Example punnet square for sex-linked recessive trait | High school biology | Khan Academy | Summary and Q&A

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May 3, 2018
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Example punnet square for sex-linked recessive trait | High school biology | Khan Academy

TL;DR

There is a 50% chance that a daughter of a carrier woman and a hemophiliac man will have hemophilia.

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Key Insights

  • ☺️ Hemophilia is an X-linked recessive trait that affects blood clotting.
  • πŸ€΅β€β™€οΈ A carrier woman has one normal X chromosome and one with the mutated gene for hemophilia.
  • ☺️ Hemophilia occurs in males because they only have one X chromosome.
  • ❎ The Punnett square can be used to determine the probability of different outcomes for offspring.
  • πŸ§”β€β™€οΈ In this case, there is a 50% chance that a daughter of a carrier woman and a hemophiliac man will have hemophilia.
  • πŸ’€ The Punnett square can also be used to calculate the probability of other outcomes, such as having a hemophiliac son or a non-hemophiliac son.
  • ❎ Two out of the four scenarios in the Punnett square show the potential for hemophiliac offspring, resulting in a 50% chance.

Transcript

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Questions & Answers

Q: What is hemophilia and how does it affect blood clotting?

Hemophilia is an X-linked recessive trait, meaning it is caused by a mutation on the X chromosome. This mutation affects the production of a protein necessary for blood clotting, leading to prolonged bleeding and difficulty in clot formation.

Q: What does it mean for a woman to be a carrier of hemophilia?

A carrier woman has one copy of the mutated gene on one of her X chromosomes, while the other X chromosome carries the normal gene. As a carrier, she does not exhibit symptoms of hemophilia but can pass on the mutated gene to her children.

Q: Why does a hemophiliac man only have one X chromosome?

Males have one X and one Y chromosome. In the case of a hemophiliac man, his one X chromosome carries the mutated gene responsible for hemophilia.

Q: How is a Punnett square used to determine the probability of offspring inheriting hemophilia?

A Punnett square is a simple diagram that shows all the possible combinations of alleles from parents. By filling in the squares with the different alleles from the mother and father, one can determine the probability of specific outcomes, such as the chance of a daughter having hemophilia.

Summary & Key Takeaways

  • Hemophilia is an X-linked recessive trait that affects blood clotting.

  • If a carrier woman and a hemophiliac man have a daughter, there is a 50% chance she will have hemophilia.

  • The Punnett square can be used to answer various questions about the probability of different outcomes.

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