Human genetics


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Human genetics

  1. 1. The Human GenomeFrom Peas and fruit flies to humans…
  2. 2. What is a genome???• All the genetic information (genes) that make up an organism
  3. 3. 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)
  4. 4. 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
  5. 5. Disorders can be recessive or dominant
  6. 6. 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
  7. 7. 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
  8. 8. 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
  9. 9. 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
  10. 10. 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
  11. 11. 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
  12. 12. 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
  13. 13. 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
  14. 14. • 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
  15. 15. 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
  16. 16. 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
  17. 17. 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
  18. 18. 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
  19. 19. Turner’s Syndrome
  20. 20. • 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