Fundamentals of Genetics        Chapter 9
Mendel’s Legacy• Genetics is the study of how characteristics  are transmitted from parents to offspring  – Founded with t...
Gregor Mendel• Mendel conducted experiments at the  monastery with pea plants• He researched heredity – the transmission o...
Mendel’s Garden Peas• Mendel observed seven characteristics of pea  plants• Each characteristic occurred in two contrastin...
Mendel’s Garden PeasCharacteristic                Trait• Position of flowers along  stem• Height of plant
Mendel’s Garden PeasCharacteristic      Trait• Pod Appearance• Pod color
Mendel’s Garden PeasCharacteristic       Trait• Seed Texture• Seed color• Flower color
Mendel’s Methods• Mendel controlled pollination  – Self-pollination – pollen fertilizes egg cells on the    same flower  –...
Mendel’s Experiments• P generation – parent generation• F1 (first filial) generation – offspring of the P  generation• F2 ...
Mendel’s Experiments• First he grew true-  breeding plants   – A plant that is true-     breeding, or pure, for a     trai...
Mendel’s Experiments• Next, he cross-  pollinated true-  breeding parents of  the P generation• What do you think  the F1 ...
Mendel’s Experiments• The F1 generation was  all purple flowers!
Mendel’s Experiments• Next, he let the flowers from the F1 generation  self-pollinate• What do you think the F2 generation...
Mendel’s Experiments• The F2 generation came  out with 75% purple  flowers and 25% white  flowers!
Mendel’s Results and Conclusions• Mendel’s observations led him to hypothesize  that something within the pea plants  cont...
Recessive and Dominant Traits• Dominant – trait that masks the factor for the  other trait• Recessive – trait that is mask...
The Law of Segregation• The law of segregation states that a pair of  factors is segregated, or separated, during the  for...
The Law of Independent Assortment• The law of independent  assortment states that  factors separate  independently of one ...
Support for Mendel’s Conclusions• A gene is a segment of a chromosome that  controls a particular hereditary trait• The di...
Section 2GENETIC CROSSES
Genotype and Phenotype• Genotype – an organism’s genetic makeup (PP,  Pp, pp)• Phenotype – an organism’s physical  appeara...
Genotype and Phenotype• Homozygous – both alleles of a pair are alike  (PP = homozygous dominant and  pp = homozygous rece...
Probability• Probability – the likelihood that a specific  event will occur
Predicting Results of Monohybrid                Crosses• In a monohybrid cross, one characteristic is  tracked• Biologists...
Ex 1: Homozygous X Homozygous• TT x tt (T = tall, t =  short)• Possible Genotypes   – 100% Tt• Possible Phenotypes   – 100...
Ex 2: Homozygous X Heterozygous• BB X Bb (B = black hair,  b = brown hair)• Possible Genotypes   – 50% BB, 50% Bb• Possibl...
Ex 3: Heterozygous X Heterozygous• Bb X Bb(B = black hair,  b = brown hair)• Possible genotypes   – 25% BB, 50%Bb, 25% bb•...
Ex 4: Testcross• How could you determine whether a black  guinea pig is homozygous (BB) or  heterozygous (Bb)?• By complet...
Ex 5: Incomplete Dominance• Incomplete dominance occurs when the  phenotype of heterozygous individual is in  between the ...
Ex 5: Incomplete Dominance• RW X RW (R = red, W =  white)• Possible genotypes and  phenotypes  – 25% RR, red  – 50% RW, pi...
Ex 6: Codominance• In codominance, both alleles contribute to the  phenotype• In some varieties of chicken, the allele for...
Ex 6: Codominance• F W FW X F B F B  (F = feathers, B = black,  W = white• Possible genotypes and  phenotypes   – 100% FWF...
Predicting Results of Dihybrid Crosses• A dihybrid cross is a cross in which two  characteristics are tracked• More compli...
Dihybrid Homozygous X Homozygous• rryy X RRYY (R= round, r= wrinkled, Y= yellow,  y= green)
Dihybrid Heterozygous X Heterozygous• RrYy X RrYy
Chapter 9 notes
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Chapter 9 notes

  1. 1. Fundamentals of Genetics Chapter 9
  2. 2. Mendel’s Legacy• Genetics is the study of how characteristics are transmitted from parents to offspring – Founded with the work of Gregor Mendel, an Austrian monk
  3. 3. Gregor Mendel• Mendel conducted experiments at the monastery with pea plants• He researched heredity – the transmission of characteristics from parents to offspring
  4. 4. Mendel’s Garden Peas• Mendel observed seven characteristics of pea plants• Each characteristic occurred in two contrasting traits – genetically determined variants of a characteristic
  5. 5. Mendel’s Garden PeasCharacteristic Trait• Position of flowers along stem• Height of plant
  6. 6. Mendel’s Garden PeasCharacteristic Trait• Pod Appearance• Pod color
  7. 7. Mendel’s Garden PeasCharacteristic Trait• Seed Texture• Seed color• Flower color
  8. 8. Mendel’s Methods• Mendel controlled pollination – Self-pollination – pollen fertilizes egg cells on the same flower – Cross-pollination – pollen fertilizes egg cells on flowers of different plants
  9. 9. Mendel’s Experiments• P generation – parent generation• F1 (first filial) generation – offspring of the P generation• F2 (second filial) generation – offspring of the F1 generation
  10. 10. Mendel’s Experiments• First he grew true- breeding plants – A plant that is true- breeding, or pure, for a trait always produces offspring with that trait when they self-pollinate
  11. 11. Mendel’s Experiments• Next, he cross- pollinated true- breeding parents of the P generation• What do you think the F1 generation looked like?
  12. 12. Mendel’s Experiments• The F1 generation was all purple flowers!
  13. 13. Mendel’s Experiments• Next, he let the flowers from the F1 generation self-pollinate• What do you think the F2 generation looked like?
  14. 14. Mendel’s Experiments• The F2 generation came out with 75% purple flowers and 25% white flowers!
  15. 15. Mendel’s Results and Conclusions• Mendel’s observations led him to hypothesize that something within the pea plants controlled the characteristics observed – He called these controls factors• Because the characteristics had two alternative forms, he reasoned that a pair of factors must control each trait
  16. 16. Recessive and Dominant Traits• Dominant – trait that masks the factor for the other trait• Recessive – trait that is masked by the factor for the other trait
  17. 17. The Law of Segregation• The law of segregation states that a pair of factors is segregated, or separated, during the formation of gametes
  18. 18. The Law of Independent Assortment• The law of independent assortment states that factors separate independently of one another during the formation of gametes
  19. 19. Support for Mendel’s Conclusions• A gene is a segment of a chromosome that controls a particular hereditary trait• The different forms of a gene are called alleles – Capital letters are used to represent dominant alleles – Lowercased letters are used to represent recessive alleles
  20. 20. Section 2GENETIC CROSSES
  21. 21. Genotype and Phenotype• Genotype – an organism’s genetic makeup (PP, Pp, pp)• Phenotype – an organism’s physical appearance (purple flower, white flower)
  22. 22. Genotype and Phenotype• Homozygous – both alleles of a pair are alike (PP = homozygous dominant and pp = homozygous recessive)• Heterozygous – two alleles are different (Pp)
  23. 23. Probability• Probability – the likelihood that a specific event will occur
  24. 24. Predicting Results of Monohybrid Crosses• In a monohybrid cross, one characteristic is tracked• Biologists use a Punnett square to predict the probable distribution of inherited traits in the offspring
  25. 25. Ex 1: Homozygous X Homozygous• TT x tt (T = tall, t = short)• Possible Genotypes – 100% Tt• Possible Phenotypes – 100% tall
  26. 26. Ex 2: Homozygous X Heterozygous• BB X Bb (B = black hair, b = brown hair)• Possible Genotypes – 50% BB, 50% Bb• Possible Phenotypes – 100% black
  27. 27. Ex 3: Heterozygous X Heterozygous• Bb X Bb(B = black hair, b = brown hair)• Possible genotypes – 25% BB, 50%Bb, 25% bb• Possible phenotypes – 75% black hair, 25% brown hair
  28. 28. Ex 4: Testcross• How could you determine whether a black guinea pig is homozygous (BB) or heterozygous (Bb)?• By completing a testcross – an individual with an unknown genotype is crossed with a homozygous recessive individual
  29. 29. Ex 5: Incomplete Dominance• Incomplete dominance occurs when the phenotype of heterozygous individual is in between the two homozygous phenotypes
  30. 30. Ex 5: Incomplete Dominance• RW X RW (R = red, W = white)• Possible genotypes and phenotypes – 25% RR, red – 50% RW, pink – 25% WW, white
  31. 31. Ex 6: Codominance• In codominance, both alleles contribute to the phenotype• In some varieties of chicken, the allele for black feathers is codominant with the allele for white feathers – Heterozygous chickens are speckled with black and white feathers
  32. 32. Ex 6: Codominance• F W FW X F B F B (F = feathers, B = black, W = white• Possible genotypes and phenotypes – 100% FWFB, speckled
  33. 33. Predicting Results of Dihybrid Crosses• A dihybrid cross is a cross in which two characteristics are tracked• More complicated than monohybrid crosses because more combinations of alleles are possible
  34. 34. Dihybrid Homozygous X Homozygous• rryy X RRYY (R= round, r= wrinkled, Y= yellow, y= green)
  35. 35. Dihybrid Heterozygous X Heterozygous• RrYy X RrYy

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