Human Heredity by 7B4G21r


									The Human Genome
    Biology --- Mrs. Volin

    Photograph of chromosomes grouped in
Humans have 46 chromosomes
   2 sex chromosomes
      XX or XY

   44 autosomes

   46 XY = male
    46 XX = female
   All egg cells are 23X

   Half sperm cells are 23Y
    Half sperm cells are 23X

So half of zygotes are 46XY and half of
  zygotes are 46XX
Pedigree chart

     Used by geneticists to track inherited
        Colorblindness

        Hemophilia

     Helpful to parents understanding probability
      of their child having an inherited disorder
     Pedigree – a chart that shows relationships in a family

                                 A circle represents   A square represents
                                 a female.             a male.               A vertical line and a
  A horizontal line connecting                                               bracket connect the
  a male and female                                                          parents to their children.
  represents a marriage.

       A half-shaded circle                                                  A circle or square
       or square indicates                                                   that is not shaded
       that a person is a                                                    indicates that a
       carrier of the trait.                                                 person neither
                                                                             expresses the trait
                                                                             nor is a carrier of
           A completely                                                      the trait.
           shaded circle or
           square indicates
           that a person
           expresses the

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                  Pedigree chart

                         Pedigree chart

What are the genotypes of the two parents on the left in the second row?
                  Pedigree chart

                         Pedigree chart

What are the genotypes of the two parents on the left in the second row?
Answer: They must both be heterozygous because they have a child
with the recessive phenotype who must have received two copies of the
recessive allele.
Blood Types are inherited
   Using wrong blood type for a transfusion can be
   Two major blood groups
      ABO blood groups

      Rh blood groups
• Type AB … universal acceptors
• Type O …. universal donors
                               ABO Blood Groups

                                      Antigen on            Safe Transfusions
           (Blood Type    Genotype   Red Blood Cell
                                                       To                 From

                   • A and B are codominant alleles.
                   • O is recessive
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Blood type frequency in total
 O 46%
 A 40%
 B 10%
 AB 4%
Rh blood grouping
   Rh factor:
          Rh group determined by a single gene with 2 alleles:
                + (dominant), and – (recessive)
          Rh-positive people are Rh+/Rh+ or Rh+/Rh-
          Rh-negative people are Rh-/Rh-
Answer these questions:
1.   What blood types would you expect the children
     to have if the parents are type A and type B, with
     genotypes of IAi and IBi?

2.   If both parents have Rh+ blood, is it possible that
     they could have a child with Rh- blood? Explain.

3.   Could a child with type A blood have parents
     that have type O and type B blood? Why or why
Answer these questions:
1.   1 AB : 1A : 1B : 1O

2.   Yes, if both are heterozygous (+/-), there is a 1 in
     4 chance that a child will be Rh-

3.   Yes. A parent combination of IB/IB and i/i could
     have children with type O and type B blood.
     Also, a parent combination of IB/i and i/i could
     have children with type O and type B blood.
Do you know your blood type?
Sex-linked genetic disorders
   Genes for some disorders are located on the X
    (Y chromosome small: only carries a few genes)

   All X-linked alleles are expressed in males
      Even though they only have one X chromosome

      Even if the allele is recessive

   Some X-linked genetic disorders
      Colorblindness

      Hemophilia

      Duchenne muscular dystrophy
Disorders caused by co-dominant alleles
   Sickle Cell Disease
      Point mutation on

       chromosome 11---
      replaces glutamic acid
       with valine

       RBCs have sickle shape

       Decreased capacity to carry
        oxygen; painful

       1/500 African Americans
Disorders caused by recessive alleles

   Cystic fibrosis
     Characterized by production of thick
      mucus that clogs lungs
     Only ½ survive into their 20s

     Mostly found in families of Northern
      European descent
     Caused by recessive allele on
      chromosome 7
                               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.

 Deletion of 3 bases

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Disorders caused by recessive
   PKU --- Phenylketonuria
      Individuals with this disorder cannot

       metabolize phenylalanine
      Buildup of phenylalanine in tissues can cause

       mental retardation
      Babies tested shortly after birth

      Treated by low-phenylalanine diet

      Caused by recessive allele on chromosome 12
Disorders caused by recessive
   Tay-Sachs disease
     Causes lipid buildup in brain cells;

      death in early childhood
     Found mostly in Jewish families of

      central- or eastern-European descent
     Prospective parents can be tested for the
      recessive allele
    Disorders caused by dominant alleles
   Huntington’s Disease
       Caused by a dominant allele for a
        brain protein
       Does not appear until middle life
       Symptoms
          Degeneration of brain cells

          Mental deterioration

          Emotional disturbances

          Uncontrolled movements
  Anerror during meiosis which causes
  some chromosomal disorders
Disorders caused by
nondisjunction: Down Syndrome
   Trisomy of chromosome 21 (an individual
    receives 3 copies of chromosome #21)
       caused by nondisjunction of chromosome #21

   Symptoms
      Learning difficulties/Mental retardation

      Heart problems

      Hearing problems
Disorders caused by nondisjunction:
Klinefelter’s Syndrome
 Extra X chromosome in males: 47XXY,
  or rarely, 47XXXY or 47XXXXY
 Symptoms
    Problems of reproductive system/treated
     with testosterone
    Tall in stature
Disorders caused by nondisjunction:
Turner’s Syndrome
 X-monosomy or 45X in females
    Only one X chromosomes is inherited

     during oogenesis
 Symptoms
    Short stature

    Problems of reproductive system (women
     are usually sterile)
Other disorders: Edward Syndrome

  Trisomy 18
  Heart problems, multiple other problems
Other disorders: Cri-du-chat syndrome
   Deletion of part of chromosome 5
   Characteristic cry of infants
   Symptoms
      Low birth weight and poor growth

      Severe cognitive, speech, and motor delays

      Behavior problems such as hyperactivity,
       aggression, tantrums, and repetitive movements
      Unusual facial features which may change over
The Human Genome Project
            Human Genome Project

• Identify all the approximate 30,000 genes in human

• Determine the sequences of the 3 billion base pairs
that make up human DNA
• Store this information in databases,
• Improve tools for data analysis,

• Transfer related technologies to the private sector,

• Address the ethical, legal, and social issues that may
arise from the project.
Human Genome Project
 Began in 1990
 Completed April 2003

 Diagnose disorders
 Treat disorders
 Prevent disorders
Current research
 National Human Genome Research Institute
  in Bethesda, Maryland
 Scientists are “mining” genomic data
  (like panning for gold)
 Powerful computer programs are used to
  compare the genomes of tens of thousands of
  persons --- half of them sick and half well ---
  to compare genetic sequences
Recent discoveries
    Breast cancer
    Colon cancer

    Rheumatoid arthritis

    Bipolar disorder

    Macular degeneration

    AIDS

    Diabetes
BBC News: On this day in 1953 . . .
   Scientists describe 'secret of life‘
    “ Two Cambridge University scientists have published their
    answer to one of the most fundamental questions of biology -
    how do living things reproduce themselves?

    In an article published today in Nature magazine, James D
    Watson and Francis Crick describe the structure of a chemical
    called deoxyribonucleic acid, or DNA.

   DNA is the material that makes up genes which pass hereditary
    characteristics from one parent to another.

   In short, it consists of a double helix of two strands coiled
    around each other. The strands are made up of complementary
    elements that fit together and when uncoiled can produce two
    copies of the original. “

 Celebrates Watson and Crick’s discovery of
  the structure of DNA
 The completion of the Human Genome

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