Chapter 10, Problem 18A

Summary Introduction

To explain:

The chances of a family with five boys and no girl to have a sixth child as a girl

Introduction:

Reproductive cells which pass on genetic traits from the parent to child are produced by the process of meiosis. In order to maintain the same number of chromosomes in each generation, an organism produces gametes. The segregation of sex chromosomes and random combination of sperm and egg results in formation of males and females.

Answer to Problem 18A

No, there is no surety that the sixth offspring will be a girl. There is 50% chance for a child to be a boy or a girl.

Explanation of Solution

The chances of a child to be born as a male or a female is 50%. Gender of a child is not dependent on the previous birth. It is dependent on the father of the child. Gender of a child is determined by the sex chromosomes of the man. There are two types of sex chromosomes; X and Y. Individuals with two X chromosomes are female and those with an X and a Y are males. A man produces sperms that carry either X chromosome or Y chromosome. If the sperm carrying X chromosome fuses with egg of mother which carries X chromosome the resultant offspring will be a girl (XX). If the sperm carrying Y chromosome fuses with egg of mother which carries X chromosome the resultant offspring will be a boy (XY). So there are 50% chances for a child to be a boy or a girl. A man can produce both male and female child. This can be also checked by drawing a Punnett square as shown below.

	X	Y
X	XX	XY
X	XX	XY

The male is to female ratio is 1:1.