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Arjun Nagpal
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Asked: 2020-10-20T12:28:16+00:00 In:

How is the sex of the child determined in human beings?

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NCERT Solution for Class 10 Science Chapter 9
Heredity and Evolution
NCERT Books for Session 2022-2023
CBSE Board and UP Board
Intext Questions
Page No-147
Questions No-4

2020-2021cbsechapter 9class10heredity and evolutionncertscience
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    6 Answers

    1. The sex of a child in human beings is determined by the combination of sex chromosomes inherited from the parents. Humans have 23 pairs of chromosomes, and one of these pairs is the sex chromosomes, designated as X and Y. The combination of sex chromosomes an individual receives determines their biological sex. The two possibilities are:

      1. Male (XY):

      » Males have one X chromosome and one Y chromosome (XY).
      » The Y chromosome carries the genes that determine male characteristics.

      2. Female (XX):

      » Females have two X chromosomes (XX).
      » The X chromosomes carry the genes that determine female characteristics.

      The sex chromosomes are inherited from both parents during fertilization. The mother always contributes an X chromosome, and the father can contribute either an X or a Y chromosome. The combination of the sex chromosomes in the fertilized egg determines the genetic sex of the individual.

      The process can be summarized as follows:

      » If the fertilized egg receives an X chromosome from the father (XY), the individual will develop into a male.
      » If the fertilized egg receives an X chromosome from the father (XX), the individual will develop into a female.
      The determination of the genetic sex occurs at the moment of conception when the sperm fertilizes the egg. This process is random, and the probability of conceiving a male or female child is approximately 50-50.

      It’s important to note that while the presence of the Y chromosome is associated with male development, there are cases of individuals with atypical chromosomal patterns, such as XXY (Klinefelter syndrome) or XO (Turner syndrome), which can result in variations in sexual development. However, the standard XX and XY chromosomal patterns are the basis for typical male and female development.

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    2. Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23rd pair is composed of different types of chromosomes which are named as X and Y chromosomes. The 23rd pair contains one X and one Y chromosome in a male. On the other hand, the 23rd pair in a female contains X chromosomes. This means that all the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome as the 23rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote would develop into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child.

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    3. The sex-determining mechanism in humans is the XY type. Humans contain 23 pairs of chromosomes. 22 pairs of chromosomes are the same in both males and females, which are called autosomes. The 23rd pair is different in both sexes and is known as sex chromosome.

      Females have a pair of X chromosomes and males have X and Y chromosomes as sex chromosome. Sex of child in humans is determined by the type of male haploid gamete that fuses with the female egg. During spermatogenesis, males produce two types of gametes, half of the sperms have an X chromosome and the other half have a Y chromosome. The female egg always has an X chromosome.

      So if the male gamete with the X chromosome fuses with the female egg, the child will be female and if the male gamete with the Y chromosome fuses with the female egg, the child will be male.

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    4. In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY.
      The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
      Type of male gametes: 22+X OR 22+ Y.
      However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
      Type of female gamete: 22+X
      Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.

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    6. Half of the male gametes (sperms) carry X chromosome and other half carry Y chromosomes. All the female gametes carry only X chromosomes. When a sperm fertilizes an egg, the following situations become possible.

      (i) When a sperm carrying X chromosome fertilises an egg that contains only X chromosome), the resulting zygote develops into a female (XX condition).
      (ii) When a sperm carrying Y chromosome fertilises an egg (that contains only X chromosome), the resulting zygote develops into a male (XY condition).

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    7. In human beings, the females have two X chromosomes and the males have one X and
      one Y chromosome. Therefore, the females are XX and the males are XY.
      The gametes, as we know, receive half of the chromosomes. The male gametes have 22
      autosomes and either X or Y sex chromosome.
      Type of male gametes: 22+X OR 22+ Y.
      However, since the females have XX sex chromosomes, their gametes can only have X
      sex chromosome.
      Type of female gamete: 22+X
      Thus, the mother provides only X chromosomes. The sex of the baby is determined by the
      type of male gamete (X or Y) that fuses with the X chromosome of the female.

      For more answers visit to website:
      https://www.tiwariacademy.com/ncert-solutions/class-10/science/chapter-9/

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