Genetic traits and sex in humans


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Genetic traits and sex in humans

  1. 1. Genetic Traits and Sex in Humans 05/20/10 00:00
  2. 2. Learning Objectives <ul><li>What is a sex chromosome? </li></ul><ul><li>Understand how sex is determined and know some specific examples. </li></ul><ul><li>Be able to describe how X and Y chromosomes apply to the determination of human sexes. </li></ul><ul><li>Understand the inheritance patterns of sex-linked genetic diseases in humans . </li></ul>05/20/10 00:00
  3. 3. <ul><li>As humans, we are very accustomed to considering others as male or female, girl or boy, or man and woman. </li></ul>05/20/10 00:00
  4. 4. <ul><li>The majority of sexually reproducing organisms on earth are functionally both male and female at the same time. </li></ul>05/20/10 00:00
  5. 5. <ul><li>In species that do produce male and female individuals, sex may be determined in a number of different ways. </li></ul>05/20/10 00:00
  6. 6. Bees (Insects) <ul><li>Males are haploid; females are diploid </li></ul>05/20/10 00:00
  7. 7. <ul><li>In some cases, sex is determined by special chromosome, called a sex chromosome. </li></ul>05/20/10 00:00
  8. 8. Birds <ul><li>Males are ZZ; females are ZW </li></ul>05/20/10 00:00
  9. 9. Mammals <ul><li>Males are XY; females are XX </li></ul>05/20/10 00:00
  10. 10. Humans Follow the XY Sex Determination Scheme <ul><li>Humans have 23 pairs of chromosomes </li></ul><ul><ul><li>22 pairs of autosomes and 1 pair of sex chromosomes </li></ul></ul><ul><li>If the sperm is Y-carrying, the child will be a boy </li></ul>05/20/10 00:00
  11. 11. Sex-Linked Genetic Disorders <ul><li>Genes for non-sexual characters are also found on sex chromosomes. </li></ul><ul><li>Genes that are carried on the X or Y chromosomes are said to be “sex-linked” </li></ul>05/20/10 00:00
  12. 12. <ul><li>Sex-linked traits on the Y chromosome are only passed from father to son. </li></ul><ul><li>X-linked dominant traits work like autosomal dominant traits </li></ul><ul><li>X-linked recessive traits are more interesting genetically </li></ul>05/20/10 00:00
  13. 13. Variations in Size <ul><li>The X chromosome is much larger than the Y chromosome. </li></ul><ul><li>It contains 1000+ genes. </li></ul><ul><li>The Y chromosome is much smaller and contains about 26 genes. </li></ul>05/20/10 00:00
  14. 14. X-Linked Recessive Traits <ul><li>The X Chromosome of a male can display a recessive trait because the Y chromosome has no corresponding gene. </li></ul><ul><li>Such disorders are called “sex-linked” recessive </li></ul>05/20/10 00:00
  15. 15. Examples of X-Linked Recessive Traits <ul><li>Colorblindness </li></ul><ul><li>Hemophilia </li></ul><ul><li>Duchenne’s Muscular Dystrophy </li></ul>05/20/10 00:00
  16. 16. Colorblindness <ul><li>Most types are caused by a gene located on the X chromosome </li></ul><ul><li>Red green colorblindness is the most common type </li></ul><ul><ul><li>Amongst Caucasians; </li></ul></ul><ul><ul><ul><li>8% of males are colorblind </li></ul></ul></ul><ul><ul><ul><li>1% of females are colorblind </li></ul></ul></ul>05/20/10 00:00
  17. 17. Test For Colorblindness <ul><li>Ishihara Test </li></ul><ul><li>Normal color vision see an “8” </li></ul><ul><li>Colorblind people don’t see anything </li></ul>05/20/10 00:00
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  24. 24. Sex-linked Genetics <ul><li>We use an “X” to identify that this characteristic is carried on the X chromosome and a superscript “C” for the dominant (normal) trait or lowercase “c” for the colorblind trait. </li></ul><ul><li>X C = normal vision allele </li></ul><ul><li>X c = colorblind allele </li></ul><ul><li>Y = normal male chromosome (no allele for colorblindness) </li></ul>05/20/10 00:00
  25. 25. Example #1 <ul><li>Show a cross between a normal vision woman and a colorblind man </li></ul><ul><li>X C X C X c Y </li></ul><ul><li>X C X c Y </li></ul><ul><li>X C X c X C Y </li></ul>05/20/10 00:00
  26. 26. Example #2 <ul><li>X C X c X C Y </li></ul><ul><li>X C X c X C Y </li></ul><ul><li>X C X C X c Y </li></ul><ul><li>X C Y X c Y </li></ul><ul><li>Show a cross between a carrier woman and a normal vision man </li></ul>05/20/10 00:00
  27. 27. Hemophilia <ul><li>Aka “bleeder’s disease” </li></ul><ul><li>Much rarer than colorblindness </li></ul><ul><ul><li>1 in 10,000 males </li></ul></ul><ul><ul><li>1 in 100,000,000 females </li></ul></ul><ul><li>A protein antihemophilic factor (AHF) is missing </li></ul>05/20/10 00:00
  28. 28. Queen Victoria <ul><li>Acquired hemophilia through a mutation </li></ul><ul><ul><li>Parents didn’t have it or pass it on </li></ul></ul><ul><li>Passed it to 1 son and at least two daughters </li></ul><ul><li>The daughters were married to nobility in France and Germany and it caused the loss of at least one heir to the throne! </li></ul>05/20/10 00:00
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  30. 30. Duchenne’s Muscular Dystrophy <ul><li>Progressive wasting of skeletal muscle </li></ul><ul><li>Seldom survive past early adulthood </li></ul>05/20/10 00:00
  31. 31. Sex-Influenced Traits <ul><li>“ a trait that is NOT located on the sex chromosomes but is influenced by gender” </li></ul>05/20/10 00:00
  32. 32. Male Pattern Baldness <ul><li>All homozygous dominant show the disease (male and female) </li></ul><ul><li>No homozygous recessive show the disease (male OR female) </li></ul><ul><li>But if heterozygous, only males show the disease </li></ul>05/20/10 00:00