Question

In humans, there is a 50% probability of the birth of a boy and 50 % probability
that a girl will be born. Justify the statement on the basis of the mechanism of sexdetermination in human beings

Answer 1

Justification of statement is as follows

• Sex determination depends upon the presence of sex chromosomes. There exists two types of sex chromosomes namely X and Y chromosome.

• Females carry XX sex chromosomes while males carry XY chromosome. X chromosome from father results in girl child while Y chromosome from father results in boy child.

• Hence, their exists 50% chance of fertilization of X carrying ovum(from mother), by sperm carrying X or Y chromosome(from father). Thus, the given statement is justified.

Answer 2

ANSWER :

In human,

• Male have 44+XY chromosomes

• Female have 44+XX chromosomes

During birth a child receive half of his chromosomes from father and other half from mother ( total remaining same , that is equal to of either parents ).

• The male produce sperms , which are either 22+X or 22+Y

• The female produce ovum which have 22+X only.

When zygote is formed by fertilization of sperm and ovum , there are two possibilities

1. The sperm having 22+X will fertilize the egg ( 22+X )
2. The sperm having 22+Y will fertilize the egg ( 22+X)

In 1st case , the zygote formed will have 44+XX chromosomes and hence will be female child.

In 2nd case , the zygote formed will have 44+XY chromosomes and hence will be male child.

As we can see there are only 2 possible outcome ( 1 boy and 1 girl ) , so probability of child being boy or being girl is equal, and which is equal to 50%.