with galactosemia are missing an enzyme
  called GATL (galactose-1-phosphate uridyl
  transferase), which normally converts galactose
  into glucose. Without this enzyme, harmful
  amounts of galactose build up in the blood.

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Genetic Disorders

• Autosomal Dominant Genetic Disorders
• Breast/Ovarian Cancer
• Huntingtons Disease
• Colon Cancer

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Genetic Disorders

• Breast/Ovarian Cancer (5-10 of patients)
• Most people who develop breast or ovarian cancer
  have no history of the disease in their family.
  In fact, only 5 to 10 percent of all breast and
  ovarian cancers are caused by inherited genetic
  factors. These rare cases typically result from
  inherited mutations on either chromosome 17 or
  chromosome 13.
• Men who inherit the defective genes are also more
  likely to develop breast and/or prostrate cancer.
  (Yes, men can get breast cancer.)

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Genetic Disorders

• Huntingtons Disease (130,000)
• Huntington's Disease (HD) is a brain disorder
  that affects a person's ability to think, talk,
  and move.
• HD is caused by a mutation in a gene on
  chromosome 4.
• Normally, the coding region of this gene contains
  the DNA sequence "CAG" repeated again and again.
  The number of times this triplet is repeated
  varies from person to person, ranging from 10 to
  26 times.
• People with HD have an abnormally high number of
  these CAG triplets, approximately 40 or more.
  Somehow the brain cells of HD patients accumulate
  clumps of protein that become toxic, resulting in
  cell death. Some patients lose more than 25 of
  their brain cells before they die.

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Genetic Disorders

• Colon Cancer (80 of patients)
• People who have a history of colon cancer in
  their family are at greater risk of getting the
  disease themselves. The risk increases when a
  relative has had the disease before age 50. These
  families are considered high-risk, because they
  may have inherited one rare genetic condition
  FAP (familial adenomatous polyposis).
• FAP is caused by mutations in a gene on
  chromosome 5.

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Genetic Disorders

• Sex-Linked Genetic Disorders
• Klinefelter syndrome
• Turner syndrome
• Fragile-X syndrome

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Genetic Disorders

• Klinefelter Syndrome (11,000)
• Klinefelter syndrome is a disorder that affects
  only males. Males normally have an X chromosome
  and a Y chromosome (XY). But males who have
  Klinefelter syndrome have an extra X chromosome
  (XXY), giving them a total of 47 instead of the
  normal 46 chromosomes.
• People with this disorder develop as males with
  subtle characteristics that become apparent
  during puberty. They are often tall and usually
  don't develop secondary sex characteristics, such
  as facial hair or underarm and pubic hair.

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Genetic Disorders

• Turner Syndrome (13,000)
• Turner syndrome is caused by a missing or
  incomplete X chromosome.
• People who have Turner syndrome develop as
  females. The genes affected are involved in
  growth and sexual development, which is why girls
  with the disorder are shorter than normal and
  have abnormal sexual characteristics.

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Genetic Disorders

• Fragile X Syndrome (13,600 males and 16,000
  females)
• Fragile X syndrome is the most common form of
  inherited mental retardation.
• A change or mutation in a gene on the X
  chromosome causes the fragile X syndrome. In
  females, these are two X's in males they are and
  X and Y. Gene responsible for fragile X syndrome
  is called the FMR1 (fragile X mental retardation
  1) gene.

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Genetic Disorders

• Nondisjunction Genetic Disorders
• Patau syndrome/Trisomy 13
• Edwards syndrome/Trisomy 18
• Downs syndrome/Trisomy 21

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Genetic Disorders

• Nondisjunction
• An event that can occur during meiosis where the
  chromosomes don't separate properly. It results
  in the developing egg or sperm cell having too
  many or too few chromosomes.

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Genetic Disorders

• Patau syndrome/Trisomy 13 (110,000)
• Trisomy 13, also called Patau syndrome, is a
  genetic disorder associated with the presence of
  extra material from chromosome 13.

• Cleft lip or Palate
• Close-Set Eyes
• (eyes may actually fuse together into one)
• Decreased Muscle Tone
• Extra Fingers or Toes
• Hernias
• Hole, Split, or Cleft in the Iris

• Low-Set Ears
• Severe Mental Retardation
• Scalp defects (absent skin)
• Skeletal (limb) Abnormalities
• Small Eyes
• Small Head
• Small Lower Jaw

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Genetic Disorders

• Edwards syndrome/Trisomy 18 (13,000)
• Trisomy 18 is a relatively common syndrome. It is
  three times more common in girls than boys. The
  syndrome is caused by the presence of an extra
  material from chromosome 18.

• Clenched Hands
• Crossed Legs
• (preferred position)
• Heart Disease
• Kidney Problems
• Low Birth Weight
• Hole, Split, or Cleft in the Iris

• Low-Set Ears
• Severe Mental Retardation
• Hernias
• Underdeveloped fingernails
• Unusual Shaped Chest
• Small Head
• Small Lower Jaw

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Genetic Disorders

• Downs syndrome/Trisomy 21 (1800)
• Down syndrome occurs when there is an extra copy
  of chromosome 21. This form of Down syndrome is
  called Trisomy 21. The extra chromosome causes
  problems with the way the body and brain develop.
  Down syndrome is the most common single cause of
  human birth defects.

• Decreased Muscle Tone
• Excessive Skin
• (Usually on the nape of the neck)
• Flattened Nose
• Separated Sutures
• Single Crease in Palm
• Small Ears

• Small mouth
• Upward slanting Eyes
• Wide, Short Hands
• Moderate Mental Retardation
• Heart Defects
• Hearing Problems
• Cataracts

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Genetic Disorders

• Nondisjunction
• Nondisjunction can occur with any chromosome, but
  often result in miscarriage. For example, Trisomy
  16 is the most common trisomy in humans,
  occurring in more than 1 of pregnancies. This
  condition, however, usually results in
  spontaneous miscarriage in the first trimester.