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Reaching the Age of Adolescence - Sex Determination and Reproductive Health

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The nucleus of every cell contains thread-like structures called chromosomes. Humans have 2323 pairs of chromosomes (4646 in total) in each cell.

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Out of these, two chromosomes are called sex chromosomes, designated as XX and YY. A female has two XX chromosomes (XXXX), while a male has one XX and one YY chromosome (XYXY).

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All unfertilized eggs always contain one XX chromosome. However, sperms are of two kinds: one kind has an XX chromosome, and the other has a YY chromosome.

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Sex Determination: If a sperm contributing an XX chromosome fertilizes the egg, the zygote will have XXXX and develop into a female child. If the sperm contributing a YY chromosome fertilizes the egg, the zygote will have XYXY and develop into a male child.

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Reproductive Health: Adolescents require a balanced diet including proteins, carbohydrates, fats, and vitamins. Iron (FeFe) is crucial for blood formation; hence, iron-rich foods like leafy vegetables and jaggery are essential.

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Personal Hygiene: Increased activity of sweat glands can cause body odor. Bacterial infections can occur if cleanliness is not maintained, especially during menstruation for girls.

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Say No to Drugs: Adolescence is a period of confusion and insecurity. Drugs are addictive and can ruin health and happiness. HIV can be transmitted through shared needles or from an infected mother to an infant through milk.

📐Formulae

Female Genotype=XX\text{Female Genotype} = XX

Male Genotype=XY\text{Male Genotype} = XY

Zygote (Female)=Xegg+Xsperm→XX\text{Zygote (Female)} = X_{\text{egg}} + X_{\text{sperm}} \rightarrow XX

Zygote (Male)=Xegg+Ysperm→XY\text{Zygote (Male)} = X_{\text{egg}} + Y_{\text{sperm}} \rightarrow XY

Calculation for full height (cm)=Present height (cm)% of full height at this age×100\text{Calculation for full height (cm)} = \frac{\text{Present height (cm)}}{\% \text{ of full height at this age}} \times 100

💡Examples

Problem 1:

Determine the probability of a couple having a girl child based on the chromosomal theory of sex determination.

Solution:

The probability is 50%50\% or 1:11:1.

Explanation:

Since the mother always provides an XX chromosome and the father provides either an XX or a YY chromosome with equal frequency (12\frac{1}{2}), there are two possible outcomes: XXXX (female) or XYXY (male). Thus, the ratio is 1:11:1.

Problem 2:

A 99-year-old boy is 120 cm120\text{ cm} tall. At the end of the growth period, he is likely to be what height? (Assume 75%75\% of full height is reached at age 99 for boys).

Solution:

Full height=12075×100=160 cm\text{Full height} = \frac{120}{75} \times 100 = 160\text{ cm}

Explanation:

Using the formula Present height% of full height×100\frac{\text{Present height}}{\% \text{ of full height}} \times 100, we substitute the given values to find the predicted adult height.

Problem 3:

Why is it traditionally and scientifically incorrect to blame the mother for the sex of the child?

Solution:

Because the mother's gamete is always XX.

Explanation:

The mother only possesses XXXX chromosomes and can only contribute an XX to the offspring. The sex of the child is determined by whether the father's sperm carries an XX or a YY chromosome. Therefore, the father's genetic contribution determines the sex.