Crosses between two tailless mice produces tailless and wild-type offspring in a 2: 1 ratio. tailless mice crossed with wild-type mice produce a 1: 1 ratio of tailless to wild-type progeny. what is the best explanation?

In first generation one allele pair with an offspring  is lethal, hence the phenotypic ration is 2:1

Explanation:

Let the allele representing the  tailless trait with in mice be "t"

the allele representing the wild-type offspring  trait with in mice be "t+"

Generation I

Genotype of tailless mice is "tt+"

Cross between two tailless mice will produce following offspring

tt+ * tt+

tt, tt+, tt+, t+t+

Out of four offspring, the one with genotype "tt" is lethal, thus ration of tailless and wild-type offspring is

2:1

Generation I

Genotype of tailless mice is "tt+"

Genotype of wild-type offspring  is "t+t+"

Tailless mice crossed with wild-type mice produce-

tt+ * t+t+

tt+, tt+, t+t+,  t+t+

Ratio of tailless to wild-type progeny is

2:2

1:1