>create table test(gender varchar2(1))

>insert into test values('M');

>insert into test values('M');

>insert into test values('M');

>insert into test values('M');

>insert into test values('F');

>insert into test values('F');

>insert into test values('F');

select * from test

SQL> select * from test;

G
-
M
M
M
M
F
F
F

7 rows selected.

SQL> with trn as
  2    (select gender,
  3            row_number() over (partition by gender order by rownum) rn
  4     from test
  5    )
  6  select gender
  7  from trn
  8  order by rn, gender desc;

G
-
M
F
M
F
M
F
M

7 rows selected.

SQL>