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Dihybrid Crosses

Dihybrid Crosses. Genetics Continued. Law of Segregation. During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.

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Dihybrid Crosses

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  1. Dihybrid Crosses Genetics Continued

  2. Law of Segregation • During the formationofgametes(eggs or sperm), the two alleles responsible for a trait separate from each other. • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

  3. Applying the Law of Segregation

  4. Law of Independent Assortment • Alleles for different traits are distributed to sex cells (& offspring) independently of one another. • This law can be illustrated using dihybrid crosses.

  5. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s “Law of Independent Assortment” • a. Each pair of alleles segregates independently during gamete formation • b. Formula: 2n (n = # of heterozygotes)

  6. Remember: 2n (n = # of heterozygotes) 1. RrYy 2. AaBbCCDd 3. MmNnOoPPQQRrssTtQq Question:How many gametes will be produced for the following allele arrangements?

  7. Answer 1. RrYy: 2n = 22 = 4 gametes RY RyrYry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCdAbCDAbCd aBCDaBCdabCDabCD MmNnOoPPQQRrssTtQq: 2n= 26 = 64 gametes

  8. Dihybrid Cross • Traits: Seed shape &Seed color • Alleles:(R)round, (r)wrinkled(Y)yellow, (y) green • Cross: RrYy x RrYy **use FOIL** RY, Ry, rY, ry RY, Ry, rY, ry All possible gamete combinations

  9. RY Ry rY ry RY Ry rY ry Dihybrid Cross

  10. RY Ry rY ry RY Ry rY ry Dihybrid Cross : 1 RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy RrYY RrYy rrYY rrYy RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio

  11. Dyhybrid Analysis • Genotypes: • Genotypic Ratios: • Phenotypes: Round/Yellow : Round/green : wrinkled/Yellow : wrinkled/green • Phenotypic Ratios: 9 : 3 : 3 : 1

  12. Dihybrid Cross Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1 9:3:3:1

  13. bC b___ bc Test Cross • A mating between an individual of unknown genotype and a homozygous recessive individual. • Example:bbC__ x bbcc • BB = brown eyes • Bb = brown eyes • bb = blue eyes • CC = curly hair • Cc = curly hair • cc = straight hair

  14. bC b___ C bC b___ c bc bbCc bbCc or bc bbCc bbcc Test Cross • Possible results:

  15. LAW PARENT CROSS OFFSPRING DOMINANCE TT x tttall x short 100% Tt tall SEGREGATION Tt x Tttall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGground & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods Summary of Mendel’s laws

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