Mendelian Genetics <ul><li>Chapter 12, part 1 </li></ul>
Gregor Mendel <ul><li>Born in 1822 in Moravia (now part of the Czech Republic. </li></ul><ul><li>Son of a tenant farmer; j...
<ul><li>At the monastery in Brno, Moravia, Mendel received the support of Abbot Napp. </li></ul><ul><li>From 1851-1855, st...
<ul><li>What was understood at the time: </li></ul><ul><ul><li>Heredity appeared random and unpredictable. </li></ul></ul>...
<ul><li>With Abbot Napp’s encouragement, Mendel studied heredity in peas, carefully choosing traits that did not appear to...
<ul><li>Mendel presented his findings to the Association of Natural Research in Brno in 1865. </li></ul><ul><li>Few people...
<ul><li>In 1868, Mendel became abbot of his monastery. </li></ul><ul><li>His religious work left little time for research,...
<ul><li>Mendel died in 1884. Sixteen years later, in 1900, his work was rediscovered by Hugo de Vries and others looking f...
<ul><li>A scientific law is an evidence-based  description  of a natural phenomenon in a given set of circumstances.  </li...
Three Laws of Heredity <ul><li>Law of Dominance </li></ul><ul><li>Law of Segregation </li></ul><ul><li>Law of Independent ...
<ul><li>“Dominant” is one of those pesky words with multiple meanings that can interfere with our understanding of how it ...
Law of Dominance <ul><li>Traits are controlled by two factors that can be called “dominant” or “recessive.” </li></ul><ul>...
X In this cross between two purple-flowered pea plants, one-quarter of the offspring have white flowers. Based just on thi...
The offspring of a purple-flowered pea plant and a white-flowered pea plant all have purple flowers. The purple trait is d...
Offspring of the F1 generation (the hybrids) may be purple-flowered if they inherit at least one factor for purple flowers...
The purple-flowered trait is dominant because each an individual who inherits at least one copy of the purple allele (R) s...
Solving problems involving dominance Dexter has freckles. So does his wife, Darla. Their son, Derek has no freckles. Is ha...
<ul><li>Fred and Wilma both have smooth hairlines. Their daughter, Pebbles, has a pointed (“widow’s peak”) hairline. Which...
Law of Segregation <ul><li>Each individual has a pair of factors controlling each trait, one inherited from each biologica...
gametes homozygous parent A A A A In modern terms, the homozygous parents in the P generation can pass one one kind of all...
The heterozygous parents of the F1 generation have two alleles for the gene in question, and can pass one or the other, bu...
The  genotypes  can be represented with letters, which symbolize the alleles: capital for dominant alleles, small case for...
When the gametes join to produce the F1 generation, all offspring of homozygous dominant and homozygous recessive parents ...
sperm eggs F 2 offspring P p + P p p p + + + P P P p P p PP pp gametes from F 1  plants (Pp) The heterozygous F1 individua...
P p sperm eggs P p 1/4 1/4 1/4 1/4 1/2 1/2 1/2 1/2 PP P p p P pp P p self-fertilize A Punnet square is one way to predict ...
Solving single-gene (monohybrid) crosses with Mendelian (dominant-recessive) inheritance. Tomato fruit color can be red or...
Solving single-gene (monohybrid) crosses with Mendelian (dominant-recessive) inheritance. Tomato fruit color can be red or...
<ul><li>Flat feet are caused by a recessive allele (f). Both Bert and his wife Betsy have normal feet, but their first chi...
<ul><li>Prominent chin dimples are inherited by a dominant allele (D). Herman has a prominent chin dimple. So does his fat...
<ul><li>Leslie has a long palmar muscle (third tendon in the middle of the wrist). Her twin brother Louis does not. Neithe...
<ul><li>When genetic factors segregate in the gametes, they segregate independently of one another. A dominant allele for ...
Dominant form  Recessive form Trait Seed shape Seed color Pod color Pod shape Flower color Flower location Plant size tall...
meiosis II meiosis I pairs of alleles on homologous chromosomes in diploid cells chromosomes replicate orienting like this...
meiosis II meiosis I chromosomes replicate orienting like this or like this replicated homologues pair during metaphase of...
SY SY s Y s Y S y S y sy sy SSYY S s YY ss YY ssy Y S sy Y SSY y S s Y y S syy SS yy SS y Y s SYY s S y Y s SY y ss Y y ss...
Solving dihybrid crosses with Mendelian (dominant-recessive) inheritance. Pea plants can be tall (T) or short (t) and prod...
Solving dihybrid crosses with Mendelian (dominant-recessive) inheritance. Pea plants can be tall (T) or short (t) and prod...
<ul><li>A pea plant with purple (P) flowers and yellow (Y) seeds is crossed with a pea plant with white flowers (p) and gr...
<ul><li>A gardener has a tall tall (T) pea plants with smooth (S) seeds. She crosses it with a plant that is also tall and...
<ul><li>Mendel’s Laws were good descriptions of what he observed in the peas and other plants he worked with. </li></ul><u...
Recap <ul><li>Genes may have multiple alleles, such as dominant and recessive alleles. </li></ul><ul><li>Chromosomes, whic...
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  1. 1. Mendelian Genetics <ul><li>Chapter 12, part 1 </li></ul>
  2. 2. Gregor Mendel <ul><li>Born in 1822 in Moravia (now part of the Czech Republic. </li></ul><ul><li>Son of a tenant farmer; joined a monastery to get an education. </li></ul><ul><li>Deeply interested in science, particularly heredity. </li></ul>
  3. 3. <ul><li>At the monastery in Brno, Moravia, Mendel received the support of Abbot Napp. </li></ul><ul><li>From 1851-1855, studied at the University of Vienna, but did not receive a degree. </li></ul>
  4. 4. <ul><li>What was understood at the time: </li></ul><ul><ul><li>Heredity appeared random and unpredictable. </li></ul></ul><ul><ul><li>Many traits seemed to blend in the offspring, suggesting a liquid factor controlled heredity. </li></ul></ul><ul><ul><li>Yet some traits, such as red hair, did not blend away. </li></ul></ul>
  5. 5. <ul><li>With Abbot Napp’s encouragement, Mendel studied heredity in peas, carefully choosing traits that did not appear to blend. Collected data from 1856 - 1865. </li></ul><ul><li>Mendel’s creative contribution: he was the first to follow single traits from generation to generation instead of trying to document and follow every trait in the plants. </li></ul>
  6. 6. <ul><li>Mendel presented his findings to the Association of Natural Research in Brno in 1865. </li></ul><ul><li>Few people recognized the significance of Mendel’s research. His quantitative methods were uncommon at the time, and the “blending” theory was widely accepted. </li></ul>
  7. 7. <ul><li>In 1868, Mendel became abbot of his monastery. </li></ul><ul><li>His religious work left little time for research, which he set aside, though he was always convinced he had made a valuable contribution to science. </li></ul>
  8. 8. <ul><li>Mendel died in 1884. Sixteen years later, in 1900, his work was rediscovered by Hugo de Vries and others looking for clues into the puzzle of heredity. </li></ul><ul><li>Though criticized in some details, the main body of Mendel’s work still stands. </li></ul>
  9. 9. <ul><li>A scientific law is an evidence-based description of a natural phenomenon in a given set of circumstances. </li></ul><ul><li>Mendel’s three Laws of Heredity describe what Mendel observed in patterns of inherited traits. </li></ul>Mendel’s Laws
  10. 10. Three Laws of Heredity <ul><li>Law of Dominance </li></ul><ul><li>Law of Segregation </li></ul><ul><li>Law of Independent Assortment </li></ul>
  11. 11. <ul><li>“Dominant” is one of those pesky words with multiple meanings that can interfere with our understanding of how it is used in science. First, list several meanings that you can think of for the word “dominant.” </li></ul><ul><li>Now write out what you believe is meant by a “dominant” trait. </li></ul>
  12. 12. Law of Dominance <ul><li>Traits are controlled by two factors that can be called “dominant” or “recessive.” </li></ul><ul><li>A “dominant” trait shows if the offspring inherits at least one dominant factor from one parent. </li></ul><ul><li>A “recessive” trait shows only if the offspring inherits two recessive factors, one from each parent. </li></ul>
  13. 13. X In this cross between two purple-flowered pea plants, one-quarter of the offspring have white flowers. Based just on this information, which is dominant: white or purple flowers? How do you know? Hint: “Dominance” is not based on numbers of individuals with the trait. It is based on the number of copies of the allele that must be inherited to show the trait.
  14. 14. The offspring of a purple-flowered pea plant and a white-flowered pea plant all have purple flowers. The purple trait is dominant. Why? true-breeding, purple-flowered plant First-generation offspring (F 1 ) Parental generation (P) pollen pollen cross-fertilize true-breeding, white-flowered plant RR rr Rr
  15. 15. Offspring of the F1 generation (the hybrids) may be purple-flowered if they inherit at least one factor for purple flowers, or may be white flowered if they inherit the white factor from both parents. 1/4 white Second- generation offspring (F 2 ) First- generation offspring (F 1 ) 3/4 purple X Rr Rr RR Rr Rr rr
  16. 16. The purple-flowered trait is dominant because each an individual who inherits at least one copy of the purple allele (R) shows the purple phenotype. The white-flowered trait is recessive because an individual must inherit two copies of the white allele (r) to show the white phenotype. RR or Rr rr genotypes: phenotype purple white
  17. 17. Solving problems involving dominance Dexter has freckles. So does his wife, Darla. Their son, Derek has no freckles. Is having freckles a dominant or a recessive trait? Let’s start by making a family tree:
  18. 18. <ul><li>Fred and Wilma both have smooth hairlines. Their daughter, Pebbles, has a pointed (“widow’s peak”) hairline. Which is dominant: smooth or pointed hairline? How do you know? </li></ul><ul><li>Penelope has small, attached earlobes. Armando has larger, free earlobes. All four of their children have large, free earlobes. Which is dominant: free or attached earlobes? How do you know? </li></ul>
  19. 19. Law of Segregation <ul><li>Each individual has a pair of factors controlling each trait, one inherited from each biological parent. </li></ul><ul><li>During the formation of gametes (sex cells) these two factors separate. Only one ends up in each sex cell. </li></ul>
  20. 20. gametes homozygous parent A A A A In modern terms, the homozygous parents in the P generation can pass one one kind of allele to their offspring. Homologous chromosomes gene
  21. 21. The heterozygous parents of the F1 generation have two alleles for the gene in question, and can pass one or the other, but not both, to their offspring. gametes heterozygous parent A a A a Homologous chromosomes gene
  22. 22. The genotypes can be represented with letters, which symbolize the alleles: capital for dominant alleles, small case for recessive. all p sperm and eggs all P sperm and eggs purple parent white parent pp PP P P p p + +
  23. 23. When the gametes join to produce the F1 generation, all offspring of homozygous dominant and homozygous recessive parents are heterozygous. P p p P + + or P p P p sperm eggs F 1 offspring gametes of parents
  24. 24. sperm eggs F 2 offspring P p + P p p p + + + P P P p P p PP pp gametes from F 1 plants (Pp) The heterozygous F1 individuals can put either a dominant OR a recessive allele in each of their gametes.
  25. 25. P p sperm eggs P p 1/4 1/4 1/4 1/4 1/2 1/2 1/2 1/2 PP P p p P pp P p self-fertilize A Punnet square is one way to predict the outcome of a cross by showing all the possible combinations of all the possible gametes.
  26. 26. Solving single-gene (monohybrid) crosses with Mendelian (dominant-recessive) inheritance. Tomato fruit color can be red or yellow. a. A red tomato plant is crossed with a yellow tomato plant, and all the offspring have red tomatoes. Which trait is dominant? b. If two of the resulting hybrid red tomato plants are crossed, what will be the ratio of phenotypes in the offspring?
  27. 27. Solving single-gene (monohybrid) crosses with Mendelian (dominant-recessive) inheritance. Tomato fruit color can be red or yellow. a. A red tomato plant is crossed with a yellow tomato plant, and all the offspring have red tomatoes. Which trait is dominant? b. If two of the resulting hybrid red tomato plants are crossed, what will be the ratio of phenotypes in the offspring?
  28. 28. <ul><li>Flat feet are caused by a recessive allele (f). Both Bert and his wife Betsy have normal feet, but their first child, Binky, has flat feet. </li></ul><ul><ul><li>What are the genotypes of Bert, Betsy, and Binky? </li></ul></ul><ul><ul><li>What are the odds of Bert and Betsy’s next child having flat feet? </li></ul></ul>
  29. 29. <ul><li>Prominent chin dimples are inherited by a dominant allele (D). Herman has a prominent chin dimple. So does his father, but not his mother. Herman’s wife, Honoria, has no chin dimple. What is the probability that Herman and Honoria’s first child will have a prominent chin dimple? How do you know? </li></ul>
  30. 30. <ul><li>Leslie has a long palmar muscle (third tendon in the middle of the wrist). Her twin brother Louis does not. Neither do their parents. Leslie’s husband, Lamont, has the long palmar muscle. So do their twin sons, Larry and Lance. Is the long palmar muscle dominant or recessive? How do you know? (It may help to make a family tree for this problem.) </li></ul>
  31. 31. <ul><li>When genetic factors segregate in the gametes, they segregate independently of one another. A dominant allele for one trait does not guarantee inheritance of a dominant allele for a different trait. </li></ul>Law of Independent Assortment
  32. 32. Dominant form Recessive form Trait Seed shape Seed color Pod color Pod shape Flower color Flower location Plant size tall (1.8 to 2 meters) dwarf (0.2 to 0.4 meters) constricted purple white green green yellow wrinkled smooth at leaf junctions at tips of branches inflated yellow All organisms have multiple inheritable traits controlled by genes. Each trait is inherited independently of the others. A pea plant may, for example, have yellow seeds (dominant) but white flowers (recessive).
  33. 33. meiosis II meiosis I pairs of alleles on homologous chromosomes in diploid cells chromosomes replicate orienting like this or like this replicated homologues pair during metaphase of meiosis I, independent assortment produces four equally likely allele combinations during meiosis S Y s y S S S S S S S S S S Y Y Y Y Y Y Y Y Y Y s s s s s s s s s s y y y y y y y y y y Traits carried on separate chromosomes sort independently of one another during gamete formation. Notice that each gamete receives ONE s-bearing and ONE y-bearing chromosome from the original cell.
  34. 34. meiosis II meiosis I chromosomes replicate orienting like this or like this replicated homologues pair during metaphase of meiosis I, independent assortment produces four equally likely allele combinations during meiosis S Y s y S S S S S S S S S S Y Y Y Y Y Y Y Y Y Y s s s s s s s s s s y y y y y y y y y y Now consider this in terms of genotypes: Genotype of this parent (for these two traits) is SsYy Genotypes of the gametes that this parent can produce are: SY sy Sy sY Meiosis puts ONE S-bearing and one Y-bearing chromosome in each gamete.
  35. 35. SY SY s Y s Y S y S y sy sy SSYY S s YY ss YY ssy Y S sy Y SSY y S s Y y S syy SS yy SS y Y s SYY s S y Y s SY y ss Y y ssyy s S yy 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 1/16 eggs sperm S s Y y self-fertilize seed shape seed color phenotypic ratio (9:3:3:1) 3/4 3/4 9/16 smooth yellow smooth yellow =  3/4 1/4 3/16 smooth green smooth green =  1/4 3/4 3/16 wrinkled yellow wrinkled green =  1/4 1/4 1/16 wrinkled green wrinkled yellow =  This Punnet square shows a cross between two pea plants which are heterozygous for two traits. Again, the Punnet square represents all possible combinations of the gametes that the plants can donate to their offspring. They must put one copy of a gene for each trait in their gametes.
  36. 36. Solving dihybrid crosses with Mendelian (dominant-recessive) inheritance. Pea plants can be tall (T) or short (t) and produce purple (R) or white (r) blossoms. a. A pure-breeding tall plant with purple flowers (TTRR) is crossed with a pure-breeding short plant with white flowers (ttrr). What will the offspring look like? b. If two of the hybrid (F1) plants are crossed, what offspring can they produce?
  37. 37. Solving dihybrid crosses with Mendelian (dominant-recessive) inheritance. Pea plants can be tall (T) or short (t) and produce purple (R) or white (r) blossoms. a. A pure-breeding tall plant with purple flowers (TTRR) is crossed with a pure-breeding short plant with white flowers (ttrr). What will the offspring look like? b. If two of the hybrid (F1) plants are crossed, what offspring can they produce?
  38. 38. <ul><li>A pea plant with purple (P) flowers and yellow (Y) seeds is crossed with a pea plant with white flowers (p) and green seeds (y). All of the plants in the next generation have purple flowers and yellow seeds. If two plants from this hybrid generation are crossed, what will their offspring look like? Do a dihybrid Punnet square to predict the outcome. </li></ul>
  39. 39. <ul><li>A gardener has a tall tall (T) pea plants with smooth (S) seeds. She crosses it with a plant that is also tall and with smooth seeds, BUT she knows this plant is the offspring between a pure-breeding tall plant with smooth seeds plant and a pure-breeding short plant with wrinkled seeds. What will the the results of the pure-breeding tall/smooth plant and the hybrid plant? </li></ul>
  40. 40. <ul><li>Mendel’s Laws were good descriptions of what he observed in the peas and other plants he worked with. </li></ul><ul><li>New knowledge accumulated since Mendel’s time has refined his ideas. While his laws still hold true in some instances, there are many exceptions that we will explore in the next presentations. </li></ul>Laws: “proven” forever?
  41. 41. Recap <ul><li>Genes may have multiple alleles, such as dominant and recessive alleles. </li></ul><ul><li>Chromosomes, which carry genes, separate from one another during gamete formation. </li></ul><ul><li>Chromosomes sort independently of one another during gamete formation, but each gamete gets ONE of each kind of chromosome. </li></ul>
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