1. Genetic Crosses Section 9.2

2. Genotype  The genetic makeup of an organism  Consists of the alleles that the organism inherits from its parents  Example: white flowering pea plants (recessive trait pp) (recessive trait pp)

3. Phenotype  The appearance of an organism as a result of its genotype  Example: pea plants that are PP or Pp will have purple flowers will have purple flowers

4. Homozygous  Both alleles of a pair are alike  May be homozygous dominant (PP) or homozygous recessive (pp)

5. Heterozygous  The two alleles in the pair are different  Example: a pea plant that is heterozygous for flower color would be Pp (purple flowers) would be Pp (purple flowers)

6. Probability  The likelihood that a specific event will occur  May be expressed as a decimal, a percentage, or a fraction

7.  Probability = number of times an event is expected to happen_____________ expected to happen_____________ number of opportunities for an event number of opportunities for an event to happen to happen

8. Example: yellow pea seeds appeared 6022 times and green pea seeds appeared 2001 times in the F 2 green pea seeds appeared 2001 times in the F 2 Total (6022 + 2001 = 8023) Total (6022 + 2001 = 8023) What is the probability that the dominant trait will appear in a similar cross? P = 6022 =.75 (or 75% or ¾ ) P = 6022 =.75 (or 75% or ¾ ) 8023 8023

9. Monohybrid Cross  A cross between individuals that involves one pair of contrasting traits  Example: crossing a pea plant that is pure for white flowers (pp) with one that is pure for purple flowers (PP)

10. Punnett Square  Diagram used to predict the outcome of certain crosses  Predicts the probability of inherited traits

11. Homozygous X Homozygous white flower white flower (pp) (pp) p p p ppurple flower (PP) P Pp Pp P Pp Pp P Pp Pp

12. Homozygous X Heterozygous black coat black coat (Bb) (Bb) B b B b black coat (BB) B BB Bb (BB) B BB Bb B BB Bb B BB Bb

13. Heterozygous X Heterozygous black coat black coat (Bb) (Bb) B b B b black coat (Bb) B BB Bb (Bb) B BB Bb b Bb bb b Bb bb

14. Testcross  An individual of an unknown genotype is crossed with a homozygous recessive individual  Can be used to determine the genotype of any individual whose phenotype is dominant (example: BB or Bb)

15. Incomplete Dominance  Occurs when two or more alleles influence the phenotype  Example: four o’clock flowers RR = red RR = red Rr = pink Rr = pink rr = white rr = white

16. Incomplete Dominance in Four O’clock Flowers Pink flower Pink flower (Rr) (Rr) R r R r Pink flower (Rr) R RR Rr (Rr) R RR Rr r Rr rr r Rr rr Phenotypic ratio: 1 red: 2 pink:1 white

17. Codominance  Occurs when both alleles for a gene are expressed in a heterozygous offspring  Neither allele is dominant or recessive  Example: roan horses R = red coat (RR`) R` = white (RR`) R` = white

18. Dihybrid Cross  A cross between individuals that involves two pairs of contrasting traits  Must consider how the four alleles from each parent can combine

19. Homozygous X Homozygous wrinkled & green wrinkled & green (rryy) (rryy) ry ry ry ry ry ry ry ry round & RY RrYy RrYy RrYy RrYy yellow RY RrYy RrYy RrYy RrYy (RRYY) RY RrYy RrYy RrYy RrYy Ry RrYy RrYy RrYy RrYy Ry RrYy RrYy RrYy RrYy

20. Heterozygous X Heterozygous round & yellow round & yellow (RrYy) (RrYy) RY Ry rY ry RY Ry rY ry round & RY RRYY RRYy RrYY RrYy yellow Ry RRYy RRyy RrYy Rryy (RrYy) rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy ry RrYy Rryy rrYy rryy

21. Four Phenotypes 9/16 round & yellow 9/16 round & yellow (genotypes RRYY, RRYy, RrYY, and RrYy) (genotypes RRYY, RRYy, RrYY, and RrYy) 3/16 round & green 3/16 round & green (genotypes RRyy and Rryy) (genotypes RRyy and Rryy) 3/16 wrinkled & yellow 3/16 wrinkled & yellow (genotypes rrYY and rrYy) (genotypes rrYY and rrYy) 1/16 wrinkled & green 1/16 wrinkled & green (genotype rryy) (genotype rryy)

22. STUDY! STUDY!  STUDY! STUDY! STUDY! STUDY!