handling replicate and repeat measurement in ANOVA

Sorry for this relatively simple question which need a long explanation

In a experiment,
--> to illustrate: I am counting the number of step that mice need to walk trough a 10 cm long beam

I have 4 different groups (group A, group B, group C and group D)
-> A) non transgenic animals with B) or without treatment, C) transgenic animal with D) or without treatment

I have in each group a number of replicate (n) different
--> n(A) = 15 ; n(B) = 10 ; n(A) = 14 ; n(A) = 9

I have a number of measurement (m) different for each replicate (n)
--> we do 20 experiements and keep results only when mice do not stop during walking

We will consider an ideal case with normal distribution and equal variances


Can I perform an analysis of the variance (ANOVA) with a different amount of replicate in each group? Or does it influence so much the equality of variances that I can´t use data like that?

May I use ANOVA with a different amount of measurement in each replicate? And if not, how do you choose which replicates have to be "excluded"?

Thank you