( CNN ) -- Whenever a new baby is on the way , the family ca n't help but speculate on what the little one might look like . Will he or she have straight hair like Dad or curly hair like Mom ? Be tall like Aunt Susan or short and stubby like Uncle Leroy ? When the new arrival is the future king or queen of England , more than just the family wants to know . Catherine , Duchess of Cambridge , is reportedly due to give birth July 13 , and the world will watch as the baby grows up . Will he or she turn out to have blue eyes like Prince William or green ones like Catherine ? Be light-haired like Dad or dark-haired like Mom ? Will Prince Charles ' ears be passed on to a future generation ? Online bets are already being placed on the child 's hair color . Whatever happens , this baby might stand out genetically among royals because his mother is the first commoner to marry into the royal family since the 17th century . Marriage within a relatively small gene pool , like the royals , means a bad gene has a pretty good chance of rearing its ugly head . The blood clotting disorder hemophilia , for example , has run in the British royal family . `` It 's very good that they 're bringing in new genes , '' said Dr. Anand Saggar , a consultant in the South West Thames Regional Genetics Department at St. George 's Hospital Medical School in London . `` It freshens up the gene pool . '' Royal baby slightly more likely to be female , scientist says . Catherine 's commoner genes might lead to a somewhat darker-skinned baby , Saggar said . The royals , he explained , are pretty pale . Catherine 's skin has a considerably more olive tone , and the baby will likely be somewhere between the two -- but more like Catherine because her genes are dominant over lighter ones . `` The odds are the child will have darker skin color than the royals might be used to , '' Saggar said . The same is true for eye color . The chances that the baby will have true blue eyes like William 's are relatively unlikely . Most likely , Saggar said , the baby 's eyes will be a shade closer to Catherine 's . With hair color , there are basically four options : light like Dad , dark like Mom , a shade in between the two or red like the baby 's Uncle Harry . Saggar said it 's possible to calculate the odds of a redhead . Based on the fact that William 's brother , Prince Harry , is a ginger , there 's a 66 % chance that William carries a gene for red hair , he said . Less is known about Catherine 's heritage , but assuming it 's similar to the genes of other British people , he calculates there 's a 6 % chance the baby will have red hair . Apparently Britons are more confident the baby will have red hair . At William Hill online betting , there are 4-1 odds the baby will be a ginger . `` If you 're going to put some money on it , you might want to think about it , '' Saggar said . While hair color might be debatable , one physical trait seems pretty clear : William and Catherine 's child will likely be quite tall . William is reportedly around 6 foot 3 inches tall , and his wife about 5 feet 10 inches . A son would likely be between 5 feet 11 inches and 6 feet 7 inches , and a daughter between 5 feet 6 inches and 6 feet 2 inches , according to Barry Starr , director of outreach at the department of genetics at Stanford University . Of course , it 's impossible to use genetics to predict completely what any baby will look like , royal or not . `` That 's the fun of having babies , '' Saggar said . `` You do n't know what you 're going to get . '' Video : Royal note to reveal baby 's gender . CNN 's John Bonifield and William Hudson contributed to this report .
The royal baby might have blue eyes like William or green ones like Catherine . It 's likely the baby will have darker skin than most royals , an expert says . Royal offspring may also have red hair like uncle -- Prince Harry .