Radio Button in Visualforce Page

<apex:page >
    <apex:form >
        <apex:pageBlock >
            <apex:pageBlockSection >
                <apex:pageBlockSectionItem >Gender
                    <apex:selectRadio >
                        <apex:selectOption itemLabel="Male" itemValue="m"/>
                        <apex:selectOption itemLabel="Female" itemValue="f"/>           
                    </apex:selectRadio>     
                </apex:pageBlockSectionItem>
            </apex:pageBlockSection>
        </apex:pageBlock>
    </apex:form>
</apex:page>