Question

nvision in a family the mother has breast cancer and retinoblastoma (both conferred by recessive alleles on chromosome 17, and the two loci are on the same arm of this chromosome and 3 centimorgans apart), while the father does not carry any of these recessive alleles. What is the probability of their daughter having both cancers

Answer 1

0%

Step-by-step explanation:

Two genes/loci are linked when they are located on the same chromosome. Recombination, also known as crossing over, refers to the exchange of genetic material between non-sister chromatids during meiosis. One centimorgan (1 cM) is a genetic measurement of the distance between two loci on the same chromosome in which 1% crossing over occurs. In this case, the mother is an unaffected carrier who has one copy of both linked mutations (i.e., of both breast cancer and retinoblastoma mutations), thereby the expected frequency of recombination in the female meiosis is 3% (3 cM). Moreover, and since the father is an unaffected individual (who does not carry any of these recessive alleles) and both breast cancer and retinoblastoma conditions are caused by recessive somatic mutations, the probability of their daughter having both cancers is 0%, (offspring always receive one copy of each autosomal/somatic chromosome from the mother and one copy from the father).