Mendel and the Gene Idea
Gregor Mendel: The Man <ul><li>Austrian monk </li></ul><ul><li>Began breeding peas in 1857 to study inheritance </li></ul>...
Why Peas? <ul><li>Available in many varieties </li></ul><ul><ul><li>Flower color, seed color, flower position, pod color, ...
Mendel’s Procedure <ul><li>Crossed male pea parts (stamens) and female pea parts (carpels) with opposite traits </li></ul>...
Mendel’s Predictions <ul><li>Crossing purple and white flowers would result in an intermediate phenotype </li></ul><ul><ul...
Mendel’s Findings <ul><li>Alternative versions of genes (different alleles) account for variations in inherited characters...
Mendel’s Findings <ul><li>For each characteristic, an organism inherits two alleles, one from each parent </li></ul><ul><u...
Mendel’s Findings <ul><li>If the two alleles differ, then one, the  dominant allele , is fully expressed in the organism’s...
Mendel’s Findings <ul><li>The two alleles for each trait segregate during gamete production. </li></ul><ul><ul><li>An egg ...
Some Terminology <ul><li>Punnett Square: </li></ul><ul><ul><li>A diagram used to predict the results of a genetic cross </...
TestCross <ul><li>A testcross is used to determine the genotype of a parental organism </li></ul><ul><li>Cross the organis...
Law of Independent Assortment <ul><li>Each pair of alleles segregates into gametes independently </li></ul><ul><ul><li>Jus...
Probability <ul><li>Probability scale ranges from 0 to 1 </li></ul><ul><ul><li>If an event is certain to happen, it has a ...
The Rule of Multiplication <ul><li>To determine the chance that two or more independent events will occur together in a sp...
The Rule of Addition <ul><li>The probability of an event that can occur in two or more different ways is the sum of the se...
Incomplete Dominance <ul><li>F 1  hybrid is intermediate between the two parents </li></ul><ul><li>1:2:1 ratio </li></ul><...
Codominance <ul><li>Both alleles are separately manifested in the phenotype </li></ul><ul><ul><li>Example: Horses </li></u...
Multiple Alleles <ul><li>Genes that exist in more than two allelic forms </li></ul><ul><li>Example: ABO Blood Typing </li>...
Pleiotropy <ul><li>Def’n: </li></ul><ul><ul><li>The ability of a gene to affect an organism in many ways </li></ul></ul><u...
Epistasis <ul><li>Def’n: </li></ul><ul><ul><li>A gene at one locus (location) alters the phenotypic expression of a gene a...
Polygenic Inheritance <ul><li>Many characteristics, including human skin color and height, vary along a continuum among th...
Pedigrees <ul><li>A pedigree is a family tree that shows the interrelationships of parents and children across the generat...
Recessive Genetic Disorders <ul><li>Cystic Fibrosis (cc) </li></ul><ul><ul><li>Recessive disorder; most common in Caucasia...
Societal Factors… <ul><li>The prevalence of recessive genetic disorders greatly increases when closely-related relatives i...
Dominant Genetic Disorders <ul><li>Dwarfism: </li></ul><ul><ul><li>DD or Dd = dwarf phenotype </li></ul></ul><ul><li>Hunti...
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Mendel And The Gene Idea

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Mendel And The Gene Idea

  1. 1. Mendel and the Gene Idea
  2. 2. Gregor Mendel: The Man <ul><li>Austrian monk </li></ul><ul><li>Began breeding peas in 1857 to study inheritance </li></ul><ul><li>Kept very accurate records of his laboratory work and used very large sample sizes </li></ul>
  3. 3. Why Peas? <ul><li>Available in many varieties </li></ul><ul><ul><li>Flower color, seed color, flower position, pod color, seed shape, pod shape, stem length </li></ul></ul><ul><li>Mendel could control which plants mated with which </li></ul><ul><li>Peas grow quickly! </li></ul>
  4. 4. Mendel’s Procedure <ul><li>Crossed male pea parts (stamens) and female pea parts (carpels) with opposite traits </li></ul><ul><li>Carpel matures to first-generation offspring (F 1 ) </li></ul>
  5. 5. Mendel’s Predictions <ul><li>Crossing purple and white flowers would result in an intermediate phenotype </li></ul><ul><ul><li>Mendel thought light purple flowers would be the result! </li></ul></ul>
  6. 6. Mendel’s Findings <ul><li>Alternative versions of genes (different alleles) account for variations in inherited characters </li></ul><ul><ul><li>The gene for flower color (example) exists in two versions – purple and white </li></ul></ul><ul><ul><li>Each version is called an allele </li></ul></ul>
  7. 7. Mendel’s Findings <ul><li>For each characteristic, an organism inherits two alleles, one from each parent </li></ul><ul><ul><li>An allele is a part of a chromosome </li></ul></ul><ul><ul><li>Each parent contributes one chromosome of each homologous pair </li></ul></ul>
  8. 8. Mendel’s Findings <ul><li>If the two alleles differ, then one, the dominant allele , is fully expressed in the organism’s appearance; the other, the recessive allele , has no noticeable effect on the organism’s appearance. </li></ul>
  9. 9. Mendel’s Findings <ul><li>The two alleles for each trait segregate during gamete production. </li></ul><ul><ul><li>An egg cell or sperm cell receives only one allele </li></ul></ul><ul><ul><li>Each parent passes on only one of his/her 2 alleles </li></ul></ul><ul><ul><li>This is Mendel’s Law of Segregation </li></ul></ul>
  10. 10. Some Terminology <ul><li>Punnett Square: </li></ul><ul><ul><li>A diagram used to predict the results of a genetic cross </li></ul></ul><ul><li>Homozygous vs. Heterozygous: </li></ul><ul><ul><li>Homozygous/pure: identical alleles (HH or hh) </li></ul></ul><ul><ul><li>Heterozygous/hybrid: different alleles (Hh) </li></ul></ul><ul><li>Genotype vs. Phenotype: </li></ul><ul><ul><li>Genotype: genetic makeup (Tt) </li></ul></ul><ul><ul><li>Phenotype: physical appearance (tall) </li></ul></ul>
  11. 11. TestCross <ul><li>A testcross is used to determine the genotype of a parental organism </li></ul><ul><li>Cross the organism with the unknown genotype with an organism with the recessive phenotype </li></ul>
  12. 12. Law of Independent Assortment <ul><li>Each pair of alleles segregates into gametes independently </li></ul><ul><ul><li>Just because an organism gets one allele doesn’t mean it will get a certain other one </li></ul></ul><ul><ul><li>Example: </li></ul></ul><ul><ul><ul><li>Seed color (yellow or green) vs. Seed shape (round or wrinkled) </li></ul></ul></ul><ul><ul><ul><li>Yellow is NOT always with Round, etc… </li></ul></ul></ul><ul><ul><ul><li>Blonde hair does not HAVE to go with blue eyes </li></ul></ul></ul>
  13. 13. Probability <ul><li>Probability scale ranges from 0 to 1 </li></ul><ul><ul><li>If an event is certain to happen, it has a probability of 1 </li></ul></ul><ul><ul><li>If an event is certain NOT to happen, it has a probability of 0 </li></ul></ul><ul><ul><li>Getting heads on a coin toss is ½ (one out of two) </li></ul></ul>
  14. 14. The Rule of Multiplication <ul><li>To determine the chance that two or more independent events will occur together in a specific combination, compute the probability for each independent event and then multiply the individual probabilities to get the overall probability </li></ul><ul><li>Example: Rolling two dice and rolling a 3 on each </li></ul><ul><ul><li>1/6 X 1/6 </li></ul></ul><ul><ul><li>1/36 </li></ul></ul>
  15. 15. The Rule of Addition <ul><li>The probability of an event that can occur in two or more different ways is the sum of the separate possibilities of those ways </li></ul><ul><li>Rolling an odd number using a dice: </li></ul><ul><ul><li>1/6 + 1/6 + 1/6 = 3/6 (or ½) </li></ul></ul>
  16. 16. Incomplete Dominance <ul><li>F 1 hybrid is intermediate between the two parents </li></ul><ul><li>1:2:1 ratio </li></ul><ul><li>red: pink: white </li></ul>
  17. 17. Codominance <ul><li>Both alleles are separately manifested in the phenotype </li></ul><ul><ul><li>Example: Horses </li></ul></ul><ul><ul><ul><li>Brown hairs </li></ul></ul></ul><ul><ul><ul><li>Black hairs </li></ul></ul></ul><ul><ul><ul><li>Brown and Black hairs </li></ul></ul></ul>
  18. 18. Multiple Alleles <ul><li>Genes that exist in more than two allelic forms </li></ul><ul><li>Example: ABO Blood Typing </li></ul><ul><ul><li>I A I A , I A i </li></ul></ul><ul><ul><li>I B I B , I B i </li></ul></ul><ul><ul><li>I A I B </li></ul></ul><ul><ul><li>ii </li></ul></ul>
  19. 19. Pleiotropy <ul><li>Def’n: </li></ul><ul><ul><li>The ability of a gene to affect an organism in many ways </li></ul></ul><ul><li>Example: </li></ul><ul><ul><li>Alleles that cause sickle-cell anemia also cause other symptoms </li></ul></ul>
  20. 20. Epistasis <ul><li>Def’n: </li></ul><ul><ul><li>A gene at one locus (location) alters the phenotypic expression of a gene at another locus (location) </li></ul></ul><ul><ul><li>BB/Bb/bb determines coat color…BUT… </li></ul></ul><ul><ul><li>CC/Cc/cc determines pigment or not </li></ul></ul>
  21. 21. Polygenic Inheritance <ul><li>Many characteristics, including human skin color and height, vary along a continuum among the population </li></ul><ul><li>Polygenic inheritance is the effect of two or more genes put together on a single phenotypic characteristics </li></ul><ul><li>Example: Height determined by 3 genes </li></ul><ul><ul><li>AABBCC: very tall person (6’2”) </li></ul></ul><ul><ul><li>aabbcc: very short person (4’11”) </li></ul></ul><ul><ul><li>AaBbCc: intermediate height person (5’5”) </li></ul></ul>
  22. 22. Pedigrees <ul><li>A pedigree is a family tree that shows the interrelationships of parents and children across the generations </li></ul><ul><li>Used to predict patterns in the future (risk assessment) </li></ul>
  23. 23. Recessive Genetic Disorders <ul><li>Cystic Fibrosis (cc) </li></ul><ul><ul><li>Recessive disorder; most common in Caucasians </li></ul></ul><ul><ul><li>Cc (carrier) </li></ul></ul><ul><li>Tay-Sachs Disease (tt) </li></ul><ul><ul><li>Recessive disorder; most common in Ashkenazi Jews </li></ul></ul><ul><li>Sickle-Cell Anemia (aa) </li></ul><ul><ul><li>Recessive disorder; most common among African-Americans </li></ul></ul>
  24. 24. Societal Factors… <ul><li>The prevalence of recessive genetic disorders greatly increases when closely-related relatives interbreed </li></ul><ul><li>This is why many countries and cultures have laws against intermarriage among close relatives (cousins, etc.) </li></ul>
  25. 25. Dominant Genetic Disorders <ul><li>Dwarfism: </li></ul><ul><ul><li>DD or Dd = dwarf phenotype </li></ul></ul><ul><li>Huntington’s Disease: </li></ul><ul><ul><li>Aa or AA </li></ul></ul><ul><ul><li>Current research can now tell us whether or not a person has Huntington’s before symptoms set in </li></ul></ul><ul><ul><li>Ethical dilemma?? </li></ul></ul>

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