Chapter 8.3, Problem 32AQP

a.

Summary Introduction

To explain:

Whether the statementBill has $47$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

In the given case, it is nowhere mentioned that Bill is suffering from Down syndrome. $47$ chromosomes represent trisomy which is not there in Bill. So, the statementBill has $47$ chromosomes statement is incorrect.

b.

Summary Introduction

To explain:

Whether the statement that Betty has $47$ chromosome is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

In the given case, no information has been provided for Betty. It is nowhere mentioned that she is having a trisomy that is total number of chromosomes are $47$. So the number of chromosomes in cells of Betty are $46$. So the statement thatBetty has $47$ chromosome is incorrect.

c.

Summary Introduction

To explain:

Whether the statement Bill and Betty’s children each have $47$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

Both the children of Bill and Betty have Down syndrome. However, since Bill is normal, he must be the carrier for Robertsonian translocation. He will transmit translocated copy of chromosome $21$. So, both the children of Bill and Betty must have translocated copy. The number of chromosomes in children would be $46$. So, the statement that Bill and Betty’s children each have $47$ chromosomes is incorrect.

d.

Summary Introduction

To explain:

Whether the statement Bill’s sister has $45$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

Since the children of both Bill and his sister have Down syndrome, this reflects that both Bill and his sister must be carrier for Robertsonian translocation. One of the chromosomes produced by Robertsonian translocation has long arms of both chromosome $14$ and chromosome $21$ and the other chromosome have short arms of both chromosome $14$ and chromosome $21$. The chromosome having short arms is lost. Hence, both Bill and his sisters will have $45$ chromosomes. So, the statement that Bill’s sister has $45$ chromosomes is correct.

d.

Summary Introduction

To explain:

Whether the statement Bill’s sister has $45$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

Since the children of both Bill and his sister have Down syndrome, this reflects that both Bill and his sister must be carrier for Robertsonian translocation. One of the chromosomes produced by Robertsonian translocation has long arms of both chromosome $14$ and chromosome $21$ and the other chromosome have short arms of both chromosome $14$ and chromosome $21$. The chromosome having short arms is lost. Hence, both Bill and his sisters will have $45$ chromosomes. So, the statement that Bill’s sister has $45$ chromosomes is correct.

e.

Summary Introduction

To explain:

Whether the statement that Bill has $46$ chromosome is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

The children of Bill have Down syndrome. The Down syndrome is passed from Bill as no history of Betty is given. Bill is the carrier of translocation of chromosome $21$. So, he must be having $45$ chromosomes. So, the statement that Bill has $45$ chromosomes is correct.

f.

Summary Introduction

To explain:

Whether the statement Betty has $45$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

The children of Bill have Down syndrome. In the family of Bill, familial Down syndrome is getting transmitted. So Bill is the carrier of Robertsonian translocation, and Betty has normal number of chromosomes. So, the statement that Betty has $45$ chromosomes is incorrect.

g.

Summary Introduction

To explain:

Whether the statement Bill’s brother has $45$ chromosomes is correct or incorrect.

Introduction:

Trisomy is the addition of a single chromosome in the whole set of chromosome. Addition of single chromosome refers to the gain of one extra homologous copy of individual chromosome. Trisomy is represented as $\text{2n}+\text{1}$. Down syndrome is the trisomy of chromosome $21$.

Explanation of Solution

Bill’s brother has Down syndrome and he is not the carrier for Robertsonian translocation. He must be having $47$ chromosomes. So, the statement that Bill’s brother has $45$ chromosomes is incorrect.

Conclusion

Down syndrome is the trisomy of chromosome $21$. It is of two types, namely- primary Down syndrome and Familial Down syndrome. Familial Down syndrome is produced by Robertsonian translocation and primary Down syndrome is caused by nondisjunction of chromosome $21$. The carrier of Familial Down syndrome has $45$ chromosomes whereas person with Down syndrome have $47$ chromosomes.