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.

What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes? Explain your answer.

Accepted Answer

Welcome back, everyone. Here's our next question. Which types of chromosomes are usually involved in Robertsonian translocation choice. A Metacentric Choice B Acrocentric Choice C, telocentric choice D, both A and B and Choice E both B and C. So let's recall from our content videos, what a Robertsonian translocation is. And this is when you have the long arm of one chromosome that becomes attached to a non homologous chromosome with the consequent loss of the short arm and the centromere of the second chromosome. So you have this kind of formation of a new chromosome with the long arm of one being attached and you have the resultant chromosome with two long arms from two different chromosomes. You also lose a short arm of the first chromosome with that attachment. And as you can see in this description of long arm and short arm, we're generally looking for chromosomes that have a short arm and a long arm. So you're losing sort of a negligible amount of genetic information only losing this short arm. Well, that rules out choice. A Metacentric as metacentric chromosomes have arms of roughly equal length. So you aren't going to have that short arm, long arm disparity where you're joining two long arms and losing the little short bits. So choice A, we're gonna rule out or we're going to rule out and we're also going to rule out choice D, which is both A and B acrocentric chromosomes do have the centromere arranged so that you have two sort of long arms. We're imagining our X shaped chromosome with two chromatis and then a little short arm up on top. So they're ideal for this type of translocation and are often the types that are involved in a Robertsonian translocation. But choice C telocentric can also be involved in this. Uh because telocentric chromosomes have essentially no short arm, they just have the centromere and the two long arms. So they're also a candidate for this since they don't even have that little bit of information there and you can attach a long arm of a second chromosome onto that portion there. So since both B and C are correct answers, we're going to select as our answer. Choice. Choice E here, which is both B and C as the types of chromosomes usually involved in Robertsonian translocation. 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.

What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes? Explain your answer.

Key Concepts

Chromosomal Abnormalities

Mendelian Genetics

Probability in Genetics

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.What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes? Explain your answer.

Key Concepts

Chromosomal Abnormalities

Mendelian Genetics

Probability in Genetics

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.

What is the probability the next child of this couple will have a normal phenotype and have 46 chromosomes? Explain your answer.