Biology - Chp 14 - Human Heredity - PowerPoint
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Biology - Chp 14 - Human Heredity - PowerPoint Biology - Chp 14 - Human Heredity - PowerPoint Presentation Transcript

  • Chapter 14 Human Heredity
  • 14-1 Human Heredity
    • Scientists once knew much less about humans then about other “model” organisms such as fruit flies and mice
    • With the completion of the Human Genome Project scientists are on verge of understanding human genetics at least as well as they understand that of some other organisms
  • Human Chromosomes
    • To analyze chromosomes, cell biologists photograph cells in mitosis
    • Chromosomes are fully condensed and easiest to see during metaphase
  • Karyotype
    • A picture of chromosomes arranged in order
    • We all began life when a haploid sperm fertilized a haploid egg carrying just ________ chromosomes each.
    • The _________________________ zygote or fertilized egg contained the full complement of __________ chromosomes
    23 Diploid 46
  • Sex Chromosomes
    • Determine an individuals sex
    • Females: XX
    • Males: XY
    • The regular 44 chromosomes are known as autosomes
  • Q: Why are males & females born in a roughly 50:50 ratio?
    • A: All egg cells carry a single _______ chromosome. However, half of all sperm carry an _______ chromosome, the other half carry a ________ chromosome
    X X Y
  • Human Traits
    • In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene
    • Then, they have to study how the trait is passed from one generation to the next
  • Pedigree
    • A chart which shows the relationship within a family
    • Most human traits are not coded for by single genes
    • Also, many traits are strongly influenced by environmental factors
      • Ex.) average height has increased 10cm in the United States and Europe since 1800’s
  • Polygenic Traits
    • Traits coded for by many genes
    • Ex.) skin color, hair color
  • The Human Genome
    • Our complete set of genetic information
    • Includes tens of thousands of genes
    • Until recently the identification of a human gene took years of work
    • Long generation times
    • Complex life cycle
    • Produce few offspring
    Humans aren’t easy test subjects
  • Blood Group Genes
    • A number of genes are responsible for human blood groups, but the best known are the ABO and Rh blood groups
    • Rh blood groups
    • Rh+ (dominant)
    • Rh- (recessive)
  • Q: How do scientists identify recessive alleles that cause these disorders
    • A: Compare affected persons genotype to normal persons
  • PKU – phenylketonuria
    • Lack enzyme needed to break down phenylalanine
    • Found in milk and other foods
    • If newborn has PKU, phenylalanine may build up in the tissues during severe mental retardation
    • If newborns are tested early, they can be placed on a low phenylalanine diet which prevents most of the affects
    • PKU is caused by a recessive allele carried on chromosome 12
  • PKU
  • Tay Sachs
    • Autosomal recessive
    • Found mostly in Jewish families of central and eastern European ancestry
    • Results in nervous system breakdown and death in the first few years of life
    • There is no treatment, but there is a test prospective parents can take
  • Achondroplasia - dwarfism
    • Never reach 4 feet 4 inches
    • Cartilage forms in such a way that the arms and legs end up being disproportionately short
    • 1 in every 10,000 is affected
  • Huntington's
    • Progressive loss of muscle control and mental function until death occurs
    • People with disease show no symptoms until they are in their 30’s and 40’s
  • Huntington's affect on the brain
  • Codominant
    • Sickle cell disease
    • Affects 1 in 500 African Americans
  • From Gene to Molecule
  • Cystic Fibrosis (CF)
    • Most common among people whose ancestors come from northern Europe
    • Caused by a recessive allele on chromosome 7
    • Produce a thick heavy mucus that clogs their lungs and breathing passageways
    • Serious digestive problems
    • Only half survive into their 20’s
  • Sickle Cell Disease
    • Characterized by the bent and twisted shape of the red blood cell
    • Sickle shaped red blood cell tend to get stuck in the capillaries
    • Produce physical weakness and damage to the brain, heart and spleen
    • Sometimes fatal
    • Change in just one DNA base
    • This change inserts amino acid valine in place of glutamic acid
    • Hemoglobin molecules stick together and form long chains that produce the characteristic shape of sickled cells
  • Q: Why do so many African Americans carry the sickle cell allele?
    • A: Many African Americans have West Central African ancestry where malaria is a serious problem
    • People who are heterozygous for the sickle cell allele don’t get sickle cell and they don’t get malaria
  • Where malaria is common Where sickle cell is common
  • Dominant or Recessive
    • It all depends on the nature of a genes protein product and its role in the cell
    • Ex.) In CF, one copy of the normal allele can supply cells with enough chloride channel proteins to function therefore the normal CF allele is considered ____________________
  • 14-2 Human Chromosomes
    • A human diploid cell contains more than 6 billion nucleiotide pairs of DNA
    • Despite its size, all of this information is neatly packed into the 46 chromosomes present in every diploid cell
    • Each chromosome is like a library containing hundreds or even thousands of books
    • Biologists are many decades away from mastering the contents of these books, but they are learning just how many books there are and what they deal with
  • Sex Linked Genes
    • Genes located on the sex chromosomes
    • Most found on the ________ chromosome
  • Colorblindness
    • Gene associated with color vision are located on the X chromosome
    • Affects 1 in 10 males
    • Affects 1 in 100 females
  • Q: Why the difference between the sexes?
    • A: Males have ____________________________ X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive
    • In order for a woman to be affected, there must be __________________________ of the allele
    just one Two copies
  • Hemophilia
    • A protein necessary for normal ______________________________is missing
    • 1 in 10,000 males
    • People with hemophilia can bleed to death from minor cuts and may suffer from internal bleeding
    • Treated with normal clotting factors
    Blood clotting
  • Duchenne Muscular Dystrophy
    • Results in progressive weakening and loss of skeletal muscle
    • Rarely live past early adulthood
    • In the U.S. 1 in 3000 males is born with Duchenne muscular dystrophy
    • Caused by a defective version of the gene that codes for a muscle protein
  • X-Chromosome Inactivation
    • Q: If all you need is one X chromosome, what happens to the extra X chromosome in females?
    • A: one chromosome is randomly switched off
    • Forms a barr body – dense region in the nucleus
  • Calico Cats
    • Fur color is on the X chromosome. Some areas have one color switched on, and others its switched off
  • nondisjunction
    • When homologous chromosomes fail to separate – most common error in meiosis
    • If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes
  • Down Syndrome
    • When nondisjunction happens and a baby is born with 3 copies of chromosome 21
    • Trisomy 21
    • 1 in 800 in U.S.
    • Mild to severe retardation
    • Susceptible to many diseases
    • Increased frequency of birth defects
  • Down Syndrome
  • Turners Syndrome (female)
    • Only inherit one X chromosome, and no Y
    • Genotype = XO
    • Women with Turner syndrome are sterile, their sex organs don’t properly develop at puberty
  • Klinefelters Syndrome (males)
    • Inherit extra X chromosomes
    • Genotype = XXY
    • The extra X interferes with meiosis and usually prevents them from reproducing
    • Some cases XXXY or XXXXY
    • These abnormalities show us the role of Y in sex determination
      • Even in combination with several X’s, the Y makes them male
    • But if this Y is absent, the embryo develops into a female
  • 14-3 Human Molecular Genetics
  • Human DNA Analysis
    • Way too much DNA to search through
    • Biologists search the volumes of the human genome using DNA sequences
  • Testing for alleles
    • If two prospective parents suspect they might be carrying recessive alleles for a genetic disorder they can now get a test to determine the risk of passing that trait on to their children
      • Use labeled DNA probes to detect specific sequences found in disease causing alleles
      • Looking at changes in restrictive enzyme cutting sites
      • Looking at differences in lengths of alleles
  • DNA fingerprinting
    • Analyzes sections of DNA that have little or no known function but vary widely from one individual to another
    • Used to settle paternity disputes
    • Convict criminals and overturn convictions
  • The Human Genome Project
    • Advances in DNA sequencing technologies at the close of the twentieth century made it possible to begin sequencing entire genomes
    • At first, biologists worked on small genomes of viruses and bacteria
    • In 1990, scientists in the United States and other countries began the Human Genome Project
      • An attempt to sequence all human DNA
    • In 2000 scientists announced that the DNA sequence of the human genome was essentially complete
    • We estimate as little as 31,000 genes
      • Fruit fly – 14,000
      • C. elegans worm 20,000
    • Now the task is to figure out how so few genes make an organism as complex as us
  • Promoter
    • Section of DNA that signals the start of a gene
    • Researchers are looking for genes that provide useful clues to some of the basic properties of life
    • Also looking for genetic information that may be useful in developing new drugs and treatment of disease
  • A Breakthrough for Everyone
    • Data from the human genome project is posted on the internet on a daily basis
  • Gene Therapy
    • Replacing an absent or faulty gene by a normal working gene
  • Ethical Issues in Human Genetics
    • There are many questions which science will rapidly force society to come to grips with
    • If it’s just as easy to manipulate genes for personal preference then it is to cure a disease should we do it?
    • Our society will have to develop a thoughtful and ethical conscious of what should and shouldn’t be done with the human genome