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Biology I - GENETICS 1-12 Novak Gregor Mendel 1822-1884 MENDEL’S PRINCIPLES I. ALLELES • Any organism has two units of heredity (genes) for each trait in every body cell II. SEGREGATION • The two units (genes) for a trait are separated in the cell; one gene is found on a chromosome while the other is located in the same place on its partner (homologous) chromosome III. DOMINANCE • • A. When two genes of a trait are different in the cells of the organism, the gene that shows up is the dominant while the gene that remains hidden is the recessive B. Combinations of the two genes (genotypes) 1. Homozygous (pure) dominant - both genes are dominant 2. Homozygous (pure) recessive - both genes are recessive 3. Heterozygous (hybrid) - one gene is dominant & the other is recessive IV. RECOMBINATION (INDEPENDENT ASSORTMENT) • In each new generation there is a complete new rearrangement of the units of heredity (genes) Following the Generations Cross 2 Pure Plants TT x tt Results in all Hybrids Tt Cross 2 Hybrids get 3 Tall & 1 Short TT, Tt, tt Generation “Gap” • Parental P1 Generation = the parental generation in a breeding experiment. • F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation) – From breeding individuals from the P1 generation • F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation) – From breeding individuals from the F1 generation Mendel’s Experimental Results Thomas Hunt Morgan 1866-1945 Incomplete Dominance (blending inheritance) • INCOMPLETE DOMINANCE • A condition in which both alleles for a characteristic are partially expressed Incomplete Dominance • F1 hybrids have an appearance somewhat in between or a blend of the phenotypes of the two parental varieties. • Example: snapdragons (flower) • red (RR) x white (WW) • • R R = red flower W = white flower W W R Incomplete Dominance R R W RW RW produces the F1 generation W RW RW All RW = pink (heterozygous pink) Incomplete Dominance • CODOMINANCE • A condition in which both alleles for a characteristic are fully expressed Codominant white and pink Codominant white and pink Homozygous Red Hereford Red Homozygous white Roan hybrid Roan hybrid Codominant cross Sex-Linked Inheritance Color Blindness TYPES OF COLOR BLINDNESS normal - trichromatic color vision protanopia red-green blindness (no red cones) deutanopia red-green blindness (no green cones) tritanopia blue-yellow blindness (no blue cones) typical achromatopsia (no cones; rod monochromat) protanomaly (anomalous red cones) deutanomaly (anomalous green cones) tritanomaly (anomalous blue cones) atypical achromatopsia (low cones; cone monochromat) Red Green Color Blindness Male1.01% Female0.02% Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome Hemophilia Female Carriers The effects of hemophilia Human Blood Coagulation Cascade DIHYBRID INHERITANCE Pea Plants Height Seed Color Tall = TT, Tt Short = tt Yellow = YY, Yy Green = yy Let’s cross a homozygous tall (TT), homozygous yellow seed (YY) plant with a short (tt), green seed (yy) plant. TTYY x ttyy These are the genotypes of the two plants. Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). First T TTYY with first Y TY Gamete 1 = sperm, egg, pollen . . . Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). First T TTYY TY TY Gamete 1 Gamete 2 with second Y Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). Second T TTYY TY TY Gamete 1 Gamete 2 with first Y TY Gamete 3 Independent Assortment Mendels’ principle of Independent Assortment states that genes for different traits can segregate independently during the formation of gametes (eggs & sperm in animals, eggs and pollen in plants). Second T TTYY TY TY Gamete 1 Gamete 2 with second Y TY TY Gamete 3 Gamete 4 Dihybrid Punnett Square - F1 P1 = TTYY TY TY TY ty ty P2 = ttyy ty ty Will be F1 Generation TY Dihybrid Punnett Square - F1 TY ty TTYy ty TTYy ty TTYy ty TTYy TY TY TY Dihybrid Punnett Square - F1 TY TY TY TY ty TtYy TtYy TtYy TtYy ty TTYY TtYY TtYY TTYY ty TTYY TTYY TTYY TTYY ty TTYY TTYY TTYY TTYY Dihybrid Punnett Square - F1 TY TY TY TY ty TtYy TtYy TtYy TtYy ty TtYy TtYy TtYy TtYy ty TtYy TtYy TtYy TtYy ty TtYy TtYy TtYy TtYy Dihybrid Punnett Square - F1 TY ty ty ty ty TY TY TY Genotype ratio: TtYy TtYy TtYy TtYy - 16/16 TtYy TtYy TtYy TtYy Phenotype ratio: TtYy TtYy TtYy Tall, Yellow - 16/16 TtYy TtYy TtYy TtYy TtYy TtYy Dihybrid Punnett Square – F2 We need to pair up the genes which can be given to each gamete (egg and pollen). Let’s cross two of the plants from the F1 generation ty We need to TYthe TY TY pair up genes TtYy TtYy TtYy TtYy ty TtYy TtYy x TtYy TtYy ty TtYy TtYy t Y TtYy t y TtYy ty TtYy TtYy TtYy TtYy . TY Ty TY Dihybrid Punnett Square F2 TY Ty tY ty TY Ty tY ty Both the plants can give the same gene combinations to their gametes, so the pairs along the top and down the side are the same. Dihybrid Punnett Square – F2 When you pair up the gametes from the two plants, always put like letters together and within the like letters, put the CAPITAL letter in front of the lowercase letter. Dihybrid Punnett Square F2 TY Ty tY ty TY TTYY TTYy TtYY TtYy Ty ???? ???? ???? ???? tY ???? ???? ???? ???? ty ???? ???? ???? ???? Your Turn!! Dihybrid Punnett Square F2 TY Ty tY ty TY TTYY TTYy TtYY TtYy Ty TTYy tY TTyy TtYy Ttyy F2 generation TtYY TtYy ttYY ttYy ty TtYy Ttyy ttYy ttyy Dihybrid Punnett Square F2 Genotype and phenotype ratios? TY Ty tY ty TY TTYY TTYy TtYY TtYy Ty TTYy TTyy TtYy Ttyy tY TtYY TtYy ttYY ttYy ty TtYy Ttyy ttYy ttyy F2 Genotype Ratio TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 TTyy - 1 Ttyy - 2 ttYY - 1 ttYy - 2 ttyy - 1 F2 Phenotype Ratio TTYY - 1 TTYy - 2 TtYY - 2 TtYy - 4 TTyy - 1 Ttyy - 2 ttYY - 1 ttYy - 2 ttyy - 1 Tall, Yellow - 9 Tall, Green - 3 Short, Yellow - 3 Short, Green - 1 Another Mendelian Dihybrid Problem Dihybrid F2 Results Dihybrid F2 Results •The End
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