Question

9. (8 pts) Dr. Zhivag orking in a lab and identified three genes in a rat. He m ated O Was long tail (L), short hair (S), brown (B) rats that are heterozygous for all three traits with short tail (l), long hair (s), white (b) rats that are homozygous for all three traits. The following numbers and types of offspring were obtained from this cross Phenotype Number long tailed, long hair, white 250 short tailed, short hair, brown 275 long tailed, short hair, brown 95 short tailed, long hair, white 98 long tailed, short hair, white 115 short tailed, long hair, brown 125 long tailed, long hair, brown 23 short tailed, short hair, white 19 Total 1000 a. Are the genes completely linked i completely linked pr unlinked? b. Give the correct gene order for these three genes. Calculate the map distances between these three genes and draw a genetic map indicating these distances. Please show ALL calculations for full credit. 23 S mu 28,2 min

I went ahead and put the question up with the answers. These are my professor's answers so they should be correct. Can you please explain how to get these answers. I don't understand the difference between "Completely Linked," "Incompletely Linked," and "Unlinked." Thanks!

Answer 1

1. Since this trihybrid cross does not follow the normal medalian law ( law of independent assortment), they are giving the ratio other than the mendalian ratio i.e. 27:9:9:9:3:3:3:1, so it can be said that these three genes are incompletely linked. If they give the ratio like mendalian ratio, they are said to be unlinked genes.