1. 9-2: Genetic Crosses Help to predict the genetic makeup + appearance of offspring

2. Genotype & Phenotype Genotype – genetic makeup of an organism Genotype – genetic makeup of an organism –Consists of alleles inherited from parents –Ex. PP or Pp = purple flower; pp = white flower Phenotype – the appearance of an organism as a result of its genotype Phenotype – the appearance of an organism as a result of its genotype –Ex. PP or Pp = purple flower; pp = white flower

3. More words to know… Homozygous – both alleles in a pair are alike Homozygous – both alleles in a pair are alike –Also known as a PUREBRED –Homozygous dominant = PP –Homozygous recessive = pp Heterozygous – alleles are different Heterozygous – alleles are different –Also known as a HYBRID –Heterozygous = P p

4. Probability The likelihood that a specific event will occur The likelihood that a specific event will occur –May be expressed as a decimal, percentage, fraction, or ratio –Equation:  # times an event is expected to happen # opportunities for it to happen

5. Probability (cont) Examples: Examples: –Mendel observed that yellow seed color in F 2 appeared 6,022 times and green seed color appeared 2,001 times  Total number of seeds = 8,023 –Probability of dominant trait appearing  6,022/8,023 =.75, 75%, or ¾ –Probability of recessive trait appearing  2,001/8,023 =.25, 25%, or ¼

6. Probability (cont) What does probability tell us about the offspring of 2 heterozygous individuals? What does probability tell us about the offspring of 2 heterozygous individuals? –There are 3 out of 4 chances the offspring will have the dominant trait –There is 1 out of 4 chances the offspring will have the recessive trait *The results of probability are more likely to occur if you have more trials* *The results of probability are more likely to occur if you have more trials*

7. Probability (cont) Ex. Flipping a coin Ex. Flipping a coin What is the probability a coin will land on heads? What is the probability a coin will land on heads? –50% What is the probability a coin will land on tails? What is the probability a coin will land on tails? –50%

8. Monohybrid Crosses A cross between individuals involving one pair of contrasting traits is called a monohybrid cross A cross between individuals involving one pair of contrasting traits is called a monohybrid cross –There are 4 possible outcomes (2 2 ) Results are created with the use of Punnett Square Results are created with the use of Punnett Square –A diagram that helps biologist predict the probability that certain traits will be inherited by offspring

9. Example 1: Homozygous (Dominant) x Homozygous (recessive) P – purple flower; p – white flower P – purple flower; p – white flower Cross = PP x pp Cross = PP x pp Genotypes = 4 P p Genotypes = 4 P p Phenotypes = 4 purple flowers Phenotypes = 4 purple flowers PpPpPpPp PpPpPpPp PpPpPpPp PpPpPpPp PP p p

10. Example 2a: Homozygous (Dominant) x Heterozygous B – coat; b – brown coat B – black coat; b – brown coat Cross = BB x Bb Cross = BB x Bb Genotypes = 2 BB, 2Bb Genotypes = 2 BB, 2Bb Phenotypes = 4 coat Phenotypes = 4 black coat BBBb BBBb

11. Example 2b: Homozygous (recessive) x Heterozygous B – coat; b – brown coat B – black coat; b – brown coat Cross = bb x Bb Cross = bb x Bb Genotypes = 2 bb, 2 Bb Genotypes = 2 bb, 2 Bb Phenotypes = 2 brown coat, 2 coat Phenotypes = 2 brown coat, 2 black coat Bb bb Bbbb b b Bb

12. Example 3: Heterozygous x Heterozygous B – coat; b – brown coat B – black coat; b – brown coat Cross = Bb x Bb Cross = Bb x Bb Genotypes = 1 BB, 2Bb, 1bb Genotypes = 1 BB, 2Bb, 1bb Phenotypes = 3, 1 brown Phenotypes = 3 black, 1 brown BBBb bb b B Bb

13. Gentoypic vs. Phenotypic Ratio Genotypic ratio for the last cross Genotypic ratio for the last cross –1BB : 2Bb : 1bb Phenotypic ratio for the last cross Phenotypic ratio for the last cross –3 :1 brown –3 black :1 brown

14. Example #4: Testcross A is used to find an unknown genotype A testcross is used to find an unknown genotype –Can help determine genotype of any individual whose phenotype is dominant –cross individual w/ homozygous recessive –Examples:

15. Complete vs. Incomplete Dominance Complete dominance –When one allele is completely dominant over the other  Ex. B b Incomplete dominance Incomplete dominance –No dominant or recessive allele; a heterozygous individual has an intermediate phenotype  Ex. B b

16. Example #5: Incomplete Dominance Japanese 4 o’clock flowers (snapdragons) Japanese 4 o’clock flowers (snapdragons) –R = red –r = white Cross: RR x rr Cross: RR x rr Genotypes: 4 Rr Genotypes: 4 Rr Phenotypes: 4 pink flowers Phenotypes: 4 pink flowers Rr

18. Cross: Rr x Rr Cross: Rr x Rr What is the probable genotypic ratio? What is the probable genotypic ratio? –1 RR : 2 Rr : 1 rr What is the probable phenotypic ratio? What is the probable phenotypic ratio? –1 Red : 2 Pink : 1 white Cross 2 heterozygous flowers RRRr rr

20. CODOMINANCE When both alleles are dominant and influence the phenotype of the individual When both alleles are dominant and influence the phenotype of the individual –Ex. Blood type AB A A BB

21. Dihybrid Crosses A dihybrid cross involves crossing 2 contrasting traits A dihybrid cross involves crossing 2 contrasting traits –There are 16 possible outcomes (2 4 ) –Punnett square:

22. Example #1: Homozygous Dominant x Homozygous Recessive R = round seeds R = round seeds r = wrinkled seeds r = wrinkled seeds Y = yellow seed color Y = yellow seed color y = green seed color y = green seed color Cross = RRYY x rryy Cross = RRYY x rryy How do we determine the alleles given off by each parent? How do we determine the alleles given off by each parent? –The “ FOIL” method!!!

23. FOIL (First-Outer-Inner-Last) Parent 1 RRYY Parent 1 RRYY Alleles : RY,RY,RY,RY Alleles : RY,RY,RY,RY

24. FOIL (First-Outer-Inner-Last) Parent 2 rryy Parent 2 rryy Alleles: ry,ry,ry,ry Alleles: ry,ry,ry,ry

25. Genotypes: 16 RrYyGenotypes: 16 RrYy Phenotypes: 16 round, yellowPhenotypes: 16 round, yellow RrYy ry RY

27. Heterozygous x Heterozygous Cross: RrYy x RrYy Cross: RrYy x RrYy Alleles from each parent: Alleles from each parent: –Parent 1 = RY, Ry, rY, ry –Parent 2 = RY, Ry, rY, ry

28. RrYy x RrYy RRYYRRYyRrYYRrYy RRYyRRyyRrYyRryy RrYYRrYyrrYYrrYy RrYyRryyrrYyrryy RYRyrYry RY Ry rY ry

29. Results of the cross Genotypes – Genotypes – –1 RRYY, 2RRYy, 1 RRyy, 2 RrYY, 4 RrYy, 2 Rryy, 1 rrYY, 2 rrYy, 1 rryy Phenoytpes – Phenoytpes – –9 round, yellow; 3 round, green; 3 wrinkled, yellow; 1 wrinkled, green

31. Multiple Alleles + Polygenic Traits Multiple Alleles – 3 or more alleles Multiple Alleles – 3 or more alleles –Blood types  A, B, O Polygenic – 2 or more genes Polygenic – 2 or more genes –Height –Weight –Eye color –Intelligence –Skin color