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Introduction to DNA and Genetics


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Introduction to DNA and Genetics

  1. 1. Genes Introduction to Genetics
  2. 2. What is DNA? <ul><li>DNA stands for D eoxyribo N ucleic A cid </li></ul><ul><li>It is the hereditary material in humans and almost all other organisms. </li></ul><ul><li>Most DNA is located in the cell nucleus. </li></ul><ul><li>“ Blueprint of life” </li></ul><ul><li>The main role of DNA molecules is the long-term storage of information . </li></ul>
  3. 3. DNA Structure <ul><li>DNA is a double-stranded molecule . </li></ul><ul><li>The shape of the DNA molecule is a double-helix (think of a spiral staircase or like a twisted ladder). </li></ul><ul><li>The sides of the ladder are composed of alternating sugars (deoxyribose) and phosphates. </li></ul><ul><li>The rungs of the ladder are composed of nucleotides. </li></ul>
  4. 4. <ul><li>The structuof DNA was established by James Watson and Francis Crick. </li></ul>DNA Structure
  5. 5. Base Pairing Rule Nucleotides (also called Bases) Adenine, Thymine, , Guanine, Cytosine or A, T, G, C Nucleotides pair in a specific way - called the Base-Pair Rule Adenine pairs to Thymine A T Guanine pairs to Cytosin e G C Memory helper - Think &quot;A T Granite City&quot; - which is where you live.
  6. 6. What is a gene? <ul><li>Gene - a segment of DNA that codes for a protein, which in turn codes for a trait (skin tone, eye color.etc), </li></ul><ul><li>a gene is a stretch of DNA. </li></ul><ul><li>Every person has two copies of each gene, one inherited from each parent. </li></ul>
  7. 7. What is a chromosome? <ul><li>Chromosomes are DNA molecule packaged into thread-like structures in the nucleus </li></ul>
  8. 8. How many chromosomes do people have? <ul><li>In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. </li></ul><ul><li>Diploid a cell that contains “two sets” of chromosome 2N </li></ul><ul><li>Haploid a cell that contains “one set” of chromosome </li></ul>
  9. 9. Sex Determination <ul><li>Sex cell chromosomes determine the sex of an organism </li></ul><ul><li>Sex cells are the sperm and egg–gametes </li></ul><ul><li>Females have two X chromosomes, (XX) </li></ul><ul><li>Males have one X and one Y chromosome (XY) </li></ul><ul><li>Zygote is the union of the sperm and egg (46 chromosomes). </li></ul>
  10. 10. <ul><li>Heredity is the transmission of characteristics from parents to offspring. </li></ul><ul><li>The genes for many traits are passed down in families from parents to children. </li></ul><ul><li>Because you come from two parents, each parent will provide one half of your genes for any trait. That is called an &quot;allele.&quot; So you have two alleles for each gene, one from each parent. </li></ul>
  11. 11. Gregor Mendel
  12. 12. Gregor Mendel <ul><li>“ Father” of genetics </li></ul><ul><li>Austrian monk, mid-1800s </li></ul><ul><li>Researched pea plant inheritance </li></ul><ul><ul><li>Easy to grow, fast reproduction </li></ul></ul><ul><ul><li>Studied plant height, pea shape/color, pod color, etc. </li></ul></ul>
  13. 14. Pea Plant Reproduction <ul><li>Self-pollination </li></ul><ul><ul><li>Male gametes (pollen) fertilize egg of same flower </li></ul></ul><ul><ul><li>Produces pure-bred offspring </li></ul></ul><ul><ul><li>True-breeding: produce offspring identical to parent when self-pollinated </li></ul></ul>
  14. 15. Pea Plant Reproduction <ul><li>Cross-pollination </li></ul><ul><ul><li>Pollen from one plant fertilizes egg of another plant </li></ul></ul><ul><ul><li>Offspring have two parents </li></ul></ul>
  15. 16. Mendel’s Experiments <ul><li>P = Parent generation </li></ul><ul><li>F 1 = First filial generation </li></ul><ul><li>F 2 = Second filial generation (F 1 X F 1 ) </li></ul><ul><ul><ul><ul><li>Outcome </li></ul></ul></ul></ul><ul><li>P Pure Green X Pure Yellow </li></ul><ul><li>F 1 All Green </li></ul><ul><li>F 2 3 Green:1 Yellow </li></ul>
  16. 18. Mendel’s Conclusions <ul><li>Law of Dominance – one allele (form of a gene) is dominant, one is recessive </li></ul><ul><ul><li>Recessive trait was hidden in F 1 generation </li></ul></ul><ul><ul><li>Green = dominant </li></ul></ul><ul><ul><li>Yellow = recessive </li></ul></ul>
  17. 19. Mendel’s Conclusions <ul><li>Law of Segregation: alleles for a gene separate when gametes form (meiosis I) </li></ul><ul><ul><li>Each gamete gets one copy of each gene </li></ul></ul>
  18. 20. Some Vocab. <ul><li>Genotype – allele combination </li></ul><ul><li>Genotype is the genetic make up </li></ul><ul><ul><li>Capital letter = dominant allele </li></ul></ul><ul><ul><li>Lowercase letter = recessive allele </li></ul></ul><ul><ul><li>Ex – AA, Aa, aa </li></ul></ul><ul><li>Phenotype – physical appearance </li></ul><ul><ul><li>Ex – green, yellow </li></ul></ul>
  19. 21. Some Vocab. <ul><li>Homozygous – two alleles Same </li></ul><ul><li>Homozygous organisms that have two identical alleles. </li></ul><ul><ul><li>Homozygous dominant: AA </li></ul></ul><ul><ul><li>Homozygous recessive: aa </li></ul></ul><ul><li>Heterozygous – two alleles different </li></ul><ul><li>Heterozygous organism with two different alleles. </li></ul><ul><ul><li>Aa </li></ul></ul>
  20. 22. Dominant and recessive <ul><li>Dominant traits are the expressed characteristic. It is always represented with a capital letter </li></ul><ul><li>Recessive traits are the repressed alleles; the ones that are not expressed. It is always represented with a lower case </li></ul>
  21. 23. Probability <ul><li>Punnett squares are used to predict the probability of certain traits in offspring of genetic crosses </li></ul><ul><li>Tt X Tt </li></ul><ul><ul><li>½ chance of getting ‘t’ from mom, ½ chance of getting ‘t’ from dad </li></ul></ul><ul><ul><li>½ X ½ = ¼ tt in offspring </li></ul></ul>
  22. 24. Punnett Squares <ul><li>First must determine possible gametes </li></ul><ul><li>Heterozygous tall plant = Tt </li></ul><ul><ul><li>Half of gametes will get ‘T’, other half will get ‘t’ </li></ul></ul><ul><li>Homozygous tall plant = TT </li></ul><ul><ul><li>All gametes will get ‘T’ </li></ul></ul>
  23. 25. Punnett Squares <ul><li>Monohybrid cross </li></ul><ul><ul><li>Cross involving one trait </li></ul></ul><ul><li>Gametes go on the top and side </li></ul><ul><li>Combine gametes to find possible offspring </li></ul>Tt X Tt
  24. 26. Punnett Squares <ul><li>Genotype ratio </li></ul><ul><li>1TT: 2Tt: 1tt </li></ul><ul><li>Phenotype ratio </li></ul><ul><li>3 tall: 1 short </li></ul>Tt X Tt
  25. 27. Dihybrid Cross <ul><li>Mendel looked at the inheritance patterns of two traits </li></ul><ul><ul><li>Seed shape and seed color </li></ul></ul><ul><li>Found that the traits were inherited independently of each other </li></ul><ul><li>Law of Independent Assortment </li></ul><ul><ul><li>Genes on separate chromosomes are inherited at random </li></ul></ul><ul><ul><li>Due to random chromosome shuffling in Metaphase I </li></ul></ul>
  26. 28. Independent Assortment Metaphase I
  27. 30. Non-Mendelian Genetics <ul><li>Not all traits follow Mendel’s Law of Dominance </li></ul><ul><li>Four Variations </li></ul><ul><ul><li>Incomplete Dominance (blending) </li></ul></ul><ul><ul><li>Codominance (two phenotypes) </li></ul></ul><ul><ul><li>Multiple Alleles </li></ul></ul><ul><ul><li>Polygenic Traits </li></ul></ul>
  28. 31. Incomplete Dominance <ul><li>Neither allele is dominant, both produce a protein </li></ul><ul><li>Heterozygous phenotype is a blend of both homozygous phenotypes </li></ul><ul><li>Ex – wavy hair, pink flowers </li></ul>
  29. 32. Incomplete Dominance
  30. 33. Codominance <ul><li>Neither allele dominates the other, both produce a protein </li></ul><ul><li>Heterozygous phenotype is a combination of both homozygous phenotypes </li></ul><ul><li>Ex – checkered chicken, human blood types, </li></ul>
  31. 35. Multiple Alleles <ul><li>Some genes have more than two alleles </li></ul><ul><li>Each individual only gets two, but there are more than two in the population </li></ul><ul><li>Ex – Rabbit fur color </li></ul>
  32. 36. Multiple Alleles <ul><li>Rabbit fur alleles (in order of dominance) </li></ul><ul><ul><li>C: dark gray </li></ul></ul><ul><ul><li>c ch : chinchilla </li></ul></ul><ul><ul><li>c h : himalayan </li></ul></ul><ul><ul><li>c: albino </li></ul></ul>
  33. 37. Multiple Alleles
  34. 38. Polygenic Traits <ul><li>Many traits are controlled by more than one gene </li></ul><ul><li>Traits show wide variation </li></ul><ul><li>Ex – human height, IQ, bell pepper colors </li></ul>
  35. 39. Sources <ul><li> </li></ul>