It is not unusual to hear of sons or daughters following in their parents' footsteps and carrying on the family business. But what happens when the occupation is football? Willingness to learn and a desire to succeed are only useful when accompanied by natural talent, and the incidence of that being passed on in the genes is rare indeed.

Nonetheless, FIFA.com decided to investigate further and, after dusting down the record books and sifting through the archives, we found some fascinating cases that seem to be the exception to the rule. Fathers and sons, uncles and nephews, brothers and even twins, all of whom managed to keep their considerable talents in the family.

We found stories of families intricately linked to the FIFA World Cup. We asked Jean Djorkaeff about the advice he gave to his son Youri on starting out. We also look back at some of the classic Italian families and see what science has to say on the issue of footballing genetics.

In this our first series, we focus on some of the more unusual cases of footballing families in the modern game. 

Gudjohnsen
Iceland's Arnor Gudjohnsen saw his 17-year-old son Eidur follow in his footsteps - quite literally - when they both appeared for their country against Estonia in Talinn in 1996. Arnor, then 34, was already a veteran international who had won multiple league and cup honours and a top scorer's award in the Belgian league, while Eidur's career was just beginning. Then a cruel twist of fate saw the younger Gudjohnsen, now with English side Chelsea, miss the best part of two seasons with recurring knee injuries. By the time Eidur was again on international duty, his father had hung up his boots and the two never played in the same side again. "I think it's a real pity we couldn't have played together more, and I know Eidur feels the same," his father said recently.

European rights in the Sanchis family
One of Real Madrid's all-time greats, defender Manolo Sanchis, first stood on the famous Bernabeu turf as a five-year-old when he posed for a team photo with his father, a supremely gifted member of the legendary Madrid side of the 60s. A European Cup winner in 1966 when the club won their sixth continental crown, Manuel senior was known to finish all footballing arguments in the Sanchis household by telling his son that only when he had won the European title could he talk with any authority about the game. Perhaps this spurred young Manolo on, because on 20 May 1998, he was in the Madrid side that won the club's seventh European crown in Amsterdam, and was back two years later to win their eighth in Paris. Whether Manuel senior still holds sway in discussions on European football is not known.

The keeper is Kelly
The clash between English league sides Preston North End and Bury on January 1990 was unusual in that the team's respective goalkeepers were the Kelly brothers. The younger of the two, Alan, 21, played for Preston, while Gary, 23, kept goal for Bury. Furthermore, the players' father was the legendary Irish goalkeeper Alan Kelly, who lined up 47 times for his country and also made his name defending the colours of Preston North End. Of the two siblings, Alan Jnr. looks most likely to emulate his father's achievements after being selected as one of Ireland's goalkeepers for the 2002 FIFA World Cup Korea/Japan™.

Hugo Sanchez
Mexico's legendary striker and current coach of Pumas UNAM is just the latest in a long line of managers who have had to work with their own offspring. Hugo Sanchez junior is hoping to emulate his father, himself a former Pumas star, and is currently pushing hard for a first team spot. Though the young defender has a hard act to follow, he is a popular figure with supporters and warmly greeted whenever he takes to the field

Sibling rivalry
Gabriel Milito, a defender with Independiente, and his brother Diego, a striker with Racing, were on opposing sides in 2003 when their clubs met in the Avellaneda derby, one of the classics of Argentine football. Sixteen minutes into the game, Gaby pulled on the shirt of a Racing striker as he ran towards the area. The referee produced yellow and not red, despite a clamour for his expulsion by, among others, his brother Diego. The siblings then had what could best be described as a heated exchange before the free kick was finally taken.

There was more to follow. Seven minutes later, Diego was on the ball in midfield when he was dispossessed unceremoniously by Gaby. Such was the ferocity of the tackle that the striker's right boot came clean off. Understandably aggrieved, the Racing man ran boot in hand to remonstrate with the referee only to earn a yellow card for his troubles. The father of the warring pair, who was at the game, said afterwards: "I was surprised to see Diego calling for Gaby to be sent off, and to see them arguing. At least with this row, there'll have been no derogatory remarks about the other guy's mother".

Johan and Jordi Cruyff
The star of the great Dutch side of Germany 1974, Johan Cruyff followed a hugely successful playing career with a move into management that eventually saw him in at the helm of the Barcelona "Dream Team" of the early 90s. However by the 94/95 season, only remnants of the team remained and with no title to show, the team's entire season hinged on qualifying for the UEFA Cup in their final game. This they duly did, with the winning goal coming from none other than the boss's son Jordi. The priceless strike did wonders for the youngster's confidence and helped silence many of the dissenting voices at the club.

Twin centuries
Twins Hossam and Ibrahim Hassan are two brothers very much in sync. The Egyptian internationals are the most capped players in Africa and members of the exclusive century club, having won 160 and 125 caps respectively. Their playing careers have followed remarkably similar paths, taking them from al-Ahly in Egypt to Paok Salonica in Greece to Neuchatel Xamax in Switzerland before they were reunited again at al-Ahly's arch-rivals Zamalek, where they won the title in their first season. Hossam is the most successful Egyptian footballer of all time with 38 titles, while his brother occupies second spot with 31. "Many years ago, we dreamed we'd one day play together and terrorise opponents - Ibrahim at the back and me up front. We worked for it from when we were little boys playing in the streets and in the end we made it", said Hossam.

The Generation Game
Yehia Emam kept goal for Egypt at the London Olympics in 1948 and won 12 Egyptian League titles and four Egyptian Cup titles with Zamalek. Yehia's passion for the sport must have rubbed off on his son Hamada because he followed his father into the game. Though his job was to score goals and not stop them, he was no less successful, winning two league titles and three cups also with Zamalek. But there was more to come. Grandson Hazem became the third generation of Enam players to win honours with the famous club, becoming a local and national hero with ten titles, 81 caps and 15 international goals. Among his many distinctions was his role in the team's 2002 victory in the African Champions League.

The Andrianopoulos dynasty
The Andrianopoulos brothers hail from one of Greece's foremost footballing families. Their father, Andreas, a wealthy businessman and member of Piraeus high society, co-founded Olympiakos in 1925. His athletically gifted sons would later spearhead the side during the club's golden era in the 30s. Initially there were four brothers in the side - Giannis, Dinos, Giorgos and Vassilis - all strikers, but they were later joined by a fifth, Leonidas. There was a sixth brother, Stelios, who played for some time but was not of the same calibre as his other siblings. Dinos, Vassilis and Giorgos were part of the first Olympiakos side to win the Greek League title (1930-31) and members of the Greek national team when they played their first official international on 7 April 1929. 

Brothers on the double
When Northern Ireland and Wales met at Windsor Park on 20 April 1955, there was one very unusual feature in the starting line-up. The Welsh coach had opted to play not one, but two sets of brothers against the Irish: John and Mel Charles and Len and Ivor Allchurch. Wales won 3-2 win on the night

Relative values
Malian striker Salif Keita was one of the biggest names in African football in the late 60s and early 70s. He also earned iconic status at French side Saint- Etienne where he won three league titles and scored 120 goals in 149 appearances - including 42 in one season to finish as Europe's second highest goalscorer. When Salif later established Africa's first football academy, one of its most promising students was none other than his nephew, Seydou Keita. "He was a hard taskmaster. He knew I had talent and aptitude but felt I was too laidback for my own good," recalls Seydou.

Under his uncle's watchful eye, the young Keita matured into a fully-fledged professional and signed for Marseille. In 1999, he won the Golden Ball at that year's FIFA World Youth Championship in Nigeria, where Mali surprised everyone by reaching the semi-finals. Today, he is a important member of the country's senior side and a valued player at his club Lens. 

Keeping up with the Jones'
The Jones brothers, Williams, Ivor, Emlyn, Bert and Bryn, earned fame in the 30s and 40s when they played in the Welsh league. Three of the five would later see their offspring follow them into the professional game. The most famous of the second generation of Jones was Ivor's son Cliff, who represented Wales at the 1958 FIFA World Cup in Sweden and also played in the legendary Tottenham Hotspur side that won the English league and cup double in 1961.

Double Dutch
Although physically very similar, the Dutch twins Ronald and Frank de Boer were easily distinguished by their individual playing styles on the pitch. Having earned a reputation at Ajax, the pair headed off to play for FC Barcelona in 1999. The previous year they were part of the Netherlands side that reached the last four at France 98, when their semi-final against Brazil finished 1-1 and went to penalties.  As fate would have it, it was Taffarel's save from Ronald de Boer that consigned the Dutch to defeat and sent the Auriverde through to the final. As the rest of the players consoled each other and tried to comfort Ronald, Frank approached his brother and berated him unmercifully for the miss. It was the sort of thing that only brothers, or perhaps just twins, could get away with. 

My son, number 9
Brian Clough scored a phenomenal 251 goals in 274 games for Middlesbrough and Sunderland between 1955 and 1962 before his career was tragically cut short by a cruciate ligament injury. His passion and knowledge of the game saw him go into coaching and eventually become manager at Nottingham Forest, where he won back-to-back European Cups in 1979 and 1980. When his son Nigel, a talented centre-forward, broke into the first Forest team in the mid eighties, Clough senior insisted on referring to him obliquely as "our number 9" in the presence of the other players. Nigel would later follow his father's footsteps into management.