Chapter ,9.5, 9.6

9.4 Homologous chromosomes bear the alleles for each character P P a a B b PP aa Bb Dominant allele Recessive allele Gene loci Homologous chromosomes Genotype: Heterozygous, with one dominant and one recessive allele Homozygous for the recessive allele Homozygous for the dominant allele

9.5 The law of independent assortment is revealed by tracking two characters at once What would happen if plants were crossed that differed in two characteristics. – Dihybrid cross Two monohybrid crosses occurring simultaneously. Would the characteristics assort independently or travel together?

9.5 The law of independent assortment is revealed by tracking two characters at once  Mendel performed the following dihybrid cross with the following results: P generation: round yellow seeds  wrinkled green seeds F 1 generation: all plants with round yellow seeds F 2 generation: – 9/16 had round yellow seeds – 3/16 had wrinkled yellow seeds – 3/16 had round green seeds – 1/16 had wrinkled green seeds © 2012 Pearson Education, Inc.

Figure 9.5A_1 F 1 generation P generation Gametes  RRYY rryy RY ry RrYy

9.5 The law of independent assortment is revealed by tracking two characters at once  Mendel needed to explain why the F 2 offspring had new nonparental combinations of traits and a 9:3:3:1 phenotypic ratio.  Mendel suggested that the inheritance of one character has no effect on the inheritance of another, called this the law of independent assortment. © 2012 Pearson Education, Inc.

9.5B In Labrador retrievers Black color (B) is dominant over chocolate (b) Normal vision (N) is dominant over Blindness by progressive retinal atrophy Cross two heterozygous Labs for each of these two traits. What are the genotypes of each dog? What are the possible gametes for each dog? What is the phenotypic ratio of this cross?

Predict the phenotypes of offspring obtained by mating a black lab homozygous for both coat color and normal eyes with a chocolate Lab that is blind from PRA What are the genotypes of each dog? What are the possible gametes for each dog? What are the genotypes of the offspring?

9.6 Geneticists can use the testcross to determine unknown genotypes  How would you determine the genotype of a black Lab of an unknown genotype?  What are the possible genotypes?  What would you do to determine the genotype of this dog? © 2012 Pearson Education, Inc.