Mendelian Genetics PowerPoint

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