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Observable Patterns of Inheritance

Observable Patterns of Inheritance. Edited by: R. LeBlanc, M.S. Mountain Pointe High School 2012. Starr/Taggart’s Biology: The Unity and Diversity of Life , 9e Chapter 11. Charles Barkley. Tom Cruise. What do Charles Barkley and Tom Cruise have in common? (hint: check out their ears).

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Observable Patterns of Inheritance

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  1. Observable Patterns of Inheritance Edited by: R. LeBlanc, M.S. Mountain Pointe High School 2012 Starr/Taggart’s Biology: The Unity and Diversity of Life, 9e Chapter 11

  2. Charles Barkley Tom Cruise What do Charles Barkley and Tom Cruise have in common? (hint: check out their ears). Gregor Mendel Joan Chen Fig. 11.1, p. 174

  3. Terms Used in Genetics • Genes • Alleles • Hybrid • Homozygous • Heterozygous • Dominant • Recessive • Genotype • Phenotype • Generations • P, F1, F2

  4. Plant Reproductive Organs

  5. Plant Reproductive Terms carpel stamen • GAMETES - the male or female sex cells. In plants, the sperm is the male sex cell (found in pollen grains), and the ovule (egg) is the female sex cell. • PISTIL – female reproductive structure. • STAMEN – male reproductive structure. • FERTILIZATION- the uniting of the male and female gametes within the flower. • POLLINATION - The transfer of pollen from the anther to the pistil, usually by wind, water, or insects. • CROSS-POLLINATION - transferring the pollen from one plant to another plant.

  6. Mendel identified seven traits in his garden peas that were easily studied: SEED SHAPE round wrinkled SEED COLOR yellow green POD SHAPE inflated wrinkled POD COLOR green yellow He carefully isolated pure breeding varieties before experimenting with crosses between different varieties. FLOWER COLOR purple white FLOWER POSITION axial terminal STEM LENGTH tall dwarf

  7. Mendel’s Insight Into Patterns of Inheritance • Mendel’s Experimental Approach • Garden pea plant Cross pollination What are the advantages of SELF cross pollination? What is the advantage of using pea plants? How did Mendel control his experiments?

  8. Mendel’s Experiment

  9. The Rule of Unit Factors • Mendel concluded that each organism has two factors (alleles) for each trait. • Heperformed crosses with seven different pairs of traits (for example, pure-breeding purple-flowered plants crossed with pure-breeding white-flowered plants). In every case he found that one trait disappeared from the F1 generation only to reappear in the F2 generation plants! • This is explained by the RuleofDominance which will be demonstrated in the next two examples:

  10. Mendel’s Theory of Segregation • Monohybrid cross • Gene segregation What do you notice about the alleles of both parents? What do the letters A & a stand for? (the font of the letters) What are diploid gamete cells? Haploid? Why are the final gamete cells haploids? What does the fertilized zygote traits represent? (check the alleles)

  11. Probability and Punnet Squares • A possibility of outcomes and crosses • Test crosses • Unknown genotype crossed with homozygous recessive

  12. Mendel’s Monohybrid Cross Pure White Flower Pure Purple Flower What traits (genotype) do F1 offspring have?

  13. Mendel’s Monohybrid Cross What percentage of the second generation are purple? White? What % are pure purple? White? If you planted four first generation seeds , how many of these seeds will be purple flowers in the 2nd generation?

  14. Section 1 Mendel’s Legacy Chapter 9 Mendel’s Conclusions

  15. Trait Studied Dominant Form Recessive Form F2 Dominant-to- Recessive Ratio SEED SHAPE 5,474 round 1,850 wrinkled 2.96:1 To get the ratios on the right to all be approximately equal, what do we know about the P1 plants? What do you notice about the number of plants studied? How did Mendel decide which of the traits were dominant? Recessive? Why aren’t the ratios exactly 3:1? SEED COLOR 6,022 yellow 2,001 green 3.01:1 POD SHAPE 882 inflated 299 wrinkled 2.95:1 POD COLOR 428 green 152 yellow 2.82:1 FLOWER COLOR 705 purple 224 white 3.15:1 FLOWER POSITION 651 long stem 207 at tip 3.14:1 Fig. 11.5, p. 178 STEM LENGTH 787 tall 277 dwarf 2.84:1

  16. Independent Assortment

  17. http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.htmlhttp://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html Use the website above for practice genetics problems. TRUE- BREEDING PARENTS: purple flowers, tall white flowers, dwarf x AABB aabb GAMETES: AB AB ab ab What are the phenotype ratios of all the offspring resulting from the cross of these 2 parents? Genotype? ALL F1 OFFSPRING: PURPLE TALL GENOTYPE: AaBb What about the phenotype ratio of the offspring of the F2 generation? 9 : 3 : 3: 1 AaBb F1 HYBRID OFFSPRING: In-text, p. 180

  18. X AABB purple- flowered tall parent (homozygous dominant) aabb white- flowered dwarf parent (homozygous recessive) ADDING UP THE F2 COMBINATIONS POSSIBLE: ab ab ab 9/16 or 9 purple-flowered, tall 3/16 or 3 purple-flowered, dwarf aB AB AB aB Ab AB Ab 3/16 or 3 white-flowered, tall 1/16 or 1 white-flowered, dwarf F1 OUTCOME: All F1 plants purple-flowered, tall (AaBb heterozygotes) AaBb AaBb meiosis, gamete formation 1/4 1/4 1/4 1/4 1/4 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb 1/4 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/4 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb 1/4 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb Fig. 11.9, p. 181 Possible outcomes of cross-fertilization

  19. Theory in Modern Form • Independent Assortment • Gametes require genes independently of how other pairs of genes were sorted out • Variety of Offspring

  20. INCOMPLETE DOMINANCE • A cross where one allele does not completely hide or mask the other producing a blended appearance in the phenotype. • Example: In snapdragons, pure red crossed with pure white produce pink!

  21. CODOMINANCE • Two non-identical alleles of a pair specify two different phenotypes yet one cannot mask the other and both are expressed .

  22. Multiple Alleles • More than two alleles in a population for a given trait. • Example: human blood types. • 3 alleles: A,B,O. • What do the letters A, B & O stand for? • A & B stand for a type of protein found on the surface of RBC and i stands for the lack of this protein.

  23. Multiple Effects of Single Genes • Pleiotropy. • The expression of a single gene can influence two or more traits. • Sickle Cell Anemia. • What do you notice about the physical effects of having sickle cell anemia? *Refer to the next slide

  24. HbA = Normal Red Blood Cells HbS = Sickle Cell Red Blood Cells To develop the full effects of Sickle Cell Anemia you need to be Homozygous for this trait. Fig. 11.12, p. 183

  25. Interactions Between Gene Pairs • Epistasis • Fur color in mammals • Melanin production • Albinism • Comb shape in chickens (see the example in the next slides) (When 1 gene pair influences other gene pairs with their combined activities producing some effect on phenotype) (Melanin produces fur color) (influenced by an enzyme produced from the alleles from another gene) (the absence of melanin)

  26. Epistasis Problem: Cross a Rose Comb (RRpp) chicken with a Pea (rrPP) Comb chicken. What will be the phenotype ratio of the off-spring? Cross this F1 generation. (R = Rose Comb; P = Pea Comb; RP = Walnut Comb; and rp = Single Comb) comb P: RRpp (rose comb) rrPP (pea comb) F1: RrPp (all walnut comb) X X F2: 9/16 walnut (RRPP, RRPp, RrPP, or RrPp) 3/16 rose (RRpp or Rrpp) 3/16 pea (rrPP or rrPp) 1/16 single (rrpp) WALNUT COMB ROSE COMB PEA COMB SINGLE COMB NOTE: Sometimes interaction between 2 gene pairs results in a phenotype that neither pair can produce alone. Comb shape in chickens can result in 4 types depending on the interactions of 2 gene pairs (R & P) Fig. 11.15, p. 185

  27. What causes this Albino snake?????? In some individuals the 2 genes mentioned earlier do NOT interact, causing another gene to effect coloration. At gene ‘C’, a gene at another gene locus, is responsible for the enzyme called tyrosinase, one of many enzymes responsible for the production of melanin. An individual with one of the dominant alleles (CC or Cc) can make the functional enzyme. If two recessive alleles (cc) are present, melanin production is interfered with resulting in ALBINISM. Fig. 11.14, p. 185

  28. Epistasis Problem: Cross homozygous Black Lab with a Gold Lab (bbee) What would be the off-springs phenotype ratio of a cross between 2 F1 generation off-spring? List the different genotypes of each phenotype represented? B = BLACK b = BROWN E = Full deposit ee = Reduced Deposit produces a Golden color (in B or b) Black Golden Brown The alleles of one gene specify an enzyme for melanin production while an allele on another gene is responsible for the deposit of melanin in the hairs of the organism. (BBEE; BBEe; BbEE; BbEe) (bbEE; bbEe) (BBee; Bbee; bbee)

  29. Less Predictable Variation in Traits • Camptodactyly (A rare genetic abnormality the affects both the shape and the movement of fingers. This can be caused by improper enzyme production.) • Continuous variation (A range of small differences in the phenotypes of individuals) • Eye color • Height

  30. Eye Color: • iris (eye color) is beneath the cornea. • Color: a cumulative outcome of a number of gene products • Melanin production affects color. • Dark eyes = increased amounts of melanin. • Brown eyes = less melanin. • Light brown/hazel = even less • Gray/green/blue = very little melanin, so these wave lengths of light are reflected back to the observer. • Continuous Variation: • Different pairs of genes (alleles) interact to produce and deposit melanin. • Eye color seems to be Continuous; from • Black ------------- Blue • (+ melanin - melanin) Fig. 11.16, p. 186

  31. Examples of Environmental Effects on Phenotypes • Himalayan Rabbit & Siamese Cat • Less melanin in warm body regions. Heat makes enzyme in melanin production pathway less active • Hydrangea color • Color ranges from blue to pink, depending on acidity of soil

  32. In Conclusion • Gene is unit of information about a heritable trait • Mendel provided indirect evidence of dominant and recessive genes • F1 offspring form monohybrid crosses • AA x aa -----> Aa • Crosses from F1 result in F2 offspring with phenotypes having a 3:1 ratio

  33. In Conclusion • Theory of segregation states that genes of each pair segregate during meiosis and wind up in different gametes • Dihybrid crosses result in 9:3:3:1 phenotypic ratio • Theory of Independent Assortment states that gene pairs independently sort out into different gametes regardless of other gene pairs of other chromosomes

  34. In Conclusion • Four factors influence gene expression • Degrees of dominance • Products of pairs of genes may interact • One gene may effect two or more traits • Environment

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