Human Genome

1
Human Genome

• Chapter 14
• Sections 1-3

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14-1 Human Heredity

• Karyotype a picture of chromosomes arranged in
  homologous pairs.
• Humans have 46 chromosomes
• 23 from the male
• 23 from the female
• 44 autosomes
• 2 sex chromosomes
• Autosomal Chromosome (Autosomes) the 44
  chromosomes in a Karyotype that are not sex
  chromosomes.
• Sex Chromosomes- determine an individuals sex
• Females have 2 copies of a large X chromosome.
• Males have 1 X 1 small Y chromosome.

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Female Human Karyotype Autosomes Chromosomes
1-22Sex Chromosomes Chromosome Pair 23
Showing 2 X Chromosomes
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Male Human Karyotype Showing and X Y Chromosome
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Male vs. Female

• Males and Females are born in a roughly 5050
  ratio because of the way in which sex chromosomes
  segregate during meiosis.
• Females produce human egg cells that carry a
  single X chromosome.
• The female inherits 1 copy of every gene located
  on each X chromosome.
• Half of all sperm cells carry an X chromosome and
  half carry a Y chromosome.
• (50 XX, 50XY)

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Mendelian Genetics

• Biologists must identify an inherited trait
  controlled by a single gene.
• Establish that the trait is inherited and not a
  result of environmental influence.
• Study how the trait is passed from one generation
  to the next.
• Use a Pedigree Chart.

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Pedigree Chart

• Pedigree chart that shows the relationships
  with in a family.
• Ex. Pg. 342, fig. 14-3
• The inheritance of a certain trait in a family
  can be traces using a pedigree.
• It shows how a trait can be passed from one
  generation to the next.
• It determined whether an allele is dominant or
  recessive.
• The circle represents a Female and the square
  represents a Male.

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Pedigree Chart
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Human Genetic DisordersPg. 345, fig. 14-6

• PKU (Phenylketonuria)
• One of the first discovered.
• Lacks and enzyme that breaks down an amino acid
  found in milk.
• When phenylalanine builds up, it causes mental
  retardation.
• Caused by a recessive allele from both parents.

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Human Genetic Disorders

• Cystic Fibrosis
• Result of a deletion of 3 bases in the middle of
  the protein sequence which causes the protein to
  fold improperly.
• It messes up the order because bases are removed.
  
• Digestive problems thick, heavy mucus clogs the
  lungs.
• Caused by a recessive allele from both parents.

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Human Genetic Disorders

• Sickle Cell Anemia
• Red blood sell are shaped like sickles.
• Shape causes cells to get stuck in the vessels
  and blood not to flow.
• Tissues are damaged and severe weakness.
• Linked to malaria in Africa.
• Only 1 DNA base is changed in the allele.
• Codominant allele.

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Sex Linked Genes

• Genes that are located on the X and the Y
  chromosomes. Pg. 350, fig. 14-12
• X Chromosome more than 100 sex linked genetic
  disorders occur here.
• Y Chromosome smaller and has fewer disorders.
• Colorblindness, Hemophilia, Muscular Dystrophy
  are expressed in males even if they are
  recessive.
• To appear in a female, it must have 2 copies.
• Are passed from fathers to daughters to then to
  their sons.

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Sex Linked Genetic Disorders

• Colorblindness
• Genes are defective on the X chromosome causing
  the inability to distinguish certain colors.
• Red Green - 110 males, 1100.
• Males have 1 X chromosome so all alleles are
  expressed even the recessive.

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Sex Linked Genetic Disorders

• Hemophilia
• Problem on the gene that controls blood clotting.
• Protein missing.
• 110,000 males
• May lead to death from minor cuts or internal
  bleeding from bumps.
• It can now be treated with injections.

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Sex Linked Genetic Disorders

• Duchenne Muscular Dystrophy
• Progressive weakening and loss of skeletal
  muscle.
• 13,000 males born in U.S.

16
X Chromosome Inactivation

• Since males only have 1 X chromosome, the female
  has to make adjustments for having 2 X
  chromosomes.
• In females one X chromosome is randomly turned
  off.
• It forms a dense region in the nucleus called a
  Barr body.
• Males dont have Barr bodies because their X
  chromosome is active.
• Ex. Calico Cats- X chromosome carries the allele
  for coat color and can carry more than 1 color.
  The X chromosome is turned off in many different
  places causing several colors to appear. Anytime
  you see a cat with multiple colors, it will most
  likely be female. Males are only 1 color

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Chromosomal Disorders

• Nondisjunction most common error to occur in
  meiosis. Pg. 352, fig. 14-15
• Not coming apart
• If the chromosomes do not pull apart, an abnormal
  numbers of chromosomes find their way into the
  gametes throwing off the number and order.
• Involves autosomes, sex chromosomes, and
  homologous chromosomes.
• Downsyndrome Pg. 353, fig. 14-16
• An extra copy of chromosome 21(3 copies
  trisomy)
• 1800 babies in the U.S.
• Produces mild severe mental retardation.

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Karyotype Showing Down Syndrome
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Sex Chromosome Disorders

• Caused by Nondisjunction
• Turners syndrome female inherits only 1 X
  chromosome. Women is sterile her sex organs
  dont develop.
• Klinefelters syndrome extra X chromosome
  interferes with meiosis prevents reproduction.
  Ex. XXXY, XXXXY.
• As long as a Y is present, the offspring will be
  male.

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Karyotype Showing Kleinfelters Syndrome
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14-3 Human Molecular Genetics

• DNA Fingerprinting individuals are identified
  by analyzing sections of DNA.
• No 2 people, except identical twins, have exactly
  the same DNA.
• Determine whether blood, sperm, hair, or other
  materials left at crime scene matches suspects.
• 1990- Human Genome Project Goal was to identify
  the DNA sequence for the entire DNA in a human
  cell.
• 2000- Human Genome was sequenced by looking for
  overlapping regions b/w sequenced DNA fragments.

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DNA Fingerprints from a Murder Case
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Human Genome

• Able to find causes of genetic disorders.
• Used to cure genetic disorders by using gene
  therapy.
• It cannot tell if an allele is dominant or
  recessive.