Question Video: Determining the Probability of a Successful Fertilization Producing a Female Offspring | Nagwa Question Video: Determining the Probability of a Successful Fertilization Producing a Female Offspring | Nagwa

# Question Video: Determining the Probability of a Successful Fertilization Producing a Female Offspring Biology • First Year of Secondary School

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A couple are expecting a child. What is the probability, in percent, that this child will be born female?

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### Video Transcript

A couple are expecting a child. What is the probability, in percent, that this child will be born female? (A) 50 percent, (B) 25 percent, (C) 75 percent, (D) 100 percent, (E) 33.3 percent.

In order to answer this question correctly, let’s review how biological sex is determined in humans.

Most cells in the human body are called somatic cells. And they make up every organ and tissue apart from the sex cells which are located in the gonads. While human somatic cells typically contain 46 chromosomes, sex cells only contain 23 chromosomes. The 23rd chromosome is a sex chromosome and can be either an X or a Y chromosome. It is the pair of sex chromosomes in somatic cells that will determine the biological sex of the offspring as the pair sex of chromosomes are different in biological males and females.

Each gamete contains one of the sex chromosomes. In human females, gametes are called ova, or egg cells, while the human male gametes are called sperm cells. Human female somatic cells possess two copies of the X chromosome, while human male somatic cells possess one X and one Y chromosome. Since human females possess only X chromosomes, the ovum, or egg cell, always contributes one X chromosome to the offspring’s sex chromosome pair. In contrast, since human males have an X and Y chromosome, they can contribute either an X or Y chromosome to the offspring’s sex chromosome pair.

If we put this information in a Punnett square, we can determine the probability of the sex chromosomes of the offspring. From the Punnett square, we can see that half of the sperm will produce offspring with XX chromosomes upon fertilization. The other half of the sperm will produce offspring with XY chromosomes. So, for each successful fertilization, the fetus has a 50 percent chance of being male and a 50 percent chance of being female.

With this information, we are able to answer the question. The probability that a child will be born female is 50 percent, and this is determined by the sex chromosome carried by the sperm cell.

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