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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, Chapter 11 9e Tom Cruise Charles Barkley What do Charles Barkley and Tom Cruise have in common? (hint: check out their ears). Gregor Mendel Joan Chen Fig. 11.1, p. 174 Terms Used in Genetics Genes Alleles Hybrid Homozygous Heterozygous Dominant Recessive Genotype Phenotype Generations P, F1, F2 Plant Reproductive Organs 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. 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 FLOWER COLOR purple white FLOWER POSITION axial terminal STEM LENGTH tall dwarf He carefully isolated pure breeding varieties before experimenting with crosses between different varieties. 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? Mendel’s Experiment Mendel concluded that each organism has two factors (alleles) for each trait. He performed 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 Rule of Dominance which will be demonstrated in the next two examples: 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) Probability and Punnet Squares A possibility of outcomes and crosses Test crosses Unknown genotype crossed with homozygous recessive Mendel’s Monohybrid Cross Pure White Flower Pure Purple Flower What traits (genotype) do F1 offspring have? 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? Chapter 9 Section 1 Mendel’s Legacy Mendel’s Conclusions Trait Studied SEED SHAPE Dominant Form Recessive Form F2 Dominant-toRecessive Ratio 5,474 round 1,850 wrinkled 2.96:1 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 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? STEM LENGTH 787 tall 277 dwarf 2.84:1 Fig. 11.5, p. 178 Independent Assortment http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html Use the website above for practice genetics problems. TRUEBREEDING PARENTS: purple flowers, tall x white flowers, dwarf AABB GAMETES: AB aabb AB ab AaBb F1 HYBRID OFFSPRING: 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 In-text, p. 180 AABB purpleflowered tall parent (homozygous dominant) AB aabb whiteflowered dwarf parent (homozygous recessive) ab X F1 OUTCOME: All F1 plants purple-flowered, tall (AaBb heterozygotes) AaBb AaBb meiosis, gamete formation 1/4 AB 1/4 Ab 1/4 aB 1/4 ab 1/4 AB 1/4 Ab 1/4 aB 1/4 ab ADDING UP THE F2 COMBINATIONS POSSIBLE: 1/16 1/16 1/16 1/16 9/16 or 9 purple-flowered, tall AABB AABb AaBB AaBb 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/16 1/16 1/16 3/16 or 3 purple-flowered, dwarf 3/16 or 3 white-flowered, tall 1/16 or 1 white-flowered, dwarf 1/16 AaBB AaBb aaBB aaBb 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb Possible outcomes of cross-fertilization Fig. 11.9, p. 181 Theory in Modern Form Independent Assortment Gametes require genes independently of how other pairs of genes were sorted out Variety of Offspring 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! CODOMINANCE Two non-identical alleles of a pair specify two different phenotypes yet one cannot mask the other and both are expressed . 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. 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 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 Interactions Between Gene Pairs Epistasis (When 1 gene pair influences other gene pairs with their combined activities producing some effect on phenotype) Fur color in mammals (Melanin produces fur color) Melanin production (influenced by an enzyme produced from the alleles from another gene) Albinism (the absence of melanin) Comb shape in chickens (see the example in the next slides) 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) P: RRpp (rose comb) X rrPP (pea comb) F1: RrPp (all walnut comb) 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) ROSE COMB PEA COMB SINGLE COMB comb WALNUT 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 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 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 offspring? List the different genotypes of each phenotype represented? Black Golden Brown B = BLACK b = BROWN E = Full deposit ee = Reduced Deposit produces a Golden color (in B or b) 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) 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 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. Continuous Variation: -Different pairs of genes (alleles) interact to produce and deposit melanin. -Eye color seems to be Continuous; from Black ------------- Blue (+ melanin - 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. Fig. 11.16, p. 186 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 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 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 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