C
CraftExam
medium difficulty6 min

Sex Determination

Sex determination is the process by which the sex of an offspring is decided at fertilisation.

In one line: Mother gives X, father gives X or Y.

Practice This Concept

Understand it

  • In humans, the mother has XX chromosomes and the father has XY chromosomes.
  • The mother always contributes an X chromosome through the egg, while the father can contribute either X or Y through the sperm.
  • If the sperm carries X, the child is XX and develops as female.
  • If the sperm carries Y, the child is XY and develops as male.

Example

A human baby receives one sex chromosome from each parent. An X-bearing sperm produces a girl child, and a Y-bearing sperm produces a boy child.

Rule to remember

Human sex chromosomes: female = XX, male = XY; egg always carries X, sperm carries X or Y.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

  1. 1If an X-bearing sperm fertilises the X-bearing egg, the zygote becomes XX and the child is female.
  2. 2If a Y-bearing sperm fertilises the same egg, the zygote becomes XY and the child is male.

Method you can reuse

  1. 1Recall the mother's sex chromosomes.
  2. 2Recall the father's sex chromosomes.
  3. 3Note that the egg always has X.
  4. 4Check whether the sperm has X or Y.
  5. 5Write XX or XY and state the sex.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

In humans, which parent can contribute either X or Y chromosome to decide the baby's sex?

Think first, then show answer
The father contributes either an X or a Y chromosome through the sperm, so the father's sperm decides the baby's sex at fertilisation.

Common wrong answer

A common wrong answer is to say the mother decides the sex because the child develops in her body. That is incorrect in human sex determination.

Don't mix this up

Students often think the mother decides the sex of the baby. That is wrong because the father's sperm can carry either X or Y.

Exam tip

Always write XX for female and XY for male in humans. Mention that the father's sperm determines the final combination.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Explain why the father determines the sex of the child in humans, or write the chromosome combinations for male and female.
  1. 1

    Enough for 1 mark

    Sex determination is the process by which the sex of an offspring is decided at fertilisation.

  2. 2

    Add for 2 marks

    Example: A human baby receives one sex chromosome from each parent. An X-bearing sperm produces a girl child, and a Y-bearing sperm produces a boy child.

  3. 3

    Add for 3 marks

    In humans, the mother has XX chromosomes and the father has XY chromosomes.

MCQ Quiz

Practice this concept with focused MCQs

Open the concept quiz intro first, review the test details, and then start a focused MCQ set from this concept only. Instant score and answer review are live now.

10 MCQs5 MinutesInstant Results
Practice This Concept

Help improve this page

Found something confusing, incorrect, or missing?

Practice This Concept