University:
High School
Course:
High School Genetics
Academic year:

2023
Views:

495

Pages:

9
Author:

5CelestialChronicle

Punnett Squares a visual graph used to calculate the probability (chance) of passing a trait on to offspring The 4 monohybrid crosses. Essential Questions 1. What is the genotype ratio when we have a cross between purebred recessive and purebred dominant parents? 2. What is the phenotype ratio when we cross two hybrids together? 3. When we do a test cross, what do we always cross with? 1. Purebred Dominant x Purebred Recessive (PP x pp) • Genotype Ratio: 4/4 Pp • Phenotype Ratio: 4/4 Dominant 2. Purebred Dominant x Hybrid (BB X Bb) • Genotype Ratio: 2/4 BB: 2/4 Bb 1BB:1Bb 50%BB:50%Bb • Phenotype Ratio: 4/4 Dominant 3. Hybrid x Hybrid (Bb x Bb) • Genotype Ratio: ¼ BB: 2/4 Bb: ¼ bb 1BB:2Bb:1bb 25%BB:50%Bb:25%bb • Phenotype Ratio: 3/4Dominant: 1/4Recessive 4.) Hybrid x Purebred recessive Bb x bb Genotype Ratio 2/4Bb:2/4bb Phenotype Ratio 2/4 Dominant: 2/4 Recessive Testcross • Determines the genotype of an individual whose genotype is unknown – To perform a test cross, you cross the individual with an unknown genotype with a homozygous recessive individual – The resulting offspring can reveal the unknown allele Example: Testcross In guinea pigs, black coats are dominant over brown coats. How would you determine the genotype of a guinea pig with a black coat? Perform a testcross! Alleles: B = black Trait: Coat color b = brown Possible Genotypes for test subject: BB or Bb Possibility 1: BB x bb Possibility 2: Bb x bb B B b Bb Bb b Bb Bb What this tells us: If none of the offspring have brown coats, the B b b Bb bb b Bb bb What this tells us: If any of the offspring have brown coats, the Summary of the 4 crosses Cross Genotype Ratio BB x bb All Bb BB x Bb Bb x Bb Bb x bb 2BB:2Bb Phenotype Ratio All Dominant All Dominant 1BB:2Bb:1bb 3 Dominant: 1 Recessive 2Bb:2bb 2 Dominant: 2 Recessive