Null hypothesis of Chi-square test for independence
It might help if you first ask yourself what the independence test is for in plain English, you are testing to see if one categorical variable has 
an influence on another. In other words, if a person (or whatever)with attribute X (for example, is bald) are they significantly more/less likely to have attribute Y (like being allergic to penicillin) than someone who does not have attribute X. 

So in your example the alternative hypothesis would be (in words): the ratio of males with attached ear lobes compared to males without is equal to the ratio of females with attached ear lobes compared to those without.