Sex Determination – Long Answer Questions

Medium Level (Application & Explanation)

Q1. Explain the role of sex chromosomes in determining the sex of a child in humans.

Answer:

Sex in humans is determined by special chromosomes called sex chromosomes.
Each parent provides one sex chromosome to the child.
Females have two X chromosomes (XX) and can only pass an X chromosome through their egg.
Males have one X and one Y chromosome (XY), so the sperm can carry either X or Y.
If the child receives X from both parents, the result is XX—a female.
If the child receives an X from the mother and Y from the father, the result is XY—a male.

Q2. Why is it said that the father determines the sex of the child in humans? Support your answer.

Answer:

The mother always contributes an X chromosome since females have XX sex chromosomes.
The father's sperm may carry either an X or a Y chromosome (as males are XY).
If the sperm with an X fertilizes the egg, the offspring will be a girl (XX).
If the sperm with a Y fertilizes the egg, a boy (XY) will be born.
Therefore, the father’s sperm is responsible for determining if the baby is male or female.
This proves the father’s genetic contribution determines the child’s sex.

Q3. How is the process of sex determination in birds different from humans?

Answer:

In birds, the sex chromosomes are named Z and W instead of X and Y.
Male birds have two Z chromosomes (ZZ) and females have one Z and one W (ZW).
The egg from the mother may carry a Z or a W chromosome.
The sperm from the father always carries a Z chromosome.
If the egg is Z, a ZZ (male) chick is born; if W, a ZW (female) chick is born.
So, in birds, the mother (egg) determines the sex of the offspring.

Q4. Discuss the sex determination mechanism in honey bees and how it results in female and male bees.

Answer:

In honey bees, sex determination depends on whether the egg is fertilized.
Fertilized eggs become female bees (workers or queen) and have two sets of chromosomes (diploid).
Unfertilized eggs become males (drones) and have only one chromosome set (haploid).
This unique system is called haplodiploidy.
Unlike humans, there are no special sex chromosomes involved.
Fertilization decides the bee’s sex, not the chromosome combinations.

Q5. Explain with a diagram how chromosomal combinations result in boys and girls in humans.

Answer:

In humans, females are XX and males are XY.
The mother’s eggs all contain X chromosomes, but the father’s sperm may have either X or Y.
At fertilization:
- X (egg) + X (sperm) = XX (girl)
- X (egg) + Y (sperm) = XY (boy)

A simple diagram:


Mother (XX):           X           X
                     ↘           ↙
Father (XY):       X     or    Y
                → X+X       X+Y
                → XX (Girl) XY (Boy)

This shows that the combination of sex chromosomes decides the child’s sex.

High Complexity (Analysis & Scenario-Based)

Q6. Imagine a population where there is a high number of X chromosomes but a shortage of Y chromosomes among males. Predict the possible impact on the sex ratio of newborn babies over time.

Answer:

In humans, children become male if sperm carries a Y chromosome and female if sperm carries an X chromosome.
If Y chromosomes are rare among males, fewer sperm can produce male (XY) children.
This would lead to more girls (XX) being born than boys.
Over generations, the population could develop a higher female-to-male sex ratio.
Fewer males being born could affect societal balance and population growth.
This scenario shows how chromosome supplies in sperm can impact population structure.

Q7. A family keeps blaming the mother for not having a male child. Use scientific logic to refute this belief.

Answer:

The sex of a child is determined by which sex chromosome comes from the father’s sperm.
The mother only produces eggs with X chromosomes (she is XX).
The father’s sperm can contain either X or Y chromosomes (he is XY), and it’s the sperm type that decides the child’s sex.
If a Y-carrying sperm fertilizes the egg, the baby will be a boy (XY); if an X, a girl (XX).
Thus, the mother cannot influence the child’s sex—the key factor is the sperm from the father.
Science proves it is unfair and incorrect to blame mothers for child’s sex.

Q8. Environmental factors sometimes affect sex determination in some species. Explain how this differs from the chromosomal method seen in humans, giving an example.

Answer:

In humans, sex is set at fertilization by the combination of sex chromosomes (XX or XY).
In some reptiles (like turtles or crocodiles), sex is not fixed by chromosomes but by the temperature at which eggs develop.
For instance, in many turtles, cooler incubation produces males, while warmer conditions produce females.
This process is called environmental sex determination.
The difference lies in humans using genetic (chromosomal) cues, while reptiles use external (environmental) signals.
Therefore, environment—not genes—chooses the sex in these species.

Q9. If a pair has two children, both girls, what are the chances that their third child will be a boy? Explain using the principles of sex determination.

Answer:

Each child’s sex is decided independently by the sperm that fertilizes the egg.
The mother always provides an X chromosome, while the father can supply either X or Y.
The chance is always 50% for boy (XY) and 50% for girl (XX), regardless of previous children.
Having two daughters earlier does not change the chances for the third child.
This is because previous pregnancies do not influence which sperm wins the race this time.
So, the chance for the third child to be a boy is still 50%.

Q10. Discuss the social importance of people understanding the real mechanism behind sex determination in humans.

Answer:

Knowing the scientific facts removes blame from mothers for a child’s sex, promoting gender equality.
It can help reduce female foeticide and discrimination against girls by correcting myths.
Society will know only men carry the chromosome that can create a boy (Y), so blaming mothers is wrong.
This understanding supports the dignity and rights of women and helps stop unequal treatment.
With correct knowledge, people can focus on the child’s growth, health, and happiness, not just their gender.
Thus, science education is important for healthier, more equal societies.