Problem 8 - Biology: The Unity and Diversity of Life

Question

A female child inherits one \(X\) chromosome from her mother and one from her father. What sex chromosome does a male child inherit from each of his parents?

Step-by-Step Solution

Answer

A male child inherits an X chromosome from his mother and a Y chromosome from his father.

Step 1: Understanding Sex Chromosomes

Both males and females have two sex chromosomes. Females have two X chromosomes (XX), whereas males have one X and one Y chromosome (XY). This difference in chromosomes determines the sex of the child.

Step 2: Male Child Inheritance from Mother

A male child must inherit the X chromosome from his mother because the mother has two X chromosomes. This X chromosome allows the male child to have the pair of chromosomes necessary to determine gender.

Step 3: Male Child Inheritance from Father

A male child inherits the Y chromosome from his father. The presence of the Y chromosome is what distinguishes a male child from a female child, as it pairs with the X chromosome inherited from the mother to form the male's XY chromosome pattern.

Key Concepts

X Chromosome

The X chromosome is one of the two sex chromosomes in humans. While both males and females inherit an X chromosome, the role it plays can differ. In females, two X chromosomes (XX) are present, one inherited from each parent. This means that females have a so-called 'XX' chromosome pair.

The X chromosome contains many genes that are not related to sex determination but are essential for various body functions.

• It influences certain hereditary traits and conditions.
• The X chromosome is larger than the Y chromosome and carries more genes.

Understanding the X chromosome's role is crucial for grasping how sex is determined, as it is a key part of the genetic makeup that decides gender in combination with the Y chromosome.

Y Chromosome

The Y chromosome, unlike its X counterpart, is present only in males. It is a defining factor for male characteristics, primarily responsible for determining a male's genetic sex. Each male receives one Y chromosome, passed down exclusively from their father.

The Y chromosome is much smaller than the X chromosome and contains fewer genes.

• It contains crucial genetic material for the development of male-specific traits.
• The Y chromosome carries the SRY gene, which triggers the formation of testes and the subsequent male sexual development.

Without the Y chromosome, an embryo will develop into a female, which highlights its central role in gender differentiation among human beings.

Gender Determination

Gender determination in humans hinges on the combination of X and Y chromosomes. Females have two X chromosomes, while males are characterized by one X and one Y chromosome. The specific chromosomes inherited from each parent dictate whether a child will develop as male or female.

Here's how it works in simple terms:

• A mother can only pass on an X chromosome since she has two Xs.
• A father, on the other hand, can pass either an X or a Y chromosome.

If a child inherits an X chromosome from the father, the combination is XX, resulting in a female child. If the child inherits a Y chromosome from the father, the combination is XY, resulting in a male child. This natural mechanism of chromosome inheritance leads to the diverse gender identities observable in humans.