AP BIo Ch. 14


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AP BIo Ch. 14

  1. 1. W m up ar  Match the items on the left with one item on the right 1. HH A. heterozygous 2. Curly hair B. homozygous 3. Hh C. phenotype 4. Genotype D. tt
  2. 2. Hel pf ul Bozeman Biology Crash Course Biology  Hank Green  Paul Anderson
  3. 3. Inheritance Part 1
  4. 4. Main Topics       Gregor Mendel’s work Mendel’s Laws Dominant/recessive Heterozygous/homozygous Alleles Codominance and incomplete dominance
  5. 5. The father of genetics  Gregor Mendel is considered the Father of Genetics  Born in 1822  Studied math & physics at an Austrian university  He was the first person to study how traits are passed along from one generation to the next.  He did his work with the pea plant Who’s your daddy?
  6. 6. Mendel’s Garden  Analyzed observable traits of peas growing in his monastery garden.
  7. 7. Mendel’s Garden  Eight years & 20 volumes of data and analysis on 7 distinctive traits  Published in 1865
  8. 8. Why peas?  The garden pea was a good choice for a variety of reasons. The garden pea:     is easy to raise produces large numbers of offspring reproduces quickly has flowers which are self fertilizing but can be easily crossed to other varieties
  9. 9. Experimental Approach  Can also be cross-fertilized by human manipulation
  10. 10.  Mendel cross-fertilized true-breeding garden pea plants having clearly contrasting traits
  11. 11. Allele for purple flowers Locus for flower-color gene Allele for white flowers Homologous pair of chromosomes
  12. 12. Mendel's Theory of Segregation  Diploid organisms inherit two genes per trait  Each gene segregates from the other during meiosis so that each gamete will receive only one gene per trait
  13. 13. How can the Chances of an Offspring’s Traits be Determined?  The chance of an offspring showing a certain trait can be determined by using the Punnett square.  The table contains spaces for the parent’s gametes and the possible offspring from that mating.  The alleles are represented by their letters.  Genes come in pairs and must be separated during gamete formation.  These gametes (letter) of each pair are placed in each of the outside spaces.  They are then combined to form the possible offspring.
  14. 14. Punnett Square: Bb X Bb Gametes B b B BB Bb b Bb bb
  15. 15. Monohybrid Crosses  Mendel's first experiments  One trait  Monohybrid crosses have two parents that are true-breeding for contrasting forms of a trait.
  16. 16.  All the offspring from the first cross showed only 1 form of the trait  This trait seemed “stronger” so he called it DOMINANT  When he crossed the offspring from the first cross, the other form of the trait reappeared, but only 1/4 of the time  This trait seemed “weaker” so he called it recessive
  17. 17. Predicting the Outcome Why does one form of the trait disappear in the first generation (F1 ), only to show up in the second generation (F2 )??
  18. 18. Prevailing Theories  Artificial selection: populations could evolve (i.e. change) if members show variation in heritable traits  Variations that improved survival chances in the wild would be more common in each generation  This idea is known as natural selection
  19. 19. Mendel’s Experiments  Natural selection did not fit with prevailing view of inheritance-blending  Blending would produce uniform populations; such populations could not evolve
  20. 20. Mendel’s Experiments  Many observations did not fit blending  A white horse and a black horse did not produce only gray horses
  21. 21. Test (Back) Crosses  To support his concept of segregation, Mendel crossed F1 plants (Pp) BACK with homozygous recessives (pp) What ratio would Mendel have gotten? He didn’t know the letter combination of the F1 plants. The test (back) cross allowed him to figure it out
  22. 22. His back crossed supported his idea of 2 “factors” for each individual, and the idea that those “factors” are segregated Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If Pp, then 2 offspring purple and 1 2 offspring white: If PP, then all offspring purple: p 1 p P p p Pp Pp pp pp P Pp Pp P P Pp Pp
  23. 23. Dihybrid Crosses  Mendel also performed experiments involving two traits
  24. 24. Predicting the Outcome What is the predicted PHENOTYPIC ratio and the predicted GENOTYPIC ratio that Mendel saw?
  25. 25. Predicting the Outcome  The F2 results showed 9/16 were tall and purpleflowered and 1/16 were dwarf and whiteflowered-as were the original parents; however, there were 3/16 each of two new combinations: dwarf purple-flowered and tall white-flowered.
  26. 26. Out com es Monohybrid crosses Both parents HETEROZYGOUS 3:1 phenotype Dihybrid crosses Both parents HETEROZYGOUS 9:3:3:1 phenotype
  27. 27. Theory of Independent Assortment  Each gene of a pair tends to assort into gametes independently of other gene pairs on non-homologous chromosomes
  28. 28. Theory in Modern Form  Genes located on nonhomologous chromosomes segregate independently of each other
  29. 29. Mendel’s Work  The work that Mendel did helped explain patterns of inheritance in eukaryotes.  But Mendel worked with traits that had a clear dominant/recessive pattern.  Also, the traits he worked with were all controlled by a single gene.
  30. 30. Different Patterns of Inheritance  As we now know, many traits do not follow Mendelian Inheritance patterns.
  31. 31. Co-dominance  When both alleles are expressed equally in the heterozygous individual.  A and B blood type alleles are co-dominant, because a person with AB genotype will have both A and B blood proteins.  Black and orange color in cats are co-dominant, because a heterozygous female will have both orange and black hair.
  32. 32. Incomplete Dominance  Both alleles are blended together in the heterozygous individual.  Dominant allele cannot completely mask the expression of another
  33. 33. Practice with your neighbor  For the following questions  Work with your neighbor to answer the question.  Answer the multiple choice question then,  Use your notes to determine which one of Mendel’s principles it demonstrates
  34. 34. 1. A father carries 2 alleles for the gene for widow’s peak. He carries one dominant allele and one recessive allele. His gametes will a. b. c. d. All contain the dominant allele All contain the recessive allele ½ will get the dominant allele and ½ will get the recessive allele Each gamete will get both the dominant and the recessive allele
  35. 35. Which principle does question number one best demonstrate?  Principle of Segregation The dominant allele goes to one gamete and the recessive allele goes to another gamete
  36. 36. 2. A mother that is homozygous dominant for bushy eyebrows (BB) and heterozygous for round ears (Rr). The gametes she can make will a. All have a B and a R in them b. ½ will have a B and ½ will have a R or a r in them c. ½ will have a B and a R and ½ will have b and r d. ½ will have B and R and ½ will have B and r
  37. 37. What principle does number 2 demonstrate?  The Principle of Independent Assortment  All gametes will have a B, since mom only has B.  The big B can be with the big R or the big B can be with the little r.
  38. 38. 3. In meiosis, a diploid cell divides twice to form 4 haploid gametes. Each gamete contains: a. A complete set of DNA identical to the parents b. A ½ set of DNA, with just one copy of each chromosome c. Homologous pairs of chromosomes d. Multiple copies of chromosomes, depending on which ones moved during meiosis
  39. 39. Which one of Mendel’s Principles does number 3 demonstrate?  Principle of Segregation  All the homologous pairs of chromosomes separate so that there is just one of each pair in each gamete.
  40. 40. 4. When Mendel crossed a true breeding green pea plant (GG) with a true breeding yellow pea plant (gg), the offspring plants were a. b. c. d. All green All yellow ½ green and ½ yellow Green and yellow mixed
  41. 41. Which one of Mendel’s principles does number 4 demonstrate?  Principle of Complete Dominance  All offspring were Gg, and the dominant allele (G) masked the recessive allele (g)
  42. 42. 5. Mendel wanted to know if the color for pea seeds was linked to the shape of the pea seeds. He crossed a green, wrinkled seed plant (Ggrr) with a yellow, smooth seed (ggRr) plant. The offspring produced were: a. b. c. d. e. All green and wrinkled All yellow and wrinkled All green and smooth All yellow and smooth Some of each of the above
  43. 43. Which one of Mendel’s Principles does number 5 demonstrate?  Principle of Independent Assortment  The green trait can go with the smooth or the wrinkled trait  The yellow trait can go with the smooth or the wrinkled trait
  44. 44. Multiple Alleles  traits controlled by more that one gene (2 alleles) and so they have many different possible phenotypes.  These alleles can show dominant/recessive patterns or codominant patterns.
  45. 45. Bl ood Types Genotype of Phenotype of offspring offspring iAiA A iAi i i AB A iBiB iBi ii AB B B o
  46. 46. Rh f act or Rh factor Rh+ Rh- Possible genotypes +/+ or +/- -/-
  47. 47. X-linked traits  genes found on the X chromosome.  show different inheritance patterns in men than in women.  X-linked traits may show dominant/recessive or codominant patterns.
  48. 48. X-linked traits  Women have 2 Xchromosomes, men have an X and a Y.  For women to express a recessive phenotype, they must inherit 2 Xchromosomes, both with the recessive allele.  For men to express the recessive phenotype, they need only 1 recessive X
  49. 49. Multifactorial Inheritance  traits controlled by multiple alleles and the phenotypes can also be affected by the environment.  The environment can include exposure to sunlight, chemicals, hormones from the mother during pregnancy, etc.
  50. 50. DNA in organelles  DNA is also found in mitochondria and chloroplasts.  Mitochondrial DNA is only passed from Mother to child.