A boy with Down syndrome (trisomy 21) has 46 chromosomes...

Question

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

How many chromosomes do you expect to see in karyotypes of the parents?

Accepted Answer

Hi, everyone. Welcome back. Here's our next problem. It says, determine which of the following statements about Robertsonian translocation is incorrect. So let's look through our answer choices and evaluate them. Remembering that we're looking for the incorrect statement. Choice. A says it involves the fusion of two non homologous chromosomes. Well, this is true that translocation does involve one nonhomologous chromosome fusing with another, a piece of one fusing onto the second. So that's not our answer choice since it is a correct statement. Choice B says it is also called chromosome fusion. Well, this is also true. That's another name since it fuses together two chromosomes. So not our answer. Cho C says it is accompanied by loss of one of the centromere and by the loss of a chromosome short P arm. Well, this is also a correct statement when the piece of one chromosome gets fused on to the second, it loses the centromere of the second chromosome and its short arm. Since that's true, then that's also not our answer. So finally, we're on choice D which says the chromosomes involved in it are usually metacentric or submetacentric chromosomes. Well, this is not correct the chromosomes involved in a Robertsonian translocation are usually acrocentric or telocentric. And that's because those types of chromosomes have either these very short arms in the case of acrocentric where you have a little tiny short arm or just no uh short arm at all, just like that with the centromere and then just one arm versus metacentric or submetacentric, which is more metacentric. Your centromere is right in the middle of two equal length arms and submetacentric where they're not exactly equal, but you still have a pretty substantial shorter arm. So again, you're most much more likely to have a Robertson Robertsonian translocation with the chromosomes that either don't have much of a short arm or don't have one at all. So choice D is our answer here. Again, which of the following statements about Robertsonian trans location is incorrect. Choice D the chromosomes involved in it are usually metacentric or submetacentric chromosomes. See you in the next video.

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

How many chromosomes do you expect to see in karyotypes of the parents?

Key Concepts

Karyotype

Aneuploidy

Inheritance Patterns

Watch next

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.How many chromosomes do you expect to see in karyotypes of the parents?

Key Concepts

Karyotype

Aneuploidy

Inheritance Patterns

Watch next

A boy with Down syndrome (trisomy 21) has 46 chromosomes. His parents and his two older sisters have a normal phenotype, but each has 45 chromosomes.

How many chromosomes do you expect to see in karyotypes of the parents?