Can someone please explain these concepts to me and the answ

Can someone please explain these concepts to me and the answers? I have an exam coming up and am still very confused..

Suppose you identified two new mutations in Spartan fruit flies (Drosophila spartanensis). One mutation, \'blue body\' results in the entire body being bright blue, whereas the body color of wildtype flies is tan. A second mutation, black wings, shows very dark wings, whereas the wings of wildtype flies are clear. Let\'s also say that you were able to culture true-breeding populations of both mutations and then you tested the inheritance of each by performing a set of reciprocal crosses with true-breeding flies. Below are the F1 and F2 progeny of these crosses: Offspring Offspring F1 Generation F3 Generation Parental Crosses Phenotype Males Females Total Combinations Males Females Tota Tan & Clear 27 25 52 Tan-bodied & Black-winged Tan & Black 253 253 80 79 159 Forward Males x Blue-bodied & Blue & Clear 25 24 49 Clear-winged Females Blue & Black 207 207 83 82 165 460 215 210 425 Tan & Clear 85g 46 131 Blue-bodied & Clear- Tan & Black 184 361 146 231 377 Reverse winged Males x Tan-bodied Blue & Clear 39 39 & Black-winged Females Blue & Black 120 120 667 361 351 316 A. By what mode (chromosome type & dominance) is the \'blue body\' mutation inherited? B. By what mode (chromosome type & dominance) is the \'black wing\' mutation inherited? C. Are the two traits linked? What specific piece(s) of offspring evidence led (leads) to that conclusion?

Solution

One mutation, blue body results in the entire body being bright blue, whereas the body color of wildtype flies is tan. A second mutation, black wings, shows very dark wings, whereas the wings of wildtype flies are clear. Lets also say that you were able to culture true-breeding populations of both mutations and then you tested the inheritance of each by performing a set of reciprocal crosses with true-breeding flies.

A. There are two basic modes of inheritance. One is autosomal inheritance which is carried by the autosomal chromosomes. Another is the inheritance by sex chromosomes, calles sex linked inheritance. There is an easy way to identify whether the inheritance is autosomal or sex lined. A simple receprocal cross; Here the parents are exchanged and resulting offspring is checked for mutation. For example the          

                                Tan bodied black winged male x Blue bodied clear winged female

                                Blue bodied clear winged female x Tan bodied black winged male

The result of reciprocal cross (see F1 of both) is different. This indicates that the inheritance is Sex linked. If the inheritance is autosomal, the results of reciprocal crosses would have been same.

In the reciprocal cross, all progeny is in tan and black. This means the inheritance is sex linked. In the reverse cross F1 generation, all progeny is Tan color, blue is lost altogether, which appeared in its F2 generation. A dominant allele is not lost in any generation. Hence the Blue color must be a recessive character.

B. Again by similar logic, the Black wing mutation is sex linked. And is dominant in nature.

c. To find out whether genes are linked, we need to find out how many parental and test progeny.

In the crosses: the parental types are not the most abundant types. If the linkage was not there then only 2 parental types should emerge in 50:50 ratio. But here the recombination types are also in abundance. So the traits are linked.