Statement 4 is incorrect. in birds (like domesticated fowls), the mechanism of sex determination involves female heterogamety (ZW) and male homogamety (ZZ). Females produce two different types of gametes (eggs carrying Z or W), while males produce only one type of sperm (carrying Z). Therefore, the sex of the progeny depends on the type of egg that is fertilised, not the sperm .

Correctness of other options:

1. Human males are XY, and the Y chromosome is morphologically smaller than the X (implied by standard karyotypes shown in Figure 4.17b, though text focuses on composition).
2. Male fruit flies (Drosophila) are heterogametic (produce two types of sperms, X and Y) .
3. Male grasshoppers have XO sex determination; 50% of sperms have the X chromosome and 50% have no sex chromosome .