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Genetics

Genetics. Mendel and the Gene Idea. Multifactorial Inheritance. Genotype does not rigidly define the phenotype, but a range of possibilities over which the environment can influence genes + environment & diet phenotype. Phenotype depends on environment and genes.

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Genetics

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  1. Genetics Mendel and the Gene Idea

  2. Multifactorial Inheritance • Genotype does not rigidly define the phenotype, but a range of possibilities over which the environment can influence • genes + environment & diet phenotype

  3. Phenotype depends on environment and genes • Tree: leaves that vary in size, shape, and greenness, depending on exposure to wind and sun. • Humans: nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests. • Identical twins: genetic equals, accumulate phenotypic differences as a result of their unique experiences.

  4. Environment contributes to the phenotype acidic soil basic soil

  5. Early Ideas about Heredity • Before Mendel • basic facts of heredity • studied garden pea plant • formed hybrids • found recessive traits in some offspring

  6. Gregor Mendel • father of genetics • mentors - physics, botany • quantified results • subject - garden pea plant • 1843 – entered monastery • 1851-53 – studied at U of Vienna • 1857 – began breeding pea plants

  7. Advantages of peas • Mendel had strict control over which plants mated with which • Each pea plant has male (stamens) and female (carpal) sexual organs. • Mendel could allow self- pollination or also move pollen from one plant to another to cross-pollinate

  8. Mendel’s Seven Characters and Alleles

  9. Mendel’s Experimental Design • self-pollinate • crossed alternative traits to produce hybrids (hybrids expressed only dominant traits) • hybrids were self-pollinated (produced 3:1 ratio)

  10. Reginald Crundall Punnett Punnett square

  11. Symbols • P = parental generation • F1 = first filial generation • F2 = second filial generation

  12. Terminology • homozygous • homozygous dominant = RR • homozygous recessive= rr • heterozygous = Rr • genotype and phenotype • complete dominance

  13. Monohybrid Cross • parental varieties differ in a single character • character = flower color (using letter P) • allelles purple, dominant (PP, Pp) white, recessive (pp)

  14. Flower Color (Pea plant) topveg.com/wp-content/uploads/2009/03/pea-flower-ambience-300x286.jpg australianmajestictours.com/hovea.jpg

  15. Monohybrid CrossF1 • purple (PP) X white (pp) • dominant x recessive • F1 are all purple (Pp) • all Pp = hybrid

  16. Monohybrid Cross Ratio in F2 • phenotypic ratio 3:1 • 3 dominant: 1 recessive • PP & Pp are indistinguishable in complete dominance • genotypic ratio 1:2:1 • 1 homozygous dominant (PP) • 2 heterozygous (Pp) • 1 homozygous recessive (pp)

  17. Testcross (Pedigree Analysis) • to determine unknown genotype • utilizes a homozygous recessive • phenotypic ratio of offspring determines genotype F2 F1 P

  18. Example B_ B_ • F2 • 75% are black (B_) • 25% are brown (bb) B_ bb Bb BBBBb bBbbb bb B_

  19. F1 • all black (Bb) B B b Bb Bb b Bb Bb

  20. Parent generation (P) Black Labrador (BB) Brown Labrador (bb)

  21. Mendel’s First Law"Law of Segregation" • allele pairs separate during gametogenesis then randomly reform pairs at fertilization

  22. Dihybrid Cross • parental varieties differ in two characters characters: • seed color (Y) • seed shape (R)

  23. seed color alleles • yellow: dominant (YY, Yy) • green: recessive (yy) • seed shape alleles • round: dominant (RR, Rr) • wrinkled: recessive (rr)

  24. P1 • P: yellow/round X green/wrinkled • F1:dihybrid (YyRr) • F2 : offspring (9:3:3:1) 9 Y_R_ 3 Y_rr 3 yyR_ 1 yyrr F1 F2

  25. How do I know my Punnett is done correctly? all four are homozygous on both genes • look at the diagonals! all four are heterozygous on both genes (YyRr)

  26. Mendel’s Second Law"Law of Independent Assortment" • each allele pair assorts independently from one another during gamete formation

  27. Patterns of Inheritance not described by Mendel • still follow Mendel’s laws • Incomplete dominance • Codominance • Pleiotropy • Epistasis • Polygenic inheritance

  28. Incomplete Dominance • Blends are formed • examples: • Snapdragons • Tay-Sachs disease

  29. Snapdragon • Intermediate phenotype • Red = CRCR • Pink = CRCW • White = CWCW

  30. Codominance • Both alleles are expressed • examples: • Landsteiner blood groups • (A x B = AB) • shorthorn cattle • (white x red = roan) • calico cat • (orange-yellow x black)

  31. Blood groups: Codominance & multiple alleles http://health.stateuniversity.com/article_images/gem_01_img0116.jpg

  32. Blood type Test coagulates when it has the antibody for that type of blood same happens with the Rh group

  33. Blood Genotypes • IAIAhomozygous • IAi heterozygous • IBIB homozygous • IBi heterozygous • IAIB • ii • Rh group functions independently by complete dominance rules: • DD or Dd is Rh positive • dd is Rh negative Blood type A Blood type B Blood type AB Blood type O Examples : IAiDd A+ IBIBdd B- iiDD O+

  34. Class Activity • A X B = O is it possible? • What are the genotypes of the parents? • AB X O = O is it possible? • Give the genotypes of the possible children

  35. Shorthorn Cattle Codominance Red White Roan

  36. Calico Cat Codominance • B = black • R = red • XBXR • black XB • red XR • Barr body Barr body is an inactive strand of DNA

  37. Pleiotropy • single gene has multiple effects • example: in Siamese cats, one gene causes abnormal fur pigmentation and esophoria (crossed-eyed) • Waardenburg syndrome • white forelock • pale iris • deafness http://dermatology.cdlib.org/123/case_presentations/waardenburg/1.jpg

  38. Epistasis • one gene alters the expression of another that is independently inherited • example: albinism in animals (mice) • 9 B_ C_ = black • 3 B_ cc = albino • 3 bb C_ = brown • 1 bb cc = albino • 9:3:4 instead of 9:3:3:1

  39. Polygenic Inheritance • An additive effect of 2 or more genes on one character example • skin pigmentation • at least 3 genes • hair color • at least 4 genes

  40. Rule of Addition • The probability of an event that can occur in 2 or more different ways is the sum of the separate probabilities of those ways Rule of multiplication • Multiply individual probabilities to get overall probability

  41. Rules of Addition and Multiplication Female Male roll tongue (Rr) no roll tongue (rr) long eyelashes (Ll) short eyelashes (ll) cleft chin (Cc) cleft chin (Cc) Probability of having a • daughter 2/4 (xx, xx, xy, xy) • roll tongue 2/4 (Rr, Rr, rr, rr) • long eyelashes 2/4 (Ll, Ll, ll, ll) • cleft chin 3/4 (CC, Cc, Cc, cc) 2/4 x 2/4 x 2/4 x 3/4 = 24/256 = 9.375%

  42. Activity Eye color dark/light P_/pp Tongue rolling yes/no R_/rr small finger crooked/straight B_/bb widow's peak yes/no W_/ww hand clasping right/left C_/cc earlobe free/attached A_/aa Hitchhiker's thumb no/yes H_/hh PTC tasting yes/no D_/dd The End

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