Query posts using dropdown menu of custom fields

I have created this category archive which contains a table of 100 posts. The table contains 3 custom fields (Gender,Continent,Sector) and there is also a fourth (‘Overall’ with the only value ‘All’) which is not inside the table and their values for each post are inside the table cells of every entry/post.
I have placed above the table four select tags (the four drop down menus) which I would like to filter the posts depending on which option of a certain select tag is chosen. To be more specific when a user choses for example select tag ‘Continent’ and option ‘Europe’ I would to query all posts with custom field value ‘Europe’. Is it possible to do that by using an if statement and how exactly would I syntax that? The select tags are the following:

For custom field Overall

<select>
<option value="all">All</option>
</select> 

For custom field Gender

<select>
<option value="gender">Select Gender</option>
<option value="male" >Male</option>
<option value="female">Female</option>
</select>

For custom field Continent

<select>                    
<option value="continent">Select Continent</option>
<option value="europe">Europe</option>
<option value="america">America</option>
<option value="africa">Africa</option>
<option value="asia">Asia</option></select>

For custom field Sector

<select> 
<option value="sector">Select Sector</option>
<option value="retail">FMCG/Retail</option>
<option value="various">Various</option>
<option value="finance">Finance</option>
<option value="se">SE</option>
<option value="energy">Energy</option>
<option value="education">Education</option>
<option value="fb">F&B</option>
<option value="environment">Environment </option>
<option value="telco">Tech/telco </option>
<option value="fashion">Fashion </option>
<option value="media">Media </option>
<option value="construction">Construction </option>
<option value="health">Health </option>
<option value="tech">Tech </option>
<option value="industry">Industry </option>
</select>