How well do you understand genetics? Do you understand sex linked genes? I'm not sure what level to start and don't want to talk down to you. I'll try to be kind of basic but if you need clarification please feel free to ask.
Genes come in gene pairs. You never know which one of the genes at that gene pair a hen or rooster will pass on to their offspring. If both of those genes are the same it doesn't matter but many are not the same. They are passed down at random so it adds to confusion, especially when you are breeding crosses or hybrids. That's where the phrase "don't breed true" comes from, you never know which genes are getting passed down when they are different at that gene pair and crosses can have a lot of differences.
With chickens the hen is the one that determines the sex of the chick. Both parents contribute equally to genetics except for the sex linked genes. A hen gives a copy of all her genes to her boys but holds back some to her daughters. If the gene we are talking about is one of these sex linked genes the hen gives it to her sons but not her daughters. The rooster will give that gene to all his offspring, sons and daughters. If it is a sex linked gene, a pullet can only get it from her father.
If the hen has the dominant version and the rooster had two copies of the recessive version then a cockerel will get the hen's dominant version and show that trait. A pullet will only get her father's recessive version and show that trait. But the cockerel will also have a copy of the recessive gene to pass down randomly. The pullet will not.
The Rangers and Cornish X breeders keep different flocks to produce the parents of the actual Rangers and Cornish X. That topic is it's own long post so I'll skip a lot on that. With some strains of Rangers and CX the breeders use dwarfish on the maternal side. The chickens still have all the genetics to put on meat fast and all that, but the dwarf bodies means they don't have to spend as much on feed. There are probably some housing efficiencies too. Some strains of Rangers and CX use dwarfism, some don't. I don't know which do or don't.
What this means is that the mother of these Ranger strains has the dwarfism gene and gives it to her sons. The father gives the not-dwarfism gene to both his sons and daughters. His daughters will not have any dwarfism genes. His sons will have one recessive dwarfism gene from the mother and one dominant not-dwarfism gene from the father so he will not exhibit dwarfism. But he will randomly pass down each gene. Approximately half his offspring will get that dwarfism gene. So half his daughters will show dwarfism, half will not. Unless they get the dwarfism gene from their mothers his sons will not show it but half will have it to pass down.
What this means is that if you breed the girls from the Rangers with a rooster that does not have the dwarfism gene you will not have any dwarfism in your flock. If you breed a boy from the Rangers and you happen to get a strain that uses dwarfism then he can pass it to his offspring. I don't know which strains those are.
