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Genetic Crosses

Genetic Crosses. Section 9.2. 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 ). Phenotype.

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Genetic Crosses

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  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)

  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

  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)

  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_____________ number of opportunities for an event to happen

  8. Example: yellow pea seeds appeared 6022 times and green pea seeds appeared 2001 times in the F2 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 ) 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 (pp) p p purple flower (PP) P Pp Pp P Pp Pp

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

  13. Heterozygous X Heterozygous black coat (Bb) B b black coat (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 = pink rr = white

  16. Incomplete Dominance in Four O’clock Flowers Pink flower (Rr) R r Pink flower (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

  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 (rryy) ry ry ry ry round & RY RrYyRrYy RrYy RrYy yellow RY RrYy RrYy RrYy RrYy (RRYY) RY RrYy RrYy RrYy RrYy Ry RrYy RrYy RrYy RrYy

  20. Heterozygous X Heterozygous round & yellow (RrYy) 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

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

  22. STUDY! • STUDY! STUDY! STUDY! STUDY! • STUDY! STUDY! STUDY! STUDY! • STUDY! STUDY! STUDY! STUDY! • STUDY! STUDY! STUDY! STUDY! • STUDY! STUDY! STUDY! STUDY!

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