Sex Determination in Humans – Class 12 | Chapter – 5 | Biology Short Notes Series PDF

Sex Determination in Humans: In humans, sex determination is the process that determines the biological sex of an offspring and, as a result, the sexual characteristics that they will develop. Humans typically develop as either male or female, primarily depending on the combination of sex chromosomes that they inherit from their parents.

The mechanisms for sex determination are genotypic sex determination systems, in which sex is governed by the genotype of the zygote and environmental sex determination systems in which sex is governed by internal and external environmental conditions. In genotypic sex determination the sex chromosomes play a decisive role in the inheritance and determination of sex.

• Chromosomal sex is determined at fertilization.
• Sexual differences begin in the 7th week.
• Sex is influenced by genetic and environmental factors.
• Females (generally XX) do not have a Y chromosome.
• Males (generally XY) have a Y chromosome.

• Sex determination mechanism is humans is XY type.
• 22 pairs are similar in male & females whereas presence of X/Y chromosomes determine human sex.
• In spermatogenesis male produce 50% of sperms with X-Chromosomes and the other 50% with Y-Chromosomes.
• Female have only X-Chromosomes.
• It is hence a matter of chance, since there is equal probability of getting fertilized with sperm carrying X or Y chromosomes.
  • If X chromosome gets fertilized – XX (Female)
  • If Y chromosome gets fertilized – XY (Male)

Sex Determination in Humans

• Humans have 23 pairs of chromosomes. Out of these 23 pairs, 22 pairs are Autosomes and only one pair is the ‘Sex Chromosome’, which actively takes part in the process of sex determination.
• Both males and females carry two sets of sex chromosome.
• Male has one X and one Y (XY) sex chromosome in which both are active
• Female has both X (XX) sex chromosome in which one is active.
• The XY sex-determination system is found in humans, mammals, in some insects, and in few plant species.
• All children will inherit an X chromosome from their mother, despite whether they are a boy or girl. Thus, the sex of the children will be determined by the type of chromosome inherited from their father.
• A child who inherits Y chromosome will be a boy and who inherits X chromosome will be a girl.

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By Team Learning Mantras