Mendelian Genetics PowerPoint


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Mendelian Genetics PowerPoint

  1. 1. Mendelian Genetics Bio 156 Human Biology for Allied Health Pima CC East Fall 2006
  2. 2. Gregor Mendel <ul><li>In 1865, Mendel published the paper &quot;Experiments in Plant Hybridization&quot; </li></ul><ul><li>studied seven basic characteristics of the pea pod plants </li></ul><ul><li>Developed Mendel’s Laws </li></ul>1882
  3. 4. Mendel’s laws <ul><li>The sex cell of a plant or animal can only contain one factor (allele) for a specific trait </li></ul><ul><li>Characteristics are inherited independently from other characteristics </li></ul><ul><li>Each inherited characteristic is determined by two heredity factors/genes, </li></ul><ul><ul><li>one from each parent </li></ul></ul><ul><ul><li>determines whether a gene will be dominant or recessive. </li></ul></ul>
  4. 5. Chromosomes <ul><li>Normal Human cells have 46 chromosomes </li></ul><ul><ul><li>23 homologous chromosome pairs </li></ul></ul><ul><ul><ul><li>22 Pair are Autosomes </li></ul></ul></ul><ul><ul><ul><ul><li>Look similar </li></ul></ul></ul></ul><ul><ul><ul><li>1 pair are Sex Chromosomes </li></ul></ul></ul><ul><ul><ul><ul><li>X and Y </li></ul></ul></ul></ul><ul><ul><li>Females have 2 X chromosomes (XX) </li></ul></ul><ul><ul><li>Males have one X and one Y (XY) </li></ul></ul>
  5. 6. How Many Chromosomes??? <ul><li>Pea Plant =14 </li></ul><ul><li>Cat = 38 </li></ul><ul><li>Dog = 78 </li></ul><ul><li>Ichthyomys pittieri (semiaquatic rodent)= 94 [highest for a mammal] </li></ul><ul><li>Ophioglossum reticulatum (fern) =1200 or 1260 [highest plant] </li></ul><ul><li>Aulacantha (protozoa) = 1600 </li></ul>(Diploid number)
  6. 7. Parental Chromosomes <ul><li>23 chromosomes inherited from mother (ovum) </li></ul><ul><ul><li>22 autosomes & one sex chromosome (X) </li></ul></ul><ul><li>23 chromosomes inherited from father (sperm) </li></ul><ul><ul><li>22 autosomes & one sex chromosome (X or Y) </li></ul></ul><ul><li>Sperm and egg cells each contain 23 haploid chromosomes </li></ul><ul><ul><li>paternal chromosomes combine with maternal chromosomes </li></ul></ul>
  7. 8. Chromosomes <ul><li>The 46 human chromosomes </li></ul><ul><ul><li>22 pairs of autosomal chromosomes </li></ul></ul><ul><ul><li>2 sex chromosomes </li></ul></ul><ul><li>almost 3 billion base pairs of DNA </li></ul><ul><li>Chromosomes range in length from about 50 million to 250 million base pairs </li></ul><ul><li>The human genome has an estimated 20,000 to 25,000 genes. </li></ul>
  8. 9. Chromosome 1 <ul><li>Chromosome 1 contains nearly twice as many genes as the average chromosome and makes up eight percent of the human genetic code. </li></ul><ul><li>It is packed with 3,141 genes and linked to 350 illnesses including cancer, Alzheimer's and Parkinson's disease </li></ul><ul><li>The sequence of chromosome 1, which is published online by the journal Nature, took a team of 150 British and American scientists 10 years to complete. </li></ul>
  9. 10. Chromosome 1& Human Genome <ul><li>The sequencing of chromosome 1 has led to the identification of more than 1,000 new genes. </li></ul><ul><li>The scientists also identified 4,500 new SNPs -- single nucleotide polymorphisms -- which are the variations in human DNA that make people unique. </li></ul>
  10. 11. Human Traits <ul><li>Researchers have identified over 15,000 genetically inherited human traits.  </li></ul><ul><li>More than 5,000 of them are diseases or other abnormalities.  </li></ul>
  11. 12. Chromosomes and Heredity <ul><li>Heredity = transmission of genetic characteristics from parent to offspring </li></ul><ul><li>Karyotype = chart of chromosomes at metaphase </li></ul><ul><ul><li>Chromosomes are arranged in order by size and structure </li></ul></ul>
  12. 13. Karyotype Procedure <ul><li>involves blocking cells in mitosis </li></ul><ul><li>staining the condensed chromosomes with Giemsa dye. </li></ul><ul><ul><li>The dye stains regions of chromosomes that are rich in the base pairs Adenine (A) and Thymine (T) producing a dark band. </li></ul></ul><ul><li>A common misconception is that bands represent single genes, but in fact the thinnest bands contain over a million base pairs and potentially hundreds of genes </li></ul>
  13. 14. SEM of Chromosomes
  14. 15. Normal Human Male Karyotype
  15. 16. Genes and Alleles <ul><li>Each chromosome carries multiple genes </li></ul><ul><li>Locus (pl. Loci) </li></ul><ul><ul><li>location of a gene on chromosome </li></ul></ul><ul><li>Alleles </li></ul><ul><ul><li>different forms of gene </li></ul></ul><ul><ul><ul><li>Produce alternate forms of the same trait </li></ul></ul></ul><ul><ul><li>at same locus on the 2 homologous chromosomes </li></ul></ul>
  16. 17. Genes and Alleles <ul><li>Dominant allele </li></ul><ul><ul><li>produces protein responsible for visible trait </li></ul></ul><ul><ul><ul><li>If dominant allele present  gene expressed </li></ul></ul></ul><ul><ul><ul><li>Often written as Upper Case letter (ie. D) </li></ul></ul></ul><ul><li>Recessive allele </li></ul><ul><ul><li>Only expressed when no dominant allele is present </li></ul></ul><ul><ul><ul><li>e.g. when both alleles are recessive </li></ul></ul></ul><ul><ul><ul><li>Often written as corresponding lower case letter (ie.d) </li></ul></ul></ul>
  17. 18. Genes and Alleles <ul><li>Homozygous </li></ul><ul><ul><li>Both homologous chromosomes have same allele for the gene (trait) </li></ul></ul><ul><ul><ul><li>Both Dominant: DD </li></ul></ul></ul><ul><ul><ul><li>Both Recessive: dd </li></ul></ul></ul><ul><li>Heterozygous </li></ul><ul><ul><li>Homologous chromosomes have different alleles for the a gene </li></ul></ul><ul><ul><ul><li>One Dominant & one recessive: Dd </li></ul></ul></ul>
  18. 19. Genes and Alleles <ul><li>Genotype </li></ul><ul><ul><li>The alleles an individual has for a particular trait </li></ul></ul><ul><ul><ul><li>DD or Dd or dd </li></ul></ul></ul><ul><li>Phenotype </li></ul><ul><ul><li>The physical expression of the alleles for a particular trait </li></ul></ul><ul><ul><ul><li>What you see… </li></ul></ul></ul>
  19. 20. Genetics of Earlobes
  20. 21. How to complete a Punnet Square <ul><li>Determine Genotype of each parent </li></ul><ul><ul><li>AA or Aa or aa </li></ul></ul><ul><li>Write Down the cross </li></ul><ul><ul><li>AA x aa </li></ul></ul><ul><li>Draw a Punnet Square </li></ul>
  21. 22. How to complete a Punnet Square AA x aa <ul><li>Split the letters of each parent genotype and put them outside the Punnet Square </li></ul>a a A A
  22. 23. How to complete a Punnet Square <ul><li>Determine the offspring by Filling in Punnet square </li></ul>a a A A A A
  23. 24. How to complete a Punnet Square <ul><li>Determine the offspring by Filling in Punnet square </li></ul>a a A A A A A A
  24. 25. How to complete a Punnet Square <ul><li>Determine the offspring by Filling in Punnet square </li></ul>a a A A A A Aa Aa
  25. 26. How to complete a Punnet Square <ul><li>Determine the offspring by Filling in Punnet square </li></ul>a a A A Aa Aa Aa Aa
  26. 27. How to complete a Punnet Square <ul><li>Determine the offspring by Filling in Punnet square </li></ul>Parents AA x aa Offspring 100% Aa Results a a A A Aa Aa Aa Aa
  27. 28. Genetics of Earlobes
  28. 29. Genetics of Earlobes Punnett square
  29. 30. Parents Dd x Dd D D d D D d
  30. 31. Parents Dd x Dd D D d d d D D d
  31. 32. Parents Dd x Dd D D d d D D d D D d
  32. 33. Parents Dd x Dd D D d d D D d d d D D d
  33. 34. Dd Heterozygous, detached earlobe DD Homozygous, detached earlobe Dd Heterozygous, detached earlobe dd Homozygous, attached earlobe Parents Dd x Dd Genotype 25% DD 50% Dd 25% dd Phenotype 75% det 25% att d D D d
  34. 35. Sex-Linked Inheritance <ul><li>Sex Linked Traits – Genes that are carried by either sex chromosome </li></ul><ul><ul><li>X chromosome contains about 1000 human X-linked genes </li></ul></ul><ul><ul><li>Smaller Y Chromosome only ~ 78 genes </li></ul></ul><ul><li>Men only have one X chromosome </li></ul><ul><ul><li>No corresponding gene on Y so gene on X expressed (even if recessive) </li></ul></ul>
  35. 36. Sex-Linked Inheritance <ul><li>Recessive allele on X, no gene locus for trait on Y </li></ul><ul><li>so hemophilia more common in men </li></ul><ul><ul><li>(mother must be carrier) </li></ul></ul>
  36. 37. Hemizygous <ul><li>An individual who has only one member of a chromosome pair or chromosome segment rather than the usual two </li></ul><ul><li>X-linked genes in males who under usual circumstances have only one X chromosome </li></ul>
  37. 40. Gene Pool <ul><li>Gene pool </li></ul><ul><ul><li>collective genetic makeup of whole population </li></ul></ul><ul><ul><li>the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. </li></ul></ul>
  38. 41. Alleles at the Population Level <ul><li>Dominance and recessiveness of allele do not determine frequency in a population </li></ul><ul><li>Some recessive alleles are the most common </li></ul><ul><ul><li>blood type O </li></ul></ul><ul><li>Some dominant alleles are rare </li></ul><ul><ul><li>polydactyly and blood type AB, </li></ul></ul>
  39. 42. ABO grouping Percentages* *In US population AB- 1% AB+ 3% B- 2% B+ 9% A- 6% A+ 34% O- 7% O + 38%
  40. 43. Percentage of each ABO Blood Type by Country 12 10 4 3 4 AB 26 22 10 8 10 B 27 38 45 42 40 A 35 30 41 47 46 O % % % % % ABO Type China Japan Germany G.B. U.S. Country
  41. 44. Some exceptions to Simple Mendelian Genetics (we will only discuss a few…)
  42. 45. Multiple Alleles <ul><li>Multiple alleles </li></ul><ul><ul><li>more than 2 alleles for a trait </li></ul></ul><ul><li>ABO blood type system </li></ul><ul><ul><li>three alleles (A, B, and O) </li></ul></ul><ul><ul><ul><li>each individual only inherits two of them </li></ul></ul></ul><ul><ul><ul><li>one from each parent </li></ul></ul></ul>
  43. 46. Multiple Alleles <ul><li>human Human Leukocyte Antigen (HLA) system </li></ul><ul><ul><li>responsible for identifying and rejecting foreign tissue in our bodies </li></ul></ul><ul><ul><li>can have at least 30,000,000 different genotypes.  </li></ul></ul><ul><li>It is the HLA system which causes the rejection of organ transplants. </li></ul>
  44. 47. Codominance <ul><li>Codominant Allele </li></ul><ul><ul><li>both alleles expressed, I A I B = type AB blood </li></ul></ul>
  45. 48. Incomplete Dominance <ul><li>Incomplete dominance </li></ul><ul><ul><li>phenotype intermediate between traits for each allele </li></ul></ul>
  46. 49. Polygenic Inheritance <ul><li>Polygenic Inheritance </li></ul><ul><ul><li>2 or more genes combine their effects to produce single phenotypic trait </li></ul></ul><ul><ul><ul><li>skin and eye color, alcoholism and heart disease </li></ul></ul></ul>
  47. 50. Pleiotropy <ul><li>Single gene causes multiple phenotypic traits (ex. sickle-cell disease) </li></ul><ul><ul><li>sticky, fragile, abnormal shaped red blood cells at low oxygen levels cause anemia and enlarged spleen </li></ul></ul>
  48. 51. Penetrance and Environmental Effects <ul><li>Penetrance </li></ul><ul><ul><li>% of population to express predicted phenotype given their genotypes </li></ul></ul><ul><li>Role of environment </li></ul><ul><ul><li>brown eye color requires phenylalanine from diet to produce melanin, the eye pigment </li></ul></ul>
  49. 52. Eye Color… <ul><li>Eye color comes from a combination of two black and yellow pigments called melanin in the iris of your eye </li></ul><ul><li>no melanin in the front part of your iris, you have blue eyes. </li></ul><ul><li>An increasing proportion of the yellow melanin, in combination with the black melanin, results in shades of colors between brown and blue, including green and hazel. </li></ul>
  50. 53. Eye Color… <ul><li>Three gene pairs controlling human eye color are known. </li></ul><ul><li>Two of the gene pairs occur on chromosome pair 15 </li></ul><ul><ul><li>The bey 2 gene ( EYCL3 ), </li></ul></ul><ul><ul><ul><li>has a brown and a blue allele </li></ul></ul></ul><ul><ul><li>The bey 1 </li></ul></ul><ul><ul><ul><li>is a central brown eye color gene </li></ul></ul></ul><ul><li>One occurs on chromosome pair 19. </li></ul><ul><ul><li>The gey gene ( EYCL1 ) </li></ul></ul><ul><ul><ul><li>has a green and a blue allele.. </li></ul></ul></ul>
  51. 54. Modeling Eye Color… <ul><li>The bey 2 gene ( EYCL3 ), </li></ul><ul><ul><ul><li>brown allele Dominant </li></ul></ul></ul><ul><ul><ul><li>blue allele recessive </li></ul></ul></ul><ul><li>The gey gene ( EYCL1 ) </li></ul><ul><ul><ul><li>Green allele Dominant to blue BUT recessive to Brown </li></ul></ul></ul><ul><ul><ul><li>blue allele recessive </li></ul></ul></ul><ul><li>And this still doesn’t explain, hazel, grey and other colors… MORE TO DISCOVER!!! </li></ul>