Sex Determination in Humans: Definition, Overview, Examples, Explanation

Sex Determination in Humans is a process that decides whether an individual is male or female. In humans, Sex Determination depends on X and Y chromosomes. It happens during the fertilisation process. Humans inherit one sex chromosome from each parent. The Determination of sex in humans depends on the combination of these sex chromosomes during fertilisation.

This Story also Contains

1. What Is Sex Determination in Humans?
2. Chromosomal Basis Of Sex Determination
3. Role of Autosomes and Sex Chromosomes
4. Disorders Of Sex Development (DSDs)
5. Environmental And Epigenetic Factors
6. The Video Recommended On Sex Determination In Humans:
7. MCQs on Sex Determination In Humans

Understanding Sex Determination in humans helps in the study of genetics, human reproduction, and inherited traits. It also explains how different sex chromosomes influence the development of sexual characteristics in boys and girls. In biology, knowledge of Sex Determination in Humans is important for medical science, mainly when studying human genetic disorders related to X and Y chromosomes.

What Is Sex Determination in Humans?

Sex determination in Humans refers to the biological process by which sexual characteristics in reproduction are determined in humans. It is mainly determined by the combination of the sex chromosomes, each from his or her parents. In every individual's sex inheritance, there is one sex chromosome from each parent. The combination expresses either the male chromosomal pattern XY or the female pattern XX. This mechanism ensures definite development for sexual traits and reproductive functions. It is very important for the perpetuation of species.

Chromosomal Basis Of Sex Determination

Sex determination in humans is based on the system of chromosomes XX/XY. This system defines sex based on the combination of X and Y chromosomes. That system defines:

1. Females (XX): Each cell has two X chromosomes. One X chromosome is inherited from the mother (maternal origin). The other X chromosome is inherited from the father (paternal origin).

2. Males (XY): Every cell contains one X chromosome received from the mother and one Y chromosome received from the father. The Y chromosome is crucial for the development of male characteristics.

Role of Autosomes and Sex Chromosomes

The role of Autosomes and Sex Chromosomes is a key concept in understanding sex determination in humans. Humans have two types of chromosomes—autosomes and allosomes—both essential in genetics.

Disorders Of Sex Development (DSDs)

Disorders of Sex Development (DSDs) refer to conditions where the sex determination in humans does not follow the typical chromosomal, gonadal, or anatomical sex development patterns. This may include ambiguous genitalia and a mismatch between chromosomal sex and physical appearance. Understanding disorders of sex development is important in genetics, biology, and medicine because these conditions affect the normal process of sex determination in humans.

Examples of DSDs

Androgen Insensitivity Syndrome: It is a case whereby a person in possession of a male genome, XY, is resistant to male hormones (androgens).

Klinefelter Syndrome: This is a sex development disorder in males wherein an extra X chromosome is present, XXY.

Turner Syndrome: A condition in which females are completely or partially lacking one of the sex chromosomes, XO. This mostly results in short stature, delayed puberty, infertility, heart defects, and some learning disabilities.

Environmental And Epigenetic Factors

The environmental and epigenetic factors in sex determination play a supportive role alongside gene interaction in influencing human sexual development. These factors are described below:

Influence Of Exogenous Factors On Sex Determination

In many species, environmental factors like temperature and chemicals influence sex determination. In humans, these factors affect hormonal levels and development indirectly.

Role Of Epigenetics In Sex Differentiation

Epigenetics refers to gene expression changes without DNA sequence changes. Mechanisms like DNA methylation and histone modification regulate sex differentiation. Epigenetic changes influence the expression of the SRY gene and cellular response to sex hormones.

The Video Recommended On Sex Determination In Humans:

MCQs on Sex Determination In Humans

Question: Sex determination in humans is

1. XX- XY type

2. XX- XO type

3. ZW - ZZ type

4. ZO - ZZ type

Answer: Human sex determination is of the XX-XY kind.

• There are two X chromosomes (XX) in females.

• One X chromosome and one Y chromosome (XY) are present in males.

• The father's contribution of sperm determines the sex of the child. The child will be female (XX) if the sperm has an X chromosome. It will produce male progeny (XY) if it possesses a Y chromosome.

Hence, the correct answer is option 1)XX- XY type.

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

1. Two X chromosomes

2. Only one Y chromosome

3. Only one X chromosome

4. Only X and one Y chromosome

Answer: XY-type of sex determination mechanism -

In this type, the male has an X-chromosome along with its counterpart distinctly smaller Y-chromosome and females have a pair of X-chromosomes. E.g. in mammals and humans. The XY-type sex-determination system is the most common mechanism in mammals, including humans. In this system, males are heterogametic, possessing one X and one smaller Y chromosome (XY), while females are homogametic with two X chromosomes (XX). The Y chromosome carries the SRY gene, which triggers the development of male characteristics, including testes formation. The presence of two X chromosomes in females leads to the development of female traits, such as ovaries. This system of sex determination plays a crucial role in sexual differentiation and reproductive function in mammals.

Hence, the correct answer is option 1) Two X chromosomes.

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

(1) If both the Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark A

(2) If both the Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark B

(3) If the Assertion is a true statement but the Reason is false, then mark C

(4) If both Assertion and Reason are false statements, then mark D

Assertion: The XX genotype typically leads to female sex determination, while the XY genotype typically leads to male sex determination.

Reason: Sex determination in mammals is determined by the presence or absence of the Y chromosome. In the absence of the Y chromosome, the default pathway leads to the development of female characteristics. In the presence of the Y chromosome, the SRY gene located on the Y chromosome leads to the development of male characteristics.

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

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

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

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

Answer: Sex determination in mammals is a complex process that involves the interplay of many genes and hormonal signals. However, the presence or absence of the Y chromosome is a major determinant of whether an individual develops male or female characteristics.

In individuals with the XX genotype, the absence of the Y chromosome leads to the default pathway of female sex determination. The ovaries develop and produce estrogen, which leads to the development of female secondary sexual characteristics such as breasts, a menstrual cycle, and a female body shape.

In individuals with the XY genotype, the presence of the Y chromosome and the SRY gene located on it leads to the development of male sex characteristics. The testes develop and produce testosterone, which leads to the development of male secondary sexual characteristics such as facial hair, a deep voice, and a male body shape.

Therefore, the assertion that the XX genotype typically leads to female sex determination, while the XY genotype typically leads to male sex determination is true, and the reason for this is the presence or absence of the Y chromosome and the genes located on it.

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

Also Read:

• MCQs on Sex Determination in Humans

• 23 Chromosomes And Their Functions

• Principles Of Inheritance And Variation