Sex Determination – Boy or Girl: Definition, Meaning, Topics, examples

In Sexual Reproduction, two different kinds of sexes are involved. It will be surprising to find out which sex the baby inherits, which results in the sex of the child. There are different types of procedures followed to determine the sex of the baby.

In many animal species, the environment and the temperature also play a major role. In human beings, on the other hand, the sex of the baby is completely genetic. The genes inherited from their parents determine the sex of the child. Sex determination is a key topic within the chapter Principles of Inheritance and Variation in Biology.

This Story also Contains

1. What is Sex Determination?
2. What is Fertilisation?
3. What are Chromosomes?
4. Differences between Autosomes and Sex Chromosomes
5. Recommended Video on Sex Determination
6. MCQs on Sex Determination- Boy or Girl

What is Sex Determination?

Sex determination is the process by which an organism develops into either male or female. It is determined in humans and most other organisms by specific genetic factors, particularly chromosomes. Chromosomes are very small, thread-like structures in our cell nucleus that carry genetic information. Humans have 23 pairs of chromosomes, and one pair, known as the sex chromosomes, that determines if a baby will be a boy or a girl.

At conception, the baby will receive one sex chromosome from each parent. This presents two possibilities: If the combination is XX, the baby will then be female; if the combination is XY, the baby will then be male. That occurs at fertilisation, where the sperm from the father meets the egg from the mother.

This process is important because it affects how organisms reproduce and relate to their environment. Understanding sex determination thus opens the door to the larger study of how genes function, how a few genetic diseases are passed from parent to offspring, and how animals and plants grow. Amniocentesis is the process by which the sex of the baby and whether it possesses any chromosomal abnormalities.

Not all animal species determine sex based on chromosomes. Some species, including certain reptiles and fish, decide whether or not they develop as male or female based on environmental factors such as temperature.

What is Fertilisation?

The process by which a male sperm and a female egg cell combine to form a zygote is known as fertilisation. The process of implantation initiates the development of a new organism. In the process, the nuclei of these two gametes are combined, and one-half of the genetic material from each will be for the resulting zygote. The fertilisation usually occurs in the Fallopian tubes of the female and leads to the embryo development, whereafter it is implanted in the uterus for further growth.

What are Chromosomes?

Chromosomes are the tiny, thread-like structures found in the cell nucleus of animal and plant cells. Such structures consist of DNA and proteins, which carry the genetic information responsible for transferring certain traits from parents to their offspring.

Humans have 23 pairs of chromosomes in each cell, adding up to 46. Of these, 22 pairs are identical in both males and females, known as autosomes. The 23rd pair, known as sex chromosomes, differs between males and females and determines whether a person is male or female.

Chromosomes play a very important role in ensuring the proper transmission of genetic information during cell division. Each chromosome is a tightly coiled package of DNA, which contains many genes, basic units of heredity. During cell division, the chromosomes correctly distribute DNA most of the time.

Number of Chromosomes in Humans

Humans have 46 chromosomes in every cell that are divided into 23 pairs. One chromosome of the 23rd pair comes from the mother, and the other from the father. Combined, this not only gives genetic diversity but also the capability of passing on traits from both parents. A person's sex is determined by the 23rd pair of chromosomes; females by two X chromosomes, and males by one X and one Y chromosome.

Sex Chromosomes

Sex chromosomes are one of the 23 pairs of chromosomes in a human being and are, therefore, ultimately responsible for determining a person's sex. There exist two types of sex chromosomes, X and Y. Females usually have two X sex chromosomes (XX), and males have one X and one Y chromosome (XY). This means that if the Y chromosome is present, species with that sex chromosome develop as males, and if it is absent, they develop as females.

Differences between Autosomes and Sex Chromosomes

Autosomes are those chromosomes that do not determine the sex of a baby, and they are alike in both sexes; there are 22 pairs in humans. On the other hand, sex chromosomes determine the sex of an individual and differ between males and females. The differences between autosomes and allosomes are tabulated below-

Recommended Video on Sex Determination

MCQs on Sex Determination- Boy or Girl

Q1. What is the most common method of sex determination in mammals?

Option 1: The presence or absence of the Y chromosome

Option 2: The presence or absence of the X chromosome

Option 3: Combination of sex chromosomes

Option 4: Environmental factors

Correct answer: 3) Combination of sex chromosomes

Explanation:

The most prevalent method of sex determination among mammals is the XY system. Which is the combination of sex chromosomes.

This mechanism operates through the presence of specific chromosomes:

• females typically possess a homologous pair of X chromosomes (XX)

• while males are characterized by a heterologous pair consisting of one X and one Y chromosome (XY). The critical factor initiating male development is the SRY gene, which is located on the Y chromosome. Known as the Sex-determining Region Y, this gene is instrumental in inducing the differentiation of male sex characteristics. In the absence of the SRY gene.

• As is the case in females, the organism follows a default pathway leading to the development of female traits.

Hence, the correct answer is option 3) Combination of sex chromosomes.

Q2. In the following questions, a statement of assertion (A) is followed by a statement of reason (R)

Assertion: The sex of an individual is determined by their sex chromosomes.

Reason: Males have one X and one Y chromosome, while females have two X chromosomes.

Option 1: Both Assertion (A) and Reason (R) are the true and Reason (R) is a correct explanation of Assertion (A).

Option 2: Both Assertion (A) and Reason (R) are the true but Reason (R) is not a correct explanation of Assertion (A).

Option 3: Assertion (A) is true and Reason (R) is false.

Option 4: Assertion (A) is false and Reason (R) is true.

Correct answer: 1) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A).

Explanation:

The sex of an individual is determined by the sex chromosomes they inherit from their parents. In humans, females have two copies of the X chromosome (XX), while males have one X chromosome and one Y chromosome (XY).

During fertilization, a sperm carrying either an X or Y chromosome can fuse with an egg carrying an X chromosome, resulting in the formation of a female (XX) or male (XY) embryo, respectively.

Therefore, it is correct to say that the sex of an individual is determined by their sex chromosomes. Additionally, it is correct to say that males have one X and one Y chromosome, while females have two X chromosomes.

So, in summary, the sex of an individual is determined by their sex chromosomes, males have one X and one Y chromosome, while females have two X chromosomes.

Hence, the correct answer is option is 1) Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A).

Q3. Which one of the following conditions of the zygotic cell would lead to the birth of a normal human female child?

Option 1: Only one X chromosome

Option 2: One X and one Y chromosome

Option 3: Two X chromosomes

Option 4: Only one Y chromosome

Correct answer: 3) Two X chromosomes

Explanation:

At birth, females have two X chromosomes. (XX). One X and one Y chromosome are present in males. Any condition wherein such a chromosome number is altered would lead to an abnormality.

Hence, the correct answer is option 3) Two X chromosomes.

Also Read:

• MCQ Practice on Sex Determination in Humans

• Principles of Inheritance and Variation

• Molecular Basis of Inheritance