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THE HUMAN GENOME

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THE HUMAN GENOME Powered By Docstoc
					The Human Genome
Chapter 14
14.1 Human Heredity
   Karyotype:
    ◦ Photograph of chromosomes grouped
      together in their pairs.

   Sex Chromosomes:
    ◦ The 2 chromosomes that determine your sex.
    ◦ XX- Female XY-Male
   Autosomal Chromosomes:
    ◦ Also known as autosomes
    ◦ The remaining 44 chromosomes
    ◦ Each of these is denoted by a number

   All egg cells carry a single X chromosome.
    However, half of all sperm carry an X
    chromosome and the other half carry a Y
    chromosome.
Human Traits
   Pedigree Charts:
    ◦ Chart that shows relationships within a family
    ◦ This helps to show how traits are passed on
      within a family.
             Pedigree
                                                A square
                          A circle represents
                                                represents a
                          a female.
  A horizontal line                             male.
                                                               A vertical line and a
  connecting a male and                                        bracket connect the
  female represents a                                          parents to their
  marriage.                                                    children.
A half-shaded circle or
square indicates that a
person is a carrier of                                                A circle or
the trait.                                                            square that is not
                                                                      shaded indicates
                                                                      that a person
A completely shaded                                                   neither expresses
circle or square                                                      the trait nor is a
indicates that a person                                               carrier of the
expresses the trait.                                                  trait.
Genes and the Environment
   Some traits are polygenic
    ◦ Meaning that they are controlled by many
      genes

   Many personal traits are only partly
    governed by genes.
Human Genes
   Blood Groups:
    ◦ Knowing a person’s blood type is very
      important! If given the wrong blood type, they
      could die

    ◦ Most common are ABO and the Rh Blood
      groups
Blood Groups
   Rh group is determined by one gene with
    2 alleles
    ◦ Rh+ is dominant and Rh- is recessive
   ABO is more complicated:
    ◦ There are 3 alleles for this
    ◦ IA , IB , and i
    ◦ IA , IB are codominant, meaning that both
      alleles contribute to the phenotype
Phenotype                Antigen on       Safe Transfusions
              Genotype
(Blood Type              Red Blood Cell   To           From
Blood                     Antibodies   Reaction When Blood from Groups Below Is Mixed with
Group                     Present in   Antibodies from Groups at Left
(Phenotype)               Blood
              Genotypes
                                           O                A             B                  AB



                  ii       Anti-A
     O
                           Anti-B




                IA IA
     A          or         Anti-B
                IA i



                IB IB
     B          or         Anti-A
                IB i




    AB          IA I B       —
Today’s Objectives
   As a class we will be able to:
    ◦ Set up, read, and use a pedigree chart
    ◦ Understand how genes within our DNA can
      cause genetic diseases
Bellringer Questions
1.   If I have a half shaded square, what does
     that represent?
2.   How do we connect children/offspring
     to their parents?
3.   What are autosomal chromosomes?
     What are sex chromosomes?
Recessive Alleles
 Have 2 recessive alleles
 PKU (phenylketonuria): lack the enzyme
  needed to break down the amino acid
  phenylalanine (found in milk)
 Tay-Sachs Disease
Dominant Alleles
 Have at least one dominant allele
 Dwarfism
 Huntington’s Disease
Codominance
   Both alleles contribute to phenotype

   Sickle Cell
From Gene to Molecule
   For some genetic disorders, scientists are
    still working to find the answers.

   In both cystic fibrosis and sickle cell
    disease, a small change in the DNA of a
    single gene affects the structure of a
    protein, causing a serious genetic disorder.
Cystic Fibrosis
 Most common among ancestors from
  Northern Europe
 Recessive allele on Chromosome 7
 Caused by a small change
    ◦ There is a deletion of 3 bases in the middle of
      a sequence for a protein
Cystic Fibrosis
   Thus the protein folds wrong and gets
    destroyed
    ◦ Allows for Cl- to pass through the cell
      membrane and when destroyed this doesn’t
      happen
Cystic Fibrosis
Figure 14-8 The Cause of Cystic Fibrosis




The most common allele           Normal CFTR is a chloride    The cells in the person’s airways
that causes cystic fibrosis is   ion channel in cell          are unable to transport chloride
missing 3 DNA bases. As          membranes. Abnormal          ions. As a result, the airways
a result, the amino acid         CFTR cannot be transported   become clogged with a thick
phenylalanine is missing         to the cell membrane.        mucus.
from the CFTR protein.
Sickle Cell Disease
 Common among African Americans
 Sickled shape Red Blood Cells is more
  rigid than a normal cell causing them to
  get stuck in the capillaries and the
  narrowest blood vessels.
    ◦ Thus, blood flow decreases causing body
      weakness or damage to body organs.
Today’s Objectives
   As a class we will be able to:
    ◦ Set up, read, and use a pedigree chart
    ◦ Understand how genes within our DNA can
      cause genetic diseases
Exit Slip Questions
   From the pedigree we looked at today,
    will we always know the exact outcome
    of the offspring? Give an example.

   What does it mean if a disorder is sex
    linked? What does it mean if a disorder is
    autosomal dominant?
14.2 Human Chromosomes
   A human diploid cell contains more than
    6 Billion base pairs of DNA!

    ◦ Only about 2% of the DNA in your
      chromosomes functions as genes
Human Genes and Chromosomes
   Remember genes located close together
    on the same chromosomes are linked
    ◦ Meaning they tend to be inherited together
Sex-Linked Genes
   Genes are located on the Sex
    Chromosome
    ◦ More than 100 Sex-Linked Genetic disorders
      have been mapped on the X-Chromosome
Colorblindness
 Most common is red-green
  colorblindness found in about 1 in 10
  males
 Only about 1 in 100 females has
  colorblindness
Colorblindness
   Males have just one X Chromosome.
    Thus, all X-linked alleles are expressed in
    males, even if they are recessive
Colorblindness
                                             Father
                                             (normal vision)
                Normal
   Colorblind
                vision
Male

Female


                         Daughter        Son
                         (normal vision) (normal vision)
           Mother
           (carrier)


                         Daughter          Son
                         (carrier)         (colorblind)
Hemophilia
 Protein necessary for normal blood
  clotting is missing
 About 1 in 10,000 males are born with
  Hemophilia
 Can be treated by injections of normal
  clotting protein
Chromosomal Disorders
   Sometimes we have errors in meiosis

   The most common error is in non-
    disjunction
    ◦ Homologous chromosomes fail to properly
      separate during meiosis
            Nondisjunction

 Homologous
chromosomes
fail to separate


                     Meiosis I:     Meiosis II
                   Nondisjunction
Down Syndrome
   Trisomy 21
    ◦ There are 3 copies of the 21st chromosome
    ◦ About 1 in 800 babies are born with down
      syndrome
Sex Chromosome Disorders due to
Nondisjunction
   Turners Syndrome
  ◦ XO: Females are missing the 2nd X
    Chromosome
  ◦ Sterile and sex organs do not develop
 Kleinfelters Syndrome
    ◦ XXY: Males have an extra X Chromosome


   No cases of a baby born without an X
    ◦ Vital for survival of embryo
14.3 Human Molecular Genetics
   We can now test for certain genetic
    disorders
    ◦ We test for the abnormalities in the genetic
      sequence.
DNA Fingerprinting
 Tests and analyzes sections of DNA that
  have little or no function.
 These sections vary widely from one
  individual to another

   Has been used to help convict criminals
The Human Genome Project
   Began in 1990 and was finished in 2003

   The Human Genome Project is an
    ongoing effort to analyze the human DNA
    sequence.
The Human Genome Project
   E. coli contains ‘only’ 4,639,221 base pairs!

   Humans have over 6 billion base pairs!

   The human genome was sequenced by
    looking for overlapping regions between
    sequenced DNA fragments.
Gene Therapy
   Is the process of changing the gene that
    causes a genetic disorder

   In gene therapy, an absent or faulty gene is
    replaced by a normal working gene

   Not all gene therapy experiments are
    successful
Gene Therapy
   The first step in gene therapy identifying
    the faulty gene that causes the disease

   Gene therapy is successful if the
    replacement gene is transcribed in the
    person’s cells.
                                   Bone
                              marrow cell
                                            Nucleus
Normal hemoglobin gene
                         Chromosomes




     Genetically engineered                           Bone
     virus                                            marrow

				
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posted:10/23/2011
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