How do the Roloffs from "Little People, Big World" have three normal sized children?

Question

This has been plaguing me for a while. In the show, "Little People, Big World" the Roloff Family is comprised of two dwarf parents, one dwarf son, and three normal size children. Now from what I've learned in genetics class (and my little internet research) dwarfism comes from a recessive gene. That means that for someone to be a dwarf phenotypically, they have to possess two dwarf genes and no "normal size" genes, because even one "normal size" gene will result in the child being of normal size. But the Roloffs, who are both dwarfs, have not one, but THREE normal sized kids.

How is this genetically possible?

UPDATE: Before I posted this question, I checked online and there was a website that told me that the dwarfism gene is recessive. After further searching (and special thanks to those who responded, I found out that the dwarfism gene is, in fact, dominant, which makes more sense.
Thanks to those who responded. Thumbs up for all of you!

Answer 1

The are both dominant for dwarfism. If they have normal sized kids then the must also have recessives as well (i.e. heterozygous - Dd). So with each birth (using a Punnet square), they have a 25% chance of having a homozygous dominant child (DD), a 25% chance of having a homozygous recessive child(dd - this child will NOT be a dwarf), and a 50% chance of having a heterozygous dominant child (Dd). The could have had 10 normal kids if those were the genes that got passed down. So, apparently their 3 normal kids all got a recessive from each parent so they are dd. The odds were low but it so random it can happen. Their twins are fraternal since one is DD or Dd and the other is dd. So two eggs were fertilized by 2 different sperm carrying different genes. Its all pretty random and its more far complicated than I've laid out but this gives a basic idea.

Answer 2

Amy has achondroplasia, which is a dominant genetic disorder. People with achondroplasia have one mutated gene and one normal gene (or a differently mutated gene, a fetus with the disorder on both genes would die before birth). Matt has diastrophic dysplasia which is a recessive genetic disorder. People with diastrophic dysplasia have TWO mutated genes.

This means that their one dwarf child, who has achondroplasia, has one mutated gene for achondroplasia and one mutated gene for diastrophic displasia. The diastrophic displasia gene is not manifested because you need TWO in order to have the disease. Matt and Amy's other three children have one normal gene and one gene for diastrophic displasia. Again, they are normal height because diastrophic displasia is a recessive disorder. It's also a very rare form of dwarfism, so even if they passed along the mutated gene when they have children, unless their spouse also has a gene for diastrophic displasia all of their children have the same odds of being normal height as the general population.

For each individual pregnancy, Amy and Matt had a 50/50 chance of having a child with acondroplasia, and a 0 percent chance of having a child with diastrophic displasia. In one of the cases Amy passed along her achondroplasia gene, and in the other three she passed along her normal gene, and that's why three of the children are normal height and only one is a dwarf.

Answer 3

Actually the most common type of dwarfism is carried by a Little person as one dwarf gene one regular gene, so they can pass on either a regular or dwarf gene so they can easily have a "normal size" child. the chances are 25% which means that the "normal gene is recessive not the dwarf gene.
check out the FAQ's on this site:
http://www.lpaonline/mc/page.do?sitePageId=37298&orgId=lpa

Answer 4

The parental genes are dominant recessive. This means that the recessive gene is dominant. They only need one of the "little people" genes to express the trait. If you make a punitz square and figure it out. There is a possibility to have a normal child. Both of the parents must have one normal gene, but the "little people" gene overrides it. If a child gets the one normal gene from each parent, it forms a normal child.

Answer 5

Big People Little World

Answer 6

And the genetic mutations will always continue as long as they keep having kids and then those kids pass down the mutation and so on and so on.

Answer 7

You might need to reconsider since i am pretty sure Amy's their mom) has normal height parents.

Answer 8

Thank you for all the answers!

Answer 9

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