Question

11) In the salamander species Ambystoma mercadoi, individuals may be spotted or unspotted. You cross a male and a female from different localities/populations, each of which is pure-breeding for the unspotted phenotype. The Fı progeny are all unspotted. You then cross two Fi's and obtain the following results for the F2 generation: 70 unspotted males 72 unspotted females 17 spotted males 16 spotted females A) Draw out the crosses described above, showing the genotypes of the parents, F, and F2 generations (10 pts.).

Answer 1

Pure-breeding or true-breeding is a process of mating in which the parents would produce offspring that would carry the same phenotype. However, their combinations of alleles differ. This means that the parents are homozygous for a particular trait and all of the offspring will be heterozygous for that trait.

In the given question, the salamander species Ambystoma mercadoi is mated to produce F1 offspring.

In the salamander species, the allele for the unspotted phenotype is dominant (S) and the allele for the spotted phenotype is recessive (s).

The genotype of parents are SS (unspotted) and ss (spotted), and their gametes are S and s.

The cross for pure breeding between an unspotted salamander and a spotted salamander is shown in the following Punnet square.

♂/ ♀	s	s
S	Ss Unspotted	Ss Unspotted
S	Ss Unspotted	Ss Unspotted

From the above Punnet square, it can be predicted that all offspring will be Unspotted.

Then, the F1 progeny is crossed to produce F2 progeny.

The cross between two F1 progeny is as follows:

♂/ ♀	S	s
S	SS Unspotted	Ss Unspotted
s	Ss Unspotted	ss spotted

By observing the Punnet square, SS and Ss include 142 (70+72) unspotted males and females and ss include 33 (17+16) spotted males and females.