For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop.

Using RB1⁺ for the normal wild-type allele and RB1⁻ for the mutant allele, identify the genotype of a cell in a retinoblastoma tumor.

For parts (a), (b), and (c) of this problem, draw a diagram illustrating the alleles on homologous chromosomes for the genotypes given, assuming in each case that the genes reside on the chromosome in the order written. For parts (d) and (e), give the information requested.

AB/ab

Reciprocal crosses of experimental animals or plants sometimes give different results in the . What are two possible genetic explanations? How would you distinguish between these two possibilities (i.e., what crosses would you perform, and what would the results tell you)?

For the retinal cancer retinoblastoma, the inheritance of one mutated copy of RB1 from one of the parents is often referred to as a mutation that produces a 'dominant predisposition to cancer.' This means that the first mutation does not produce cancer but makes it very likely that cancer will develop.

What is the genotype of a normal cell in the retina in a person who has sporadic retinoblastoma? What is the normal cell genotype if the person has hereditary retinoblastoma? Explain the reason for the difference between the genotypes.

An organism has alleles R₁ and R₂ on one pair of homologous chromosomes, and it has alleles  T₁ and T₂  on another pair. Diagram these pairs of homologs at the end of metaphase I, the end of telophase I, and the end of telophase II, and show how meiosis in this organism produces gametes in expected Mendelian proportions. Assume no crossover between homologous chromosomes.