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Human genetics

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  • 1. The Human Genome
    From Peas and fruit flies to humans…
  • 2.
  • 3. What is a genome???
    All the genetic information (genes) that make up an organism
  • 4. What makes us human?
    Analyze human chromosome…
    Karotype
    Picture of all the chromosomes in an organism
    Autosomes
    CHROMOSOMES 1-44 (pairs 1-22)
    Autosomal chromsomes
    Sex chromosomes
    Determine a person’s sex (male XY or female XX)
    Chromosome 45 and 46 (set 23)
  • 5.
  • 6. Pedigree Charts
    Shows relationships within a family
    Genetic counselors use these to infer the genotypes of family members
    Look at each generation different symbols used
  • 7.
  • 8. Disorders can be recessive or dominant
  • 9.
  • 10. Recessive disorders
    Disorder phenylketonuria (PKU)
    Caused by an autosomal recessive allele on chromosome 12
    People with this disorder lack the enzyme to break down phenylalanine (amino acid found in milk and many other foods)
    In newborns, this causes a build up of phenylalanine in tissues during the first few years of life and lead to mental retardation
    Newborns are commonly tested for PKU and then put on a low phenylalanine diet if they have the disorder
  • 11. Autosomal Recessive Allele
    Tay-Sachs Disease
    Recessive allele in Jewish families of central and eastern Europe ancestry
    Lack the enzyme to break down lipids in neural cells
    Lipid accumulation in brain cells
    Leads to nervous system break-down and death in the first few years of life
  • 12. Autosomal Recessive Disorders
    Cystic Fibrosis
    Do not have the gene that regulates mucus production
    Excess mucus in lungs, digestive tract, and liver
    Increased susceptibility to disorders
    Lung transplants usually needed after childhood
  • 13. Autosomal Dominant Disorders
    You will express disorder if you are homozygous or heterozygous dominant for that trait
    You also have higher chances of passing onto your children
    Dwarfism (achondroplasia)
    Huntington’s Disease
    Nervous system disorder
  • 14. Co-Dominant Alleles Disorders
    Sickle cell anemia
    1/500 African Americans have the disorder
    Co-dominant allele
    Causes blockages in blood vessels, preventing oxygen from getting to other cells and tissues
    Beneficial in central and east Africa because it helped destroy malaria
    If you had SCA, your body would destroy the sickle cells to protect itself and in the process, destroy the malaria parasite as well
  • 15.
  • 16. Sex-Linked Disorders
    Many sex-linked genes are found on x-chromosome
    Many genetic disorders are sex-linked
    Males have just ONE x chromosome, so whatever the X chromosome is carrying (dominant or recessive) will be expressed
    Fathers can pass it to their daughters and the disorder can show up in the daughters sons
  • 17. Sex-linked Disorders
    Red-green Color-blindness
    1/10 men
    1/100 women
    Hemophilia
    Two important genes on x-chr control blood clotting
    Person with disorder can die from minor cuts
    Recessive allele in either gene can cause it
    Duchenne Muscular Dystrophy
    Caused by defective version of a gene for a muscle protein
    Progressive weakening and loss of skeletal muscle1/3000 males
  • 18. X-chromosome Inactivation
    Females have XX and males have XY…is the second X chr in females needed??
    British Geneticist Mary Lyon
    In female cells, one x-chromosome is randomly shut off…this “shut off” chromosome is called a Barr Body
    Different X-chrm are switched off in different cells
    Generally not found in males b/c X-chrm needs to be ACTIVE
    Occurs in other mammals as well
  • 19. Barr bodies in cats
    Gene that controls color of coat spots is located on the X-chrm
    In a female, one X-chrm may have the allele for orange spots and the other X-chrm may have the allele for black spots
    Different cells in different parts of the cat’s body are switched off= different colored spots on different parts of the cat…mix or orange and black spots
    Males only have ONE active X-chrm…therefore, will they have different colored spots?
    No…only psots of ONE color (b/c on ONE active X)
    This is one way to determine the sex of a cat…cat with black AND orange spots is almost always certainly female
  • 20.
  • 21. Chromosomal Disorders
    Mechanics of meiosis (where we separate chromosomes) is usually pretty good
    But nobody’s perfect…mistakes happen….
    Most common problem…
    Nondisjunction: when homologous chromosomes fail to separate properly
    Literally means “not coming apart”
    If this occurs, ABNORMAL #s of chromosomes may find their way into gametes and a disorder of chromosome number may result
  • 22. Nondisjunction
    If one of the gametes with an ABNORMAL # ends up getting fertilized, MAJOR problems!!!
    Trisomy: “three bodies”
    Occurs when an autosomal chromosome fails to separate during meiosis
    When do chrm separate?
    Anaphase I and Anaphase 2
    One gamete ends up with an extra copy of a chromosome and then the fertilized zygote ends up with 3 copies of a chrm instead of 2
    Example: Downs Syndrome
  • 23.
  • 24.
  • 25. Down Syndrome
    Extra copy of chromosome 21
    1/800 baby’s are born with this disorder
    Produces mild to severe retardation
    Increased susceptibility to diseases, slower development, and higher frequency of birth defects
    How can one little extra copy cause so many problems?
    Scientists are still trying to figure that out…now that they have used gene mapping and identified all the genes on chromosome 21, they can begin experimenting on this problem
  • 26. Sex Chromosome Disorders
    What happens if nondisjunction happens to the sex chromosomes???
    We know we need at least one X chromosome….
    No embryos have been found with just a Y chromosome so we now X chrm contains vital genes!
    Turners Syndrome
    Females receive only one X chromosome
    Karotype 45, X
    Unable to reproduce, sex organs do not develop at puberty
    Klinefelters Syndrome
    Males receive an extra X chromosome
    Karotype 47, XXY
    Prevents individuals from reproducing
    Cases of individuals with XXXY and XXXXY
    Y chromosome contains “sex determining region” SDR, which gives male characteristics and development
    If region is absent, embryo develops into female
  • 27. Turner’s Syndrome
  • 28.
  • 29. What about an extra Y?
    Males with 47, XYY produce more male hormones and express a more expressive behavior
    More testosterone=more aggressive behavior
    Higher number of men in prison for violent crimes have XYY however there is a large population of men with XYY that do not exhibit (or at least act upon) this aggression
    Cannot use this as an excuse for aggressive behavior or else criminals would be pleading an extra Y instead of insanity :-o